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• What is the rationale to non allow overloading of C++ conversions operator with non-member functio

  - by Vicente Botet Escriba

  C++0x has added explicit conversion operators, but they must always be defined as members of the Source class. The same applies to the assignment operator, it must be defined on the Target class. When the Source and Target classes of the needed conversion are independent of each other, neither the Source can define a conversion operator, neither the Target can define a constructor from a Source. Usually we get it by defining a specific function such as Target ConvertToTarget(Source& v); If C++0x allowed to overload conversion operator by non member functions we could for example define the conversion implicitly or explicitly between unrelated types. template < typename To, typename From operator To(const From& val); For example we could specialize the conversion from chrono::time_point to posix_time::ptime as follows template < class Clock, class Duration operator boost::posix_time::ptime( const boost::chrono::time_point& from) { using namespace boost; typedef chrono::time_point time_point_t; typedef chrono::nanoseconds duration_t; typedef duration_t::rep rep_t; rep_t d = chrono::duration_cast( from.time_since_epoch()).count(); rep_t sec = d/1000000000; rep_t nsec = d%1000000000; return posix_time::from_time_t(0)+ posix_time::seconds(static_cast(sec))+ posix_time::nanoseconds(nsec); } And use the conversion as any other conversion. So the question is: What is the rationale to non allow overloading of C++ conversions operator with non-member functions?

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• Join + IEqualityComparer<T> and HashCode

  - by Jesus Rodriguez

  Im writing my own LINQ reference but Im getting troubles with some of the more complicated operators implementations. There is a Join implementation that takes a IEqualityComparer Im getting just crazy. Im trying to understand it first before I write (obviously) Image this two lists: List<string> initials = new List<string> {"A", "B", "C", "D", "E"}; List<string> words = new List<string> {"Ant", "Crawl", "Pig", "Boat", "Elephant", "Arc"}; Nothing weird here. I want to join both lists by the Initial, something like: Initial=A Word=Ant Initial=A Word=Arc Initial=B Word=Boat ... I need a comparator, I wrote this: public class InitialComparator : IEqualityComparer<string> { public bool Equals(string x, string y) { return x.StartsWith(y); } public int GetHashCode(string obj) { return obj[0].GetHashCode(); } } The Join itself: var blah = initials.Join(words, initial => initial, word => word, (initial, word) => new {Initial = initial, Word = word}, new InitialComparator()); It's the first time Im using HashCodes, after a good session of debugging I see that every word go to the comparator and look at its HashCode, if another word has the same HashCode it calls equals. Since I want to compare just the initial I though that I just need the first letter Hash (Am I wrong?) The thing is that this is not working correctly. Its says that "Ant" and "Arc" are equals, Ok, its comparing every word in the same list or not, But it adds only the last word it finds, in this case Arc, ignoring Ant and Ant is equals to "A" too... If I put "Ant" and "Ant" it add both. In short, What is the way of doing something like that? I know that Im doing something wrong. Thank you.

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• Search book by title, and author

  - by Swoosh

  I got a table with columns: author firstname, author lastname, and booktitle Multiple users are inserting in the database, through an import, and I'd like to avoid duplicates. So I'm trying to do something like this: I have a record in the db: First Name: "Isaac" Last Name: "Assimov" Title: "I, Robot" If the user tries to add it again, it would be basically a non-split-text (would not be split up into author firstname, author lastname, and booktitle) So it would basically look like this: "Isaac Asimov - I Robot" or "Asimov, Isaac - I Robot" or "I Robot by Isaac Asimov" You see where I am getting at? (I cannot force the user to split up all the books into into author firstname, author lastname, and booktitle, and I don't even like the idea to force the user, because it's not too user-friendly) What is the best way (in SQL) to compare all this possible bookdata scenarios to what I have in the database, not to add the same book twice. I was thinking about a possibility of suggesting the user: "is THIS the book you are trying to add?" (imagine a list instead of the THIS word, just like on stackoverflow - ask question - Related Questions. I was thinking about soundex and maybe even the like operators, but so far i didn't get the results i was hoping.

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• Auto-(un)boxing fail for compound assignment

  - by polygenelubricants

  Thanks to the implicit casting in compound assignments and increment/decrement operators, the following compiles: byte b = 0; ++b; b++; --b; b--; b += b -= b *= b /= b %= b; b <<= b >>= b >>>= b; b |= b &= b ^= b; And thanks to auto-boxing and auto-unboxing, the following also compiles: Integer ii = 0; ++ii; ii++; --ii; ii--; ii += ii -= ii *= ii /= ii %= ii; ii <<= ii >>= ii >>>= ii; ii |= ii &= ii ^= ii; And yet, the last line in the following snippet gives compile-time error: Byte bb = 0; ++bb; bb++; --bb; bb--; // ... okay so far! bb += bb; // DOESN'T COMPILE!!! // "The operator += is undefined for the argument type(s) Byte, byte" Can anyone help me figure out what's going on here? The byte b version compiles just fine, so shouldn't Byte bb just follow suit and do the appropriate boxing and unboxing as necessary to accommodate?

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• Update mapping table in Linq

  - by Gary McGill

  I have a table Customers with a CustomerId field, and a table of Publications with a PublicationId field. Finally, I have a mapping table CustomersPublications that records which publications a customer can access - it has two fields: CustomerId field PublicationId. For a given customer, I want to update the CustomersPublications table based on a list of publication ids. I want to remove records in CustomersPublications where the PublicationId is not in the list, and add new records where the PublicationId is in the list but not already in the table. This would be easy in SQL, but I can't figure out how to do it in Linq. For the delete part, I tried: var recordsToDelete = dataContext.CustomersPublications.Where ( cp => (cp.CustomerId == customerId) && ! publicationIds.Contains(cp.PublicationId) ); dataContext.CustomersPublications.DeleteAllOnSubmit(recordsToDelete); ... but that didn't work. I got an error: System.NotSupportedException: Method 'Boolean Contains(Int32)' has no supported translation to SQL So, I tried using Any(), as follows: var recordsToDelete = dataContext.CustomersPublications.Where ( cp => (cp.CustomerId == customerId) && ! publicationIds.Any(p => p == cp.PublicationId) ); ... and this just gives me another error: System.NotSupportedException: Local sequence cannot be used in LINQ to SQL implementation of query operators except the Contains() operator Any pointers? [I have to say, I find Linq baffling (and frustrating) for all but the simplest queries. Better error messages would help!]

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• Pronunciation of programming structures (particularly in c#)

  - by Andrzej Nosal

  As a non-English speaking person I often have problems pronouncing certain programming structures and abbreviations. I've been watching some video tutorials and listening to podcasts as well, though I couldn't catch them all. My question is what is the common or correct pronunciation of the following code snippets? Generics, like IEnumerable<int> or in a method void Swap<T>(T lhs, T rhs) Collections indexing and indexer access e.g. garage[i], rectangular arrays myArray[2,1] or jagged[1][2][3] Lambda operator =>, e.g. in a where extension method .Where(animal => animal.Color == Color.Brown) or in an anonymous method () => { return false;} Inheritance class Derived : Base (extends?) class SomeClass : IDisposable (implements?) Arithemtic operators += -= *= /= %= ! Are += and -= pronounced the same for events? Collections initializers new int[] { 4, 5, 8, 9, 12, 13, 16, 17 }; Casting MyEnum foo = (MyEnum)(int)yourFloat; (as?) Nullables DateTime? dt = new DateTime?(); I tagged the question with C# as some of them are specific to C# only.

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• rails: has_many :through validation?

  - by ramonrails

  Rails 2.1.0 (Cannot upgrade for now due to several constraints) I am trying to achieve this. Any hints? A project has many users through join model A user has many projects through join model Admin class inherits User class. It also has some Admin specific stuff. Admin like inheritance for Supervisor and Operator Project has one Admin, One supervisor and many operators. Now I want to 1. submit data for project, admin, supervisor and operator in a single project form 2. validate all and show errors on the project form. Project has_many :projects_users ; has_many :users, :through => :projects_users User has_many :projects_users ; has_many :projects, :through => :projects_users ProjectsUser = :id integer, :user_id :integer, :project_id :integer, :user_type :string ProjectUser belongs_to :project, belongs_to :user Admin < User # User has 'type:string' column for STI Supervisor < User Operator < User Is the approach correct? Any and all suggestions are welcome.

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• What's your preferred pointer declaration style, and why?

  - by Owen

  I know this is about as bad as it gets for "religious" issues, as Jeff calls them. But I want to know why the people who disagree with me on this do so, and hear their justification for their horrific style. I googled for a while and couldn't find a style guide talking about this. So here's how I feel pointers (and references) should be declared: int* pointer = NULL; int& ref = *pointer; int*& pointer_ref = pointer; The asterisk or ampersand goes with the type, because it modifies the type of the variable being declared. EDIT: I hate to keep repeating the word, but when I say it modifies the type I'm speaking semantically. "int* something;" would translate into English as something like "I declare something, which is a pointer to an integer." The "pointer" goes along with the "integer" much more so than it does with the "something." In contrast, the other uses of the ampersand and asterisk, as address-of and dereferencing operators, act on a variable. Here are the other two styles (maybe there are more but I really hope not): int *ugly_but_common; int * uglier_but_fortunately_less_common; Why? Really, why? I can never think of a case where the second is appropriate, and the first only suitable perhaps with something like: int *hag, *beast; But come now... multiple variable declarations on one line is kind of ugly form in itself already.

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• heterogeneous comparisons in python3

  - by Matt Anderson

  I'm 99+% still using python 2.x, but I'm trying to think ahead to the day when I switch. So, I know that using comparison operators (less/greater than, or equal to) on heterogeneous types that don't have a natural ordering is no longer supported in python3.x -- instead of some consistent (but arbitrary) result we raise TypeError instead. I see the logic in that, and even mostly think its a good thing. Consistency and refusing to guess is a virtue. But what if you essentially want the python2.x behavior? What's the best way to go about getting it? For fun (more or less) I was recently implementing a Skip List, a data structure that keeps its elements sorted. I wanted to use heterogeneous types as keys in the data structure, and I've got to compare keys to one another as I walk the data structure. The python2.x way of comparing makes this really convenient -- you get an understandable ordering amongst elements that have a natural ordering, and some ordering amongst those that don't. Consistently using a sort/comparison key like (type(obj).__name__, obj) has the disadvantage of not interleaving the objects that do have a natural ordering; you get all your floats clustered together before your ints, and your str-derived class separates from your strs. I came up with the following: import operator def hetero_sort_key(obj): cls = type(obj) return (cls.__name__+'_'+cls.__module__, obj) def make_hetero_comparitor(fn): def comparator(a, b): try: return fn(a, b) except TypeError: return fn(hetero_sort_key(a), hetero_sort_key(b)) return comparator hetero_lt = make_hetero_comparitor(operator.lt) hetero_gt = make_hetero_comparitor(operator.gt) hetero_le = make_hetero_comparitor(operator.le) hetero_ge = make_hetero_comparitor(operator.gt) Is there a better way? I suspect one could construct a corner case that this would screw up -- a situation where you can compare type A to B and type A to C, but where B and C raise TypeError when compared, and you can end up with something illogical like a > b, a < c, and yet b > c (because of how their class names sorted). I don't know how likely it is that you'd run into this in practice.

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• Recommended textbook for machine-level programming?

  - by Norman Ramsey

  I'm looking at textbooks for an undergraduate course in machine-level programming. If the perfect book existed, this is what it would look like: Uses examples written in C or assembly language, or both. Covers machine-level operations such as two's-complement integer arithmetic, bitwise operations, and floating-point arithmetic. Explains how caches work and how they affect performance. Explains machine instructions or assembly instructions. Bonus if the example assembly language includes x86; triple bonus if it includes x86-64 (aka AMD64). Explains how C values and data structures are represented using hardware registers and memory. Explains how C control structures are translated into assembly language using conditional and unconditional branch instructions. Explains something about procedure calling conventions and how procedure calls are implemented at the machine level. Books I might be interested in would probably have the words "machine organization" or "computer architecture" in the title. Here are some books I'm considering but am not quite happy with: Computer Systems: A Programmer's Perspective by Randy Bryant and Dave O'Hallaron. This is quite a nice book, but it's a book for a broad, shallow course in systems programming, and it contains a great deal of material my students don't need. Also, it is just out in a second edition, which will make it expensive. Computer Organization and Design: The Hardware/Software Interface by Dave Patterson and John Hennessy. This is also a very nice book, but it contains way more information about how the hardware works than my students need. Also, the exercises look boring. Finally, it has a show-stopping bug: it is based very heavily on MIPS hardware and the use of a MIPS simulator. My students need to learn how to use DDD, and I can't see getting this to work on a simulator. Not to mention that I can't see them cross-compiling their code for the simulator, and so on and so forth. Another flaw is that the book mentions the x86 architecture only to sneer at it. I am entirely sympathetic to this point of view, but news flash! You guys lost! Write Great Code Vol I: Understanding the Machine by Randall Hyde. I haven't evaluated this book as thoroughly as the other two. It has a lot of what I need, but the translation from high-level language to assembler is deferred to Volume Two, which has mixed reviews. My students will be annoyed if I make them buy a two-volume series, even if the price of those two volumes is smaller than the price of other books. I would really welcome other suggestions of books that would help students in a class where they are to learn how C-language data structures and code are translated to machine-level data structures and code and where they learn how to think about performance, with an emphasis on the cache.

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• LINQ to SQL - How to efficiently do either an AND or an OR search for multiple criteria

  - by Dan Diplo

  I have an ASP.NET MVC site (which uses Linq To Sql for the ORM) and a situation where a client wants a search facility against a bespoke database whereby they can choose to either do an 'AND' search (all criteria match) or an 'OR' search (any criteria match). The query is quite complex and long and I want to know if there is a simple way I can make it do both without having to have create and maintain two different versions of the query. For instance, the current 'AND' search looks something like this (but this is a much simplified version): private IQueryable<SampleListDto> GetSampleSearchQuery(SamplesCriteria criteria) { var results = from r in Table where (r.Id == criteria.SampleId) && (r.Status.SampleStatusId == criteria.SampleStatusId) && (r.Job.JobNumber.StartsWith(criteria.JobNumber)) && (r.Description.Contains(criteria.Description)) select r; } I could copy this and replace the && with || operators to get the 'OR' version, but feel there must be a better way of achieving this. Does anybody have any suggestions how this can be achieved in an efficient and flexible way that is easy to maintain? Thanks.

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• How to avoid repetition when working with primitive types?

  - by I82Much

  I have the need to perform algorithms on various primitive types; the algorithm is essentially the same with the exception of which type the variables are. So for instance, /** * Determine if <code>value</code> is the bitwise OR of elements of <code>validValues</code> array. * For instance, our valid choices are 0001, 0010, and 1000. * We are given a value of 1001. This is valid because it can be made from * ORing together 0001 and 1000. * On the other hand, if we are given a value of 1111, this is invalid because * you cannot turn on the second bit from left by ORing together those 3 * valid values. */ public static boolean isValid(long value, long[] validValues) { for (long validOption : validValues) { value &= ~validOption; } return value != 0; } public static boolean isValid(int value, int[] validValues) { for (int validOption : validValues) { value &= ~validOption; } return value != 0; } How can I avoid this repetition? I know there's no way to genericize primitive arrays, so my hands seem tied. I have instances of primitive arrays and not boxed arrays of say Number objects, so I do not want to go that route either. I know there are a lot of questions about primitives with respect to arrays, autoboxing, etc., but I haven't seen it formulated in quite this way, and I haven't seen a decisive answer on how to interact with these arrays. I suppose I could do something like: public static<E extends Number> boolean isValid(E value, List<E> numbers) { long theValue = value.longValue(); for (Number validOption : numbers) { theValue &= ~validOption.longValue(); } return theValue != 0; } and then public static boolean isValid(long value, long[] validValues) { return isValid(value, Arrays.asList(ArrayUtils.toObject(validValues))); } public static boolean isValid(int value, int[] validValues) { return isValid(value, Arrays.asList(ArrayUtils.toObject(validValues))); } Is that really much better though? Any thoughts in this matter would be appreciated.

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• error in finding out the lexems and no of lines of a text file in C

  - by mekasperasky

  #include<stdio.h> #include<ctype.h> #include<string.h> int main() { int i=0,j,k,lines_count[2]={1,1},operand_count[2]={0},operator_count[2]={0},uoperator_count[2]={0},control_count[2]={0,0},cl[13]={0},variable_dec[2]={0,0},l,p[2]={0},ct,variable_used[2]={0,0},constant_count[2],s[2]={0},t[2]={0}; char a,b[100],c[100]; char d[100]={0}; j=30; FILE *fp1[2],*fp2; fp1[0]=fopen("program1.txt","r"); fp1[1]=fopen("program2.txt","r"); //the source file is opened in read only mode which will passed through the lexer fp2=fopen("ccv1ouput.txt","wb"); //now lets remove all the white spaces and store the rest of the words in a file if(fp1[0]==NULL) { perror("failed to open program1.txt"); //return EXIT_FAILURE; } if(fp1[1]==NULL) { perror("failed to open program2.txt"); //return EXIT_FAILURE; } i=0; k=0; ct=0; while(ct!=2) { while(!feof(fp1[ct])) { a=fgetc(fp1[ct]); if(a!=' '&&a!='\n') { if (!isalpha(a) && !isdigit(a)) { switch(a) { case '+':{ i=0; cl[0]=1; operator_count[ct]=operator_count[ct]+1;break;} case '-':{ cl[1]=1; operator_count[ct]=operator_count[ct]+1;i=0;break;} case '*':{ cl[2]=1; operator_count[ct]=operator_count[ct]+1;i=0;break;} case '/':{ cl[3]=1; operator_count[ct]=operator_count[ct]+1;i=0;break;} case '=':{a=fgetc(fp1[ct]); if (a=='='){cl[4]=1; operator_count[ct]=operator_count[ct]+1; operand_count[ct]=operand_count[ct]+1;} else { cl[5]=1; operator_count[ct]=operator_count[ct]+1; operand_count[ct]=operand_count[ct]+1; ungetc(1,fp1[ct]); } break;} case '%':{ cl[6]=1; operator_count[ct]=operator_count[ct]+1;i=0;break;} case '<':{ a=fgetc(fp1[ct]); if (a=='=') {cl[7]=1; operator_count[ct]=operator_count[ct]+1;} else { cl[8]=1; operator_count[ct]=operator_count[ct]+1; ungetc(1,fp1[ct]); } break; } case '>':{ ; a=fgetc(fp1[ct]); if (a=='='){cl[9]=1; operator_count[ct]=operator_count[ct]+1;} else { cl[10]=1; operator_count[ct]=operator_count[ct]+1; ungetc(1,fp1[ct]); } break;} case '&':{ cl[11]=1; a=fgetc(fp1[ct]); operator_count[ct]=operator_count[ct]+1; operand_count[ct]=operand_count[ct]+1; variable_used[ct]=variable_used[ct]-1; break; } case '|':{ cl[12]=1; a=fgetc(fp1[ct]); operator_count[ct]=operator_count[ct]+1; operand_count[ct]=operand_count[ct]+1; variable_used[ct]=variable_used[ct]-1; break; } case '#':{ while(a!='\n') { a=fgetc(fp1[ct]); } } } } else { d[i]=a; i=i+1; k=k+1; } } else { //printf("%s \n",d); if((strcmp(d,"if")==0)){ memset ( d, 0, 100 ); i=0; control_count[ct]=control_count[ct]+1; } else if(strcmp(d,"then")==0){ i=0;memset ( d, 0, 100 );control_count[ct]=control_count[ct]+1;} else if(strcmp(d,"else")==0){ i=0;memset ( d, 0, 100 );control_count[ct]=control_count[ct]+1;} else if(strcmp(d,"while")==0){ i=0;memset ( d, 0, 100 );control_count[ct]=control_count[ct]+1;} else if(strcmp(d,"int")==0){ while(a != '\n') { a=fgetc(fp1[ct]); if (isalpha(a) ) variable_dec[ct]=variable_dec[ct]+1; } memset ( d, 0, 100 ); lines_count[ct]=lines_count[ct]+1; } else if(strcmp(d,"char")==0){while(a != '\n') { a=fgetc(fp1[ct]); if (isalpha(a) ) variable_dec[ct]=variable_dec[ct]+1; } memset ( d, 0, 100 ); lines_count[ct]=lines_count[ct]+1; } else if(strcmp(d,"float")==0){while(a != '\n') { a=fgetc(fp1[ct]); if (isalpha(a) ) variable_dec[ct]=variable_dec[ct]+1; } memset ( d, 0, 100 ); lines_count[ct]=lines_count[ct]+1; } else if(strcmp(d,"printf")==0){while(a!='\n') a=fgetc(fp1[ct]); memset(d,0,100); } else if(strcmp(d,"scanf")==0){while(a!='\n') a=fgetc(fp1[ct]); memset(d,0,100);} else if (isdigit(d[i-1])) { memset ( d, 0, 100 ); i=0; constant_count[ct]=constant_count[ct]+1; operand_count[ct]=operand_count[ct]+1; } else if (isalpha(d[i-1]) && strcmp(d,"int")!=0 && strcmp(d,"char")!=0 && strcmp(d,"float")!=0 && (strcmp(d,"if")!=0) && strcmp(d,"then")!=0 && strcmp(d,"else")!=0 && strcmp(d,"while")!=0 && strcmp(d,"printf")!=0 && strcmp(d,"scanf")!=0) { memset ( d, 0, 100 ); i=0; operand_count[ct]=operand_count[ct]+1; } else if(a=='\n') { lines_count[ct]=lines_count[ct]+1; memset ( d, 0, 100 ); } } } fclose(fp1[ct]); operand_count[ct]=operand_count[ct]-5; variable_used[0]=operand_count[0]-constant_count[0]; variable_used[1]=operand_count[1]-constant_count[1]; for(j=0;j<12;j++) uoperator_count[ct]=uoperator_count[ct]+cl[j]; fprintf(fp2,"\n statistics of program %d",ct+1); fprintf(fp2,"\n the no of lines ---> %d",lines_count[ct]); fprintf(fp2,"\n the no of operands --->%d",operand_count[ct]); fprintf(fp2,"\n the no of operator --->%d",operator_count[ct]); fprintf(fp2,"\n the no of control statments --->%d",control_count[ct]); fprintf(fp2,"\n the no of unique operators --->%d",uoperator_count[ct]); fprintf(fp2,"\n the no of variables declared--->%d",variable_dec[ct]); fprintf(fp2,"\n the no of variables used--->%d",variable_used[ct]); fprintf(fp2,"\n ---------------------------------"); fprintf(fp2,"\n \t \t \t"); ct=ct+1; } t[0]=lines_count[0]+control_count[0]+uoperator_count[0]; t[1]=lines_count[1]+control_count[1]+uoperator_count[1]; s[0]=operator_count[0]+operand_count[0]+variable_dec[0]+variable_used[0]; s[1]=operator_count[1]+operand_count[1]+variable_dec[1]+variable_used[1]; fprintf(fp2,"\n the time complexity of program 1 is %d",t[0]); fprintf(fp2,"\n the time complexity of program 2 is %d",t[1]); fprintf(fp2,"\n the space complexity of program 1 is %d",s[0]); fprintf(fp2,"\n the space complexity of program 2 is %d",s[1]); if((t[0]>t[1]) && (s[0] >s[1])) fprintf(fp2,"\n the efficiency of program 2 is greater than program 1"); else if(t[0]<t[1] && s[0] < s[1]) fprintf(fp2,"\n the efficiency of program 1 is greater than program 2 " ); else if (t[0]+s[0] > t[1]+s[1]) fprintf(fp2,"\n the efficiency of program 1 is greater than program 2"); else if (t[0]+s[0] < t[1]+s[1]) fprintf(fp2,"\n the efficiency of program 2 is greater than program 1"); else if (t[0]+s[0] == t[1]+s[1]) fprintf(fp2,"\n the efficiency of program 1 is equal to that of program 2"); fclose(fp2); return 0; } this code basically compares two c codes and finds out the no. of variables declared , used , no. of control statements , no. of lines and no. of unique operators , and operands , so as to find out the time complexity and space complexity of of the two programs given in the text file program1.txt and program2.txt ... Lets say program1.txt is this #include<stdio.h> #include<math.h> int main () { FILE *fp; fp=fopen("output.txt","w"); long double t,y=0,x=0,e=5,f=1,w=1; for (t=0;t<10;t=t+0.01) { //if (isnan(y) || isinf(y)) //break; fprintf(fp,"%ld\t%ld\n",y,x); y = y + ((e*(1 - (x*x))*y) - x + f*cos(w*0.1))*0.1; x = x + y*0.1; } fclose(fp); return (0); } i havent indented it as its just a text file . But my output is totally faulty . Its not able to find the any of the ouput that i need . Where is the bug in this ? I am not able to figure out as the algorithm looks fine .

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• user defined Copy ctor, and copy-ctors further down the chain - compiler bug ? programmers brainbug

  - by J.Colmsee

  Hi. i have a little problem, and I am not sure if it's a compiler bug, or stupidity on my side. I have this struct : struct BulletFXData { int time_next_fx_counter; int next_fx_steps; Particle particles[2];//this is the interesting one ParticleManager::ParticleId particle_id[2]; }; The member "Particle particles[2]" has a self-made kind of smart-ptr in it (resource-counted texture-class). this smart-pointer has a default constructor, that initializes to the ptr to 0 (but that is not important) I also have another struct, containing the BulletFXData struct : struct BulletFX { BulletFXData data; BulletFXRenderFunPtr render_fun_ptr; BulletFXUpdateFunPtr update_fun_ptr; BulletFXExplosionFunPtr explode_fun_ptr; BulletFXLifetimeOverFunPtr lifetime_over_fun_ptr; BulletFX( BulletFXData data, BulletFXRenderFunPtr render_fun_ptr, BulletFXUpdateFunPtr update_fun_ptr, BulletFXExplosionFunPtr explode_fun_ptr, BulletFXLifetimeOverFunPtr lifetime_over_fun_ptr) :data(data), render_fun_ptr(render_fun_ptr), update_fun_ptr(update_fun_ptr), explode_fun_ptr(explode_fun_ptr), lifetime_over_fun_ptr(lifetime_over_fun_ptr) { } /* //USER DEFINED copy-ctor. if it's defined things go crazy BulletFX(const BulletFX& rhs) :data(data),//this line of code seems to do a plain memory-copy without calling the right ctors render_fun_ptr(render_fun_ptr), update_fun_ptr(update_fun_ptr), explode_fun_ptr(explode_fun_ptr), lifetime_over_fun_ptr(lifetime_over_fun_ptr) { } */ }; If i use the user-defined copy-ctor my smart-pointer class goes crazy, and it seems that calling the CopyCtor / assignment operator aren't called as they should. So - does this all make sense ? it seems as if my own copy-ctor of struct BulletFX should do exactly what the compiler-generated would, but it seems to forget to call the right constructors down the chain. compiler bug ? me being stupid ? Sorry about the big code, some small example could have illustrated too. but often you guys ask for the real code, so well - here it is :D EDIT : more info : typedef ParticleId unsigned int; Particle has no user defined copyctor, but has a member of type : Particle { .... Resource<Texture> tex_res; ... } Resource is a smart-pointer class, and has all ctor's defined (also asignment operator) and it seems that Resource is copied bitwise. EDIT : henrik solved it... data(data) is stupid of course ! it should of course be rhs.data !!! sorry for huge amount of code, with a very little bug in it !!! (Guess you shouldn't code at 1 in the morning :D )

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• Generate syntax tree for simple math operations

  - by M28

  I am trying to generate a syntax tree, for a given string with simple math operators (+, -, *, /, and parenthesis). Given the string "1 + 2 * 3": It should return an array like this: ["+", [1, ["*", [2,3] ] ] ] I made a function to transform "1 + 2 * 3" in [1,"+",2,"*",3]. The problem is: I have no idea to give priority to certain operations. My code is: function isNumber(ch){ switch (ch) { case '0': case '1': case '2': case '3': case '4': case '5': case '6': case '7': case '8': case '9': case '.': return true; break; default: return false; break; } } function generateSyntaxTree(text){ if (typeof text != 'string') return []; var code = text.replace(new RegExp("[ \t\r\n\v\f]", "gm"), ""); var codeArray = []; var syntaxTree = []; // Put it in its on scope (function(){ var lastPos = 0; var wasNum = false; for (var i = 0; i < code.length; i++) { var cChar = code[i]; if (isNumber(cChar)) { if (!wasNum) { if (i != 0) { codeArray.push(code.slice(lastPos, i)); } lastPos = i; wasNum = true; } } else { if (wasNum) { var n = Number(code.slice(lastPos, i)); if (isNaN(n)) { throw new Error("Invalid Number"); return []; } else { codeArray.push(n); } wasNum = false; lastPos = i; } } } if (wasNum) { var n = Number(code.slice(lastPos, code.length)); if (isNaN(n)) { throw new Error("Invalid Number"); return []; } else { codeArray.push(n); } } })(); // At this moment, codeArray = [1,"+",2,"*",3] return syntaxTree; } alert('Returned: ' + generateSyntaxTree("1 + 2 * 3"));

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• Use interface between model and view in ASP.NET MVC

  - by Icerman

  Hi, I am using asp.net MVC 2 to develop a site. IUser is used to be the interface between model and view for better separation of concern. However, things turn to a little messy here. In the controller that handles user sign on: I have the following: IUserBll userBll = new UserBll(); IUser newUser = new User(); newUser.Username = answers[0].ToString(); newUser.Email = answers[1].ToString(); userBll.AddUser(newUser); The User class is defined in web project as a concrete class implementing IUser. There is a similar class in DAL implementing the same interface and used to persist data. However, when the userBll.AddUser is called, the newUser of type User can't be casted to the DAL User class even though both Users class implementing the interface (InvalidCastException). Using conversion operators maybe an option, but it will make the dependency between DAL and web which is against the initial goal of using interface. Any suggestions?

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• How do I optimize this postfix expression tree for speed?

  - by Peter Stewart

  Thanks to the help I received in this post: I have a nice, concise recursive function to traverse a tree in postfix order: deque <char*> d; void Node::postfix() { if (left != __nullptr) { left->postfix(); } if (right != __nullptr) { right->postfix(); } d.push_front(cargo); return; }; This is an expression tree. The branch nodes are operators randomly selected from an array, and the leaf nodes are values or the variable 'x', also randomly selected from an array. char *values[10]={"1.0","2.0","3.0","4.0","5.0","6.0","7.0","8.0","9.0","x"}; char *ops[4]={"+","-","*","/"}; As this will be called billions of times during a run of the genetic algorithm of which it is a part, I'd like to optimize it for speed. I have a number of questions on this topic which I will ask in separate postings. The first is: how can I get access to each 'cargo' as it is found. That is: instead of pushing 'cargo' onto a deque, and then processing the deque to get the value, I'd like to start processing it right away. I don't yet know about parallel processing in c++, but this would ideally be done concurrently on two different processors. In python, I'd make the function a generator and access succeeding 'cargo's using .next(). But I'm using c++ to speed up the python implementation. I'm thinking that this kind of tree has been around for a long time, and somebody has probably optimized it already. Any Ideas? Thanks

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• looking to streamline my RSS feed mashup

  - by Mark Cejas

  Hello crafty developers, I have aggregated RSS feeds from various sources with RSSowl, fetching directly from the social mention API. The RSS feeds are categorized into the following major categories: blogs, news, twitter, Q&A and social networking sites. Each major category is nested with a common group of RSS feeds that represent a particular client/brand ontology. Merging these feeds into the RSSowl reader application, allows me to conduct and save refined search queries (from the aggregated data) into a single file - that I can then tag and further segment for analysis. This scheme is utilized for my own research needs and has helped me considerably. However, I find this RSS mashup scheme kinda clumsy, it requires quite a bit of time to initially organize all of the feeds and I would like to be able to do further natural language processing to the data as well as eventually be able to rank the collected list of URL's into some order of media prominence - right I don't want to pay the ridiculous radian6 web analytics fees, when my intuition is telling me that with a bit of 'elbow grease' I can maybe leverage some available resources online to develop a functional low scale web mining application and get some good intelligence from it. I am now starting to learn a little about computer science - my background is in physical science/statistics so is my thinking in the right track? So, I guess I am imagining an application that allows me to query in a refined manner. A manner that allows me to search for keyword combinations, applying AND/OR operators, selectively focus my queries into particular sources - like a collection of blogs or twitter, or social networking communities, then save the results of my queries into a structured format that can then be manipulated and explored. Am I dreaming? I just had to get all of this out. any bit of advice and insight would be hugely appreciated. my best, Mark

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• what is meant by normalization in huge pointers

  - by wrapperm

  Hi, I have a lot of confusion on understanding the difference between a "far" pointer and "huge" pointer, searched for it all over in google for a solution, couldnot find one. Can any one explain me the difference between the two. Also, what is the exact normalization concept related to huge pointers. Please donot give me the following or any similar answers: "The only difference between a far pointer and a huge pointer is that a huge pointer is normalized by the compiler. A normalized pointer is one that has as much of the address as possible in the segment, meaning that the offset is never larger than 15. A huge pointer is normalized only when pointer arithmetic is performed on it. It is not normalized when an assignment is made. You can cause it to be normalized without changing the value by incrementing and then decrementing it. The offset must be less than 16 because the segment can represent any value greater than or equal to 16 (e.g. Absolute address 0x17 in a normalized form would be 0001:0001. While a far pointer could address the absolute address 0x17 with 0000:0017, this is not a valid huge (normalized) pointer because the offset is greater than 0000F.). Huge pointers can also be incremented and decremented using arithmetic operators, but since they are normalized they will not wrap like far pointers." Here the normalization concept is not very well explained, or may be I'm unable to understand it very well. Can anyone try explaining this concept from a beginners point of view. Thanks, Rahamath

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• barebones sort algorithm

  - by user309322

  i have been asked to make a simple sort aglorithm to sort a random series of 6 numbers into numerical order. However i have been asked to do this using "Barebones" a theoretical language put forward in the Book Computer Science an overview. Some information on the language can be found here http://www.brouhaha.com/~eric/software/barebones/ Just to clarify i am a student teacher and have been doing anaysis on "mini-programing languages" and their uses in a teaching environment, i suggested to my tutor that i look at barebones and asked what sort of exmaple program i should write . He suggested a simple sort algorithm. Now since looking at the language i cant understand how i can do this without using arrays and if statements. The code to swap the value of variables would be while a not 0 do; incr Aux1; decr a; end; while b not 0 do; incr Aux2 decr b end; while Aux1 not 0 do; incr a; decr Aux1; end; while Aux2 not 0 do; incr b; decr Aux2; end; however the language does not provide < or operators

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• GCC problem with raw double type comparisons

  - by Monomer

  I have the following bit of code, however when compiling it with GCC 4.4 with various optimization flags I get some unexpected results when its run. #include <iostream> int main() { const unsigned int cnt = 10; double lst[cnt] = { 0.0 }; const double v[4] = { 131.313, 737.373, 979.797, 731.137 }; for(unsigned int i = 0; i < cnt; ++i) { lst[i] = v[i % 4] * i; } for(unsigned int i = 0; i < cnt; ++i) { double d = v[i % 4] * i; if(lst[i] != d) { std::cout << "error @ : " << i << std::endl; return 1; } } return 0; } when compiled with: "g++ -pedantic -Wall -Werror -O1 -o test test.cpp" I get the following output: "error @ : 3" when compiled with: "g++ -pedantic -Wall -Werror -O2 -o test test.cpp" I get the following output: "error @ : 3" when compiled with: "g++ -pedantic -Wall -Werror -O3 -o test test.cpp" I get no errors when compiled with: "g++ -pedantic -Wall -Werror -o test test.cpp" I get no errors I do not believe this to be an issue related to rounding, or epsilon difference in the comparison. I've tried this with Intel v10 and MSVC 9.0 and they all seem to work as expected. I believe this should be nothing more than a bitwise compare. If I replace the if-statement with the following: if (static_cast<long long int>(lst[i]) != static_cast<long long int>(d)), and add "-Wno-long-long" I get no errors in any of the optimization modes when run. If I add std::cout << d << std::endl; before the "return 1", I get no errors in any of the optimization modes when run. Is this a bug in my code, or is there something wrong with GCC and the way it handles the double type?

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• Multiple inequality conditions (range queries) in NoSQL

  - by pableu

  Hi, I have an application where I'd like to use a NoSQL database, but I still want to do range queries over two different properties, for example select all entries between times T1 and T2 where the noiselevel is smaller than X. On the other hand, I would like to use a NoSQL/Key-Value store because my data is very sparse and diverse, and I do not want to create new tables for every new datatype that I might come across. I know that you cannot use multiple inequality filters for the Google Datastore (source). I also know that this feature is coming (according to this). I know that this is also not possible in CouchDB (source). I think I also more or less understand why this is the case. Now, this makes me wonder.. Is that the case with all NoSQL databases? Can other NoSQL systems make range queries over two different properties? How about, for example, Mongo DB? I've looked in the Documentation, but the only thing I've found was the following snippet in their docu: Note that any of the operators on this page can be combined in the same query document. For example, to find all document where j is not equal to 3 and k is greater than 10, you'd query like so: db.things.find({j: {$ne: 3}, k: {$gt: 10} }); So they use greater-than and not-equal on two different properties. They don't say anything about two inequalities ;-) Any input and enlightenment is welcome :-)

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• Visual C++ doesn't operator<< overload

  - by PierreBdR

  I have a vector class that I want to be able to input/output from a QTextStream object. The forward declaration of my vector class is: namespace util { template <size_t dim, typename T> class Vector; } I define the operator<< as: namespace util { template <size_t dim, typename T> QTextStream& operator<<(QTextStream& out, const util::Vector<dim,T>& vec) { ... } template <size_t dim, typename T> QTextStream& operator>>(QTextStream& in,util::Vector<dim,T>& vec) { .. } } However, if I ty to use these operators, Visual C++ returns this error: error C2678: binary '<<' : no operator found which takes a left-hand operand of type 'QTextStream' (or there is no acceptable conversion) A few things I tried: Originaly, the methods were defined as friends of the template, and it is working fine this way with g++. The methods have been moved outside the namespace util I changed the definition of the templates to fit what I found on various Visual C++ websites. The original friend declaration is: friend QTextStream& operator>>(QTextStream& ss, Vector& in) { ... } The "Visual C++ adapted" version is: friend QTextStream& operator>> <dim,T>(QTextStream& ss, Vector<dim,T>& in); with the function pre-declared before the class and implemented after. I checked the file is correctly included using: #pragma message ("Including vector header") And everything seems fine. Doesn anyone has any idea what might be wrong?

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• Any useful suggestions to figure out where memory is being free'd in a Win32 process?

  - by LeopardSkinPillBoxHat

  An application I am working with is exhibiting the following behaviour: During a particular high-memory operation, the memory usage of the process under Task Manager (Mem Usage stat) reaches a peak of approximately 2.5GB (Note: A registry key has been set to allow this, as usually there is a maximum of 2GB for a process under 32-bit Windows) After the operation is complete, the process size slowly starts decreasing at a rate of 1MB per second. I am trying to figure out the easiest way to quickly determine who is freeing this memory, and where it is being free'd. I am having trouble attaching a memory profiler to my code, and I don't particularly want to override the new/delete operators to track the allocations/deallocations (IOW, I want to do this without re-compiling my code). Can anyone offer any useful suggestions of how I could do this via the Visual Studio debugger? Update I should also mention that it's a multi-threaded application, so pausing the application and analysing the call stack through the debugger is not the most desirable option. I considered freezing different threads one at a time to see if the memory stops reducing, but I'm fairly certain this will cause the application to crash.

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• How do I send floats in window messages.

  - by yngvedh

  Hi, What is the best way to send a float in a windows message using c++ casting operators? The reason I ask is that the approach which first occurred to me did not work. For the record I'm using the standard win32 function to send messages: PostWindowMessage(UINT nMsg, WPARAM wParam, LPARAM lParam) What does not work: Using static_cast<WPARAM>() does not work since WPARAM is typedef'ed to UINT_PTR and will do a numeric conversion from float to int, effectively truncating the value of the float. Using reinterpret_cast<WPARAM>() does not work since it is meant for use with pointers and fails with a compilation error. I can think of two workarounds at the moment: Using reinterpret_cast in conjunction with the address of operator: float f = 42.0f; ::PostWindowMessage(WM_SOME_MESSAGE, *reinterpret_cast<WPARAM*>(&f), 0); Using an union: union { WPARAM wParam, float f }; f = 42.0f; ::PostWindowMessage(WM_SOME_MESSAGE, wParam, 0); Which of these are preffered? Are there any other more elegant way of accomplishing this?

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