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• SQL Server 15MM rows, simple COUNT query. 15+ seconds?

  - by john

  We took over a website from another company after a client decided to switch. We have a table that grows by about 25k records a day, and is currently at 15MM records. The table looks something like: id (PK, int, not null) member_id (int, not null) another_id (int, not null) date (datetime, not null) SELECT COUNT(id) FROM tbl can take up to 15 seconds. A simple inner join on 'another_id' takes over 30 seconds. I can't imagine why this is taking so long. Any advice? SQL Server 2005 Express

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• Using popen() to invoke a shell command?

  - by Anvar

  When running the following code through xcode I get inconsistent behavior. Sometimes it prints the git version correctly, other times it doesn't print anything. The return code from the shell command is always 0 though. Any ideas on why this might be? What am I doing wrong? #define BUFFER_SIZE 256 int main (int argc, const char * argv[]) { FILE *fpipe; char *command="/opt/local/bin/git --version"; char line[BUFFER_SIZE]; if ( !(fpipe = (FILE*)popen(command, "r")) ) { // If fpipe is NULL perror("Problems with pipe"); exit(1); } while ( fgets( line, sizeof(char) * BUFFER_SIZE, fpipe)) { // Inconsistent (happens sometimes) printf("READING LINE"); printf("%s", line); } int status = pclose(fpipe); if (status != 0) { // Never happens printf("Strange error code: %d", status); } return 0; }

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• What's the difference between => , ()=>, and Unit=>

  - by Malvolio

  I'm trying to represent a function that takes no arguments and returns no value (I'm simulating the setTimeout function in JavaScript, if you must know.) case class Scheduled(time : Int, callback : => Unit) doesn't compile, saying " `val' parameters may not be call-by-name" case class Scheduled(time : Int, callback : () => Unit) compiles, but has to be invoked strangely, instead of Scheduled(40, { println("x") } ) I have to do this Scheduled(40, { () => println("x") } ) What also works is class Scheduled(time : Int, callback : Unit => Unit) but is invoked in an even-less-sensible way Scheduled(40, { x : Unit => println("x") } ) (What would a variable of type Unit be?) What I want of course is a constructor that can be invoke the way I would invoke it if it were an ordinary function: Scheduled(40, println("x") ) Give baby his bottle!

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• In a C++ template, is it allowed to return an object with specific type parameters?

  - by nieldw

  When I've got a template with certain type parameters, is it allowed for a function to return an object of this same template, but with different types? In other words, is the following allowed? template<class edgeDecor, class vertexDecor, bool dir> Graph<edgeDecor,int,dir> Graph<edgeDecor,vertexDecor,dir>::Dijkstra(vertex s, bool print = false) const { /* Construct new Graph with apropriate decorators */ Graph<edgeDecor,int,dir> span = new Graph<edgeDecor,int,dir>(); /* ... */ return span; }; If this is not allowed, how can I accomplish the same kind of thing?

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• NSString inheritance

  - by Stef

  Hi, I'm doing an useless thing for my first step in Obj-C @interface String : NSString { int m_isnull; } - (id) init; - (int) isNull; @end @implementation String - (id) init { self = [super init]; m_isnull=1; return self; } - (int) isNull { return m_isnull; } @end test : String *a; a=@"ok"; Works fine, but just 2 little questions 1) When I'm compiling I have this warning warning: incompatible Objective-C types assigning 'struct NSString *', expected 'struct String *' I don't know how to avoid it !? 2) a=@"ok" is a fastest way to initialize a string, but when I'm debugging, I don't stop by at my init constructor why ?

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• Getting the fractional part of a float without using modf()

  - by knight666

  Hi, I'm developing for a platform without a math library, so I need to build my own tools. My current way of getting the fraction is to convert the float to fixed point (multiply with (float)0xFFFF, cast to int), get only the lower part (mask with 0xFFFF) and convert it back to a float again. However, the imprecision is killing me. I'm using my Frac() and InvFrac() functions to draw an anti-aliased line. Using modf I get a perfectly smooth line. With my own method pixels start jumping around due to precision loss. This is my code: const float fp_amount = (float)(0xFFFF); const float fp_amount_inv = 1.f / fp_amount; inline float Frac(float a_X) { return ((int)(a_X * fp_amount) & 0xFFFF) * fp_amount_inv; } inline float Frac(float a_X) { return (0xFFFF - (int)(a_X * fp_amount) & 0xFFFF) * fp_amount_inv; } Thanks in advance!

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• Writing array to text file

  - by user3661876

  I have an array, but it won't write each index to the text file. Instead it is only writing the last index and the other indexes are not appearing. Can anyone help me to get the entire array printed to the text file? static void solve(int k) { if (k == N) // We placed N-1 queens (0 included), problem solved! { // Solution found! using (StreamWriter sw = new StreamWriter("names.txt")) { Console.Write("Solution: "); for (int i = 0; i < N; i++) { Console.Write(position[i] + " "); foreach (int s in position[i].ToString()) { string list = position[i].ToString(); sw.Write(list + " "); } } Console.WriteLine(); sum += 1; } }

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• array of objects of a class

  - by anurag18294

  #include class test{ int a; char b; public: test() { cout<<"\n\nDefault constructor being called"; } test(int i,char j) { a=i; b=j; cout<<"\n\nConstructor with arguments called"; } }; int main() { test tarray[5]; test newobj(31,'z'); }; In the above code snippet can we intialize values to tarray[5].

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• Missing MethodInfo for overloaded function with different return type

  - by Charvak

  I have a class defined as follows interface ITest { List<T> Find<T>(int i); } class Test: ITest { public T List<T> Find<T>(int i) { return default(T); } List<T> ITest.Find<T>(int i) { return null; } } When I use typeof(Test).GetMethods() (both with and without appropriate BindingFlags) I do not get the MethodInfo for ITest.Find function. What is the best way of getting the MethodInfo for the missing method? Thanks

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• Python - multi-line array

  - by Ockonal

  Hi guys, in c++ I can wrote: int someArray[8][8]; for (int i=0; i < 7; i++) for (int j=0; j < 7; j++) someArray[i][j] = 0; And how can I initialize multi-line arrays in python? I tried: array = [[],[]] for i in xrange(8): for j in xrange(8): array[i][j] = 0

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• Writing different structs to a file in C++? [on hold]

  - by user58053

  I need a way to write structures of three different kinds to a binary file, which later has to be searched. (As in, for example, struct A has two fields, an int and a char; struct B has int and a long; I need to output all structures whose int equals the one given from keyboard). I understand how to write structs of the same kind to a file and how to search them, but here I am just lost, best thing I came up with is declaring a struct containing all possibly needed fields and leaving the ones I don't need empty, but it really feels wrong, there HAS to be a better way to do that. I've read about binary files and could not find anything relevant, most examples and tutorials deal with writing one data type. Could anyone point me in the right direction? EDIT: I am looking for what @Jerry_coffin called database mode, and will probably use one of the existing database systems for that, best way to go, probably. Thank you everybody for the suggestions

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• Is a Critical Section around an integer getter and setter redundant?

  - by Tim Gradwell

  Do critical sections inside trivial int accessors actually do anything useful? int GetFoo() { CriticalSection(crit_id); return foo; } void SetFoo(int value) { CriticalSection(crit_id); foo = value; } Is it possible for two threads to be attempting to read and write foo simultaneously? I'd have thought 'no' unless integers are written byte-at-a-time, in which case I can see the use. But I'd have though modern cpus would read/write integers in a single atomic action...

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• ArrayIndexOutOfBound exception even though I check for array length!

  - by xtracto

  I have the following code in some app: int lowRange=50; int[] ageRangeIndividual = {6, 10, 18, 25, 45, 65, 90}; int index=0; for (; index<ageRangeIndividual.length-1 && ageRangeIndividual[index]<=lowRange;index++); I am getting an "Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 7" in the for line! even though I explicitly specify to break the cycle if index < last indexable item in the array! This does not happen always, but after some time of running said program (lowRange varies each time the function is called) What am I not seeing?

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• Read text and print each (byte) character in separate line

  - by user2967663

  preforming this code to read file and print each character \ (byte) in separate line works well with ASCII void preprocess_file (FILE *fp) { int cc; for (;;) { cc = getc (fp); if (cc == EOF) break; printf ("%c\n", cc); } } int main(int argc, char *argv []) { preprocess_file (stdin); exit (0); } but when i use it with UTF-8 encoded text it shows unredable character such as ï » ? ? § ? „ ? … ? ¤ ? ´ ? and advice ? Thanks

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• string reverse without new array

  - by Codeguru

  hi can anybody tell me the error in this? #include<stdio.h> int main() { char a[]="abcdefgh"; int i=0; int n=strlen(a); char *first; char *second; char *c; *first=a[0]; *second=a[7]; for(i=0;i<=n/2;i++) { *c=*first; *first=*second; *second=*c; first++; second--; } for(i=0;i<=7;i++) { printf("%c",a[i]); } }

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• to store char* from function return value

  - by samprat

  Hi folks, I am trying to implement a function which reads from Serial Port ( Linux) and retuns char*. The function works fine but how would I store return value from function. example of function is char *ReadToSerialPort() { char *bufptr; char buffer[256]; // Input buffer/ / //char *bufptr; // Current char in buffer // int nbytes; // Number of bytes read // bufptr = buffer; while ((nbytes = read(fd, bufptr, buffer+sizeof(buffer)-bufptr -1 )) > 0) { bufptr += nbytes; // if (bufptr[-1] == '\n' || bufptr[-1] == '\r') /*if ( bufptr[sizeof(buffer) -1] == '*' && bufptr[0] == '$' ) { break; }*/ } // while ends if ( nbytes ) return bufptr; else return 0; *bufptr = '\0'; } // end ReadAdrPort //In main int main( int argc , char *argv[]) { char *letter; if(strcpy(letter, ReadToSerialPort()) >0 ) { printf("Response is %s\n",letter); } }

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• question regarding "this" pointer in c++

  - by sil3nt

  hello there, i have been given class with int variables x and y in private, and an operator overload function, class Bag{ private: int x; int y; public: Bag(); ~Bag(); //....... //.....etc }; Bag operator+ (Bag new) const{ Bag result(*this); //what does this mean? result.x += new.x; result.y += new.y; } What is the effect of having "Bag result(*this);" there?.

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• Strange macro declaration in C

  - by Andrey Atapin

  Exploring libusb-1.0.9 source code, I have found such line (./os/poll_windows.c:78): #define CHECK_INIT_POLLING do {if(!is_polling_set) init_polling();} while(0) As for me this is the same like: #define CHECK_INIT_POLLING if(!is_polling_set) init_polling(); Is there any reason to loop that expression? UPDATE: I couldn't still realize what'd be wrong after the answers, and the following example helped: #include <stdio.h> #define TEST if(test) foo(); #define TEST_DO do { if(test) foo(); } while(0) int test = 1; void foo() { printf("%s", "Foo called"); } int main(int argc, char** argv) { if(argc > 1) TEST_DO; /* LINE 12 */ else printf("%s", "skipping..."); return 0; } If you put TEST at line 12, a compiler will give an error "error: ‘else’ without a previous ‘if’". Hope, this will help someone.

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• C++ putting a 2d array of floats into a char*

  - by sam

  Hello, I'm trying to take a 2d vector of floats (input) and put them into a char* (output) in c++. void foo(const std::vector<std::vector<float> > &input, char* &output ) { char charBuf[sizeof(output)]; int counter = 0; for(unsigned int i=0; i<input.size(); i++) { for(unsigned int p=0; p<input.at(i).size(); p++) { //what the heck goes here } }

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• What is the problem with this code?

  - by eSKay

  #include<stdio.h> class A { public: int a;}; class B: public A { public: static int b; B(){ b++; printf("B:%d\n",b); } }; int main() { A* a1 = new B[100]; A* a2 = new B(); return 0; } Error: In function `main': undefined reference to `B::b' undefined reference to `B::b' undefined reference to `B::b' undefined reference to `B::b'

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• Improve C function performance with cache locality?

  - by Christoper Hans

  I have to find a diagonal difference in a matrix represented as 2d array and the function prototype is int diagonal_diff(int x[512][512]) I have to use a 2d array, and the data is 512x512. This is tested on a SPARC machine: my current timing is 6ms but I need to be under 2ms. Sample data: [3][4][5][9] [2][8][9][4] [6][9][7][3] [5][8][8][2] The difference is: |4-2| + |5-6| + |9-5| + |9-9| + |4-8| + |3-8| = 2 + 1 + 4 + 0 + 4 + 5 = 16 In order to do that, I use the following algorithm: int i,j,result=0; for(i=0; i<4; i++) for(j=0; j<4; j++) result+=abs(array[i][j]-[j][i]); return result; But this algorithm keeps accessing the column, row, column, row, etc which make inefficient use of cache. Is there a way to improve my function?

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• what's wrong with my one-liner strncpy: while(*s++ = *t++ && n-- > 0);?

  - by pvd

  #include <stdio.h> #define STR_BUF 10000 #define STR_MATCH 7 void mystrncpy(char* s, char* t, int n) { while(*s++ = *t++ && n-- > 0); } int main() { int result; char str_s[STR_BUF] = "not so long test string"; char buf_1[STR_BUF]; mystrncpy(buf_1, str_s, STR_MATCH); printf ("buf_1 (mystrncpy, 7 chars): %s\n", buf_1); return 0; } When I run it, nothing happened ian@ubuntu:~/tmp$ gcc myncpy.c -o myn&&./myn buf_1 (mystrncpy, 7chars):

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• conversions in C++

  - by lego69

  I have this snippet of the code: header class A { private: int player; public: A(int initPlayer = 0); A(const A&); A& operator=(const A&); ~A(); void foo() const; friend A& operator=(A& i, const A& member); }; operator= A& operator=(A& i, const A& member){ i(member.player); return i; } and I have row in my code: i = *pa1; A *pa1 = new A(a2); at the beginning i was int how can I fix it, thanks in advance I have an error must be non-static function

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• c++: at what point should I start using "new char[N]" vs a static buffer "char[Nmax]"

  - by dan

  My question is with regard to C++ Suppose I write a function to return a list of items to the caller. Each item has 2 logical fields: 1) an int ID, and 2) some data whose size may vary, let's say from 4 bytes up to 16Kbytes. So my question is whether to use a data structure like: struct item { int field1; char field2[MAX_LEN]; OR, rather, to allocate field2 from the heap, and require the caller to destroy when he's done: struct item{ int field1; char *field2; // new char[N] -- destroy[] when done! Since the max size of field #2 is large, is makes sense that this would be allocated from the heap, right? So once I know the size N, I call field2 = new char[N], and populate it. Now, is this horribly inefficient? Is it worse in cases where N is always small, i.e. suppose I have 10000 items that have N=4?

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• base pointer to derived class

  - by Jay

  Suppose there are Base class and Derived class. Base *A = new Base; Here A is a pointer point to Base class, and new constructs one that A points to. I also saw Base *B = new Derived; How to explain this? B is a pointer to Base Class, and a Derived class constructed and pointed by B? If there is a function derived from Base class, say, Virtual void f(), and it's been overridden in Derived class, then B->f() will invoke which version of the function? version in Base class, or version that overridden in Derived Class. What if there is a new function void g()in Derived, is B->g() going to invoke this function properly? One more is, is int *a = new double; or int *a = new int; legal?

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