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Conceptual data modeling: Is RDF the right tool? Other solutions?

- by paprika

I'm planning a system that combines various data sources and lets users do simple queries on these. A part of the system needs to act as an abstraction layer that knows all connected data sources: the user shouldn't [need to] know about the underlying data "providers". A data provider could be anything: a relational DBMS, a bug tracking system, ..., a weather station. They are hooked up to the query system through a common API that defines how to "offer" data. The type of queries a certain data provider understands is given by its "offer" (e.g. I know these entities, I can give you aggregates of type X for relationship Y, ...). My concern right now is the unification of the data: the various data providers need to agree on a common vocabulary (e.g. the name of the entity "customer" could vary across different systems). Thus, defining a high level representation of the entities and their relationships is required. So far I have the following requirements: I need to be able to define objects and their properties/attributes. Further, arbitrary relations between these objects need to be represented: a verb that defines the nature of the relation (e.g. "knows"), the multiplicity (e.g. 1:n) and the direction/navigability of the relation. It occurs to me that RDF is a viable option, but is it "the right tool" for this job? What other solutions/frameworks do exist for semantic data modeling that have a machine readable representation and why are they better suited for this task? I'm grateful for every opinion and pointer to helpful resources.

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So, I guess I can't use "&&" in the Python if conditional. What should I use in this case? Any help?

- by Sergio Tapia

Here's my code: # F. front_back # Consider dividing a string into two halves. # If the length is even, the front and back halves are the same length. # If the length is odd, we'll say that the extra char goes in the front half. # e.g. 'abcde', the front half is 'abc', the back half 'de'. # Given 2 strings, a and b, return a string of the form # a-front + b-front + a-back + b-back def front_back(a, b): # +++your code here+++ if len(a) % 2 == 0 && len(b) % 2 == 0: return a[:(len(a)/2)] + b[:(len(b)/2)] + a[(len(a)/2):] + b[(len(b)/2):] else: #todo! Not yet done. :P return I'm getting an error in the IF conditional. What am I doing wrong? Edit: I meant no arrogance here. Someone edited my question title to make it sound douchy. I was genuinely confused about what to use, didn't think 'and' would be a keyword. Please don't downvote as other newbies might be confused about it as well.

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Optimal (Time paradigm) solution to check variable within boundary

- by kumar_m_kiran

Hi All, Sorry if the question is very naive. I will have to check the below condition in my code 0 < x < y i.e code similar to if(x > 0 && x < y) The basic problem at system level is - currently, for every call (Telecom domain terminology), my existing code is hit (many times). So performance is very very critical, Now, I need to add a check for boundary checking (at many location - but different boundary comparison at each location). At very normal level of coding, the above comparison would look very naive without any issue. However, when added over my statistics module (which is dipped many times), performance will go down. So I would like to know the best possible way to handle the above scenario (kind of optimal way for limits checking technique). Like for example, if bit comparison works better than normal comparison or can both the comparison be evaluation in shorter time span? Other Info x is unsigned integer (which must be checked to be greater than 0 and less than y). y is unsigned integer. y is a non-const and varies for every comparison. Here time is the constraint compared to space. Language - C++. Now, later if I need to change the attribute of y to a float/double, would there be another way to optimize the check (i.e will the suggested optimal technique for integer become non-optimal solution when y is changed to float/double). Thanks in advance for any input. PS : OS used is SUSE 10 64 bit x64_64, AIX 5.3 64 bit, HP UX 11.1 A 64.

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multiple dependent android projects in eclipse

- by lope

Hi there! I just started to play with android dev and java+eclipse is pretty new to me. I managed to create simple project and run it on my device. Now I want to create simple game (more of them actually) and I would love to use shared code base for all of them (game loop, initialization, etc..). Problem is that I have no idea how to correctly do this. I created android project called engine with all basic stuff that I need and made it work on device. Now I tried to create another project in same workspace called mygame. Main class (activity) of mygame is MyGameApp which inherits from EngineApp (main activity of my engine project) which inherits from Activity. I added engine project into required projects in mygame build path tab in properties. Problem is that when I try to run this project it crashes on ClassNotFoundException trying to find my MyGameApp class. Any help (or pointer to some articles that explain how this is done) is greatly appreciated. few hours of googling didn't help much :/

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compilation error

- by Bond

#include<dirent.h> #include<stdio.h> #include<stdlib.h> #include<sys/stat.h> int main () { struct dirent **namelist; int i,j; char userd[20]; struct stat statBuf; printf("Enter a directory %s\n",userd); scanf("%s",&userd); printf("the dir is %s\n",*userd); i=scandir(".",&namelist,0,alphasort); printf("enter a directory name %s",*userd); printf("scandir returned i=%d\n",&i); if (i<0) perror("Scandir failed to open directory I hope you understand \n"); else { for(j=0;j<i;j++) { printf("j=%d i=%d %s\n",j,i,namelist[j]->d_name); // lstat free(namelist[j]); } } free(namelist); } Can some one help to understand why am I getting warning in above code?

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php parsing csv with ftell

- by Robert82

I have a 500mb csv file with over 500,000 lines, each with 80 fields. I am using fget to process the file line by line. $col1 = array(); while (($row = fgetcsv($handle, 1000, ",")) !== FALSE) { $col1[] = $row[0]; } Because of an execution time limit on the PHP file by my hosting provider (120 seconds), I can't process the whole file in one run. I tried using ftell() and fseek() to remember the last position for restart. The trouble is, sometimes the ftell() position is in the middle of a row, and resuming means missing the first half of the row. Is there an elegant way to know the last line successfully processed, and resume from the one after it? I realize I can do a simple counter, and then loop through to that point again, but that would produce diminishing returns on the rows I can process towards the end of the file. Is there something like ftell() and fseek() that would work in my case? Or a way to limit ftell() to return the pointer for the end of the previous line?

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Sqlite3 INSERT INTO Question × 377

- by user316717

Hi, My 1st post. I am creating an exercise app that will record the weight used and the number of "reps" the user did in 4 "Sets" per day over a period of 7 days so the user may view their progress. I have built the database table named FIELDS with 2 columns ROW and FIELD_DATA and I can use the code below to load the data into the db. But the code has a sql statement that says, INSERT OR REPLACE INTO FIELDS (ROW, FIELD_DATA)VALUES (%d, '%@'); When I change the statment to: INSERT INTO FIELDS (ROW, FIELD_DATA)VALUES (%d, '%@'); Nothing happens. That is no data is recorded in the db. Below is the code: #define kFilname @"StData.sqlite3" - (NSString *)dataFilePath { NSArray *paths = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; return [documentsDirectory stringByAppendingPathComponent:kFilname]; } -(IBAction)saveData:(id)sender; { for (int i = 1; i <= 8; i++) { NSString *fieldName = [[NSString alloc]initWithFormat:@"field%d", i]; UITextField *field = [self valueForKey:fieldName]; [fieldName release]; NSString *insert = [[NSString alloc] initWithFormat: @"INSERT OR REPLACE INTO FIELDS (ROW, FIELD_DATA) VALUES (%d, '%@');",i, field.text]; // sqlite3_stmt *stmt; char *errorMsg; if (sqlite3_exec (database, [insert UTF8String], NULL, NULL, &errorMsg) != SQLITE_OK) { // NSAssert1(0, @"Error updating table: %s", errorMsg); sqlite3_free(errorMsg); } } sqlite3_close(database); } So how do I modify the code to do what I want? It seemed like a simple sql statement change at first but obviously there must be more. I am new to Objective-C and iPhone programming. I am not new to using sql statements as I have been creating web apps in ASP for a number of years. Any help will be greatly appreciated, this is driving me nuts! Thanks in advance Dave

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pass parameter from $.post() callback to outer variable

- by Nazmin

basically i want to hold a parameter that retrieve value from $.post() call like this: init = function(){ var lastpage = getLastPage(); } function getLastPage(){ $.post("getInfo.php",{ last: "yes" }, function(data){ setLast(data.last); },'json'); return function setLast(data){ return data; } } so when reach at last post (last page) i should check with lastpage variable that has a value returned from getLastPage() function. I'm pretty blur with javascript pointer and all. Please help guys. update (20/4/2010): I've done the other way around, like this: init = function(){ getLastPage(); if((page+1) == $("#lastpage").val()){ alert("this is last post"); }else{ page++; //get info and display to the page here } } function getLastPage(){ $.post("getInfo.php",{ last: "yes" }, function(data){ $("#lastpage").val(data.last); },'json'); } first run the function to temporarily store the value in hidden input tag (lastpage) and then grab the value again to check it whenever i click forward button. if you all have more appropriate way please tell me.

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Qt - 2 QMainWindow glued - Size of Layout

- by user1773603

I have a main window that I center this way in main.cpp : int main(int argc, char *argv[]) { QApplication app(argc, argv); QMainWindow *qmain = new QMainWindow; Ui_MainWindow ui; ui.setupUi(qmain); QRect r = qmain->geometry(); r.moveCenter(QApplication::desktop()->availableGeometry().center()); qmain->setGeometry(r); qmain->show(); return app.exec(); } In this "qmain" main window, I can create another QMainWindow and I try to make stick (or glue I don't know how to say) the two windows. Actually, I would like the right-top corner of the first one to be located at the left-top of the second one. For this, I use the following Ui_MainWindow's member function : void Ui_MainWindow::generate_IC() { qmenu = new QMainWindow; DiskMenu = new Ui_DiskGalMenu; DiskMenu->setupUi(qmenu); setInitialDiskMenuPosition(qmenu, this); qmenu->show(); } and the setInitialDiskMenuPosition : void Ui_MainWindow::setInitialDiskMenuPosition(QMainWindow *MainWindow, Ui_MainWindow *parent) { QSize size = parent->widget->size(); QDesktopWidget* desktop = QApplication::desktop(); int width = desktop->width(); int height = desktop->height(); int mw = size.width(); int mh = size.height(); int right = (width/2) + (mw/2); int top = (height/2) - (mh/2); MainWindow->move(right, top); } But the problem is that I don't get exactly what I want since the centralwidget size "parent- widget-size()" only returns the size of the widget and not the whole "qmain" parent window. So I have a light shift because the borders of the "qmain" window are not taken in account like it is shown below : If I could have access to the size of the whole parent window... If anyone could help me

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Common Properties: Consolidating Loan, Purchase, Inventory and Sale tables into one Transaction tabl

- by Frank Computer

Pawnshop Application: I have separate tables for Loan, Purchase, Inventory & Sales transactions. Each tables rows are joined to their respective customer rows by: customer.pk [serial] = loan.fk [integer]; = purchase.fk [integer]; = inventory.fk [integer]; = sale.fk [integer]; Since there are so many common properties within the four tables, I consolidated the four tables into one table called "transaction", where a column: transaction.trx_type char(1) {L=Loan, P=Purchase, I=Inventory, S=Sale} Scenario: A customer initially pawns merchandise, makes a couple of interest payments, then decides he wants to sell the merchandise to the pawnshop, who then places merchandise in Inventory and eventually sells it to another customer. I designed a generic transaction table where for example: transaction.main_amount DECIMAL(7,2) in a loan transaction holds the pawn amount, in a purchase holds the purchase price, in inventory and sale holds sale price. This is clearly a denormalized design, but has made programming alot easier and improved performance. Any type of transaction can now be performed from within one screen, without the need to change to different tables.

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When are temporaries created as part of a function call destroyed?

- by Michael Mrozek

Is a temporary created as part of an argument to a function call guaranteed to stay around until the called function ends, even if the temporary isn't passed directly to the function? There's virtually no chance that was coherent, so here's an example: class A { public: A(int x) : x(x) {printf("Constructed A(%d)\n", x);} ~A() {printf("Destroyed A\n");} int x; int* y() {return &x;} }; void foo(int* bar) { printf("foo(): %d\n", *bar); } int main(int argc, char** argv) { foo(A(4).y()); } If A(4) were passed directly to foo it would definitely not be destroyed until after the foo call ended, but instead I'm calling a method on the temporary and losing any reference to it. I would instinctively think the temporary A would be destroyed before foo even starts, but testing with GCC 4.3.4 shows it isn't; the output is: Constructed A(4) foo(): 4 Destroyed A The question is, is GCC's behavior guaranteed by the spec? Or is a compiler allowed to destroy the temporary A before the call to foo, invaliding the pointer to its member I'm using?

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Is this an error in "More Effective C++" in Item28?

- by particle128

I encountered a question when I was reading the item28 in More Effective C++ .In this item, the author shows to us that we can use member template in SmartPtr such that the SmartPtr<Cassette> can be converted to SmartPtr<MusicProduct>. The following code is not the same as in the book,but has the same effect. #include <iostream> class Base{}; class Derived:public Base{}; template<typename T> class smart{ public: smart(T* ptr):ptr(ptr){} template<typename U> operator smart<U>() { return smart<U>(ptr); } ~smart(){delete ptr;} private: T* ptr; }; void test(const smart<Base>& ) {} int main() { smart<Derived> sd(new Derived); test(sd); return 0; } It indeed can be compiled without compilation error. But when I ran the executable file, I got a core dump. I think that's because the member function of the conversion operator makes a temporary smart, which has a pointer to the same ptr in sd (its type is smart<Derived>). So the delete directive operates twice. What's more, after calling test, we can never use sd any more, since ptr in sd has already been delete. Now my questions are : Is my thought right? Or my code is not the same as the original code in the book? If my thought is right, is there any method to do this? Thanks very much for your help.

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Why this doesnt't work in C++?

- by user3377450

I'm doing something and I have this: //main.cpp file template<typename t1, typename t2> std::ostream& operator<<(std::ostream& os, const std::pair<t1, t2>& pair) { return os << "< " << pair.first << " , " << pair.second << " >"; } int main() { std::map<int, int> map = { { 1, 2 }, { 2, 3 } }; std::cout << *map.begin() << std::endl;//This works std::copy(map.begin(), map.end(), std::ostream_iterator<std::pair<int,int> >(std::cout, " "));//this doesn't work } I guess this is not working because in the std::copy algorithm the operator isn't defined, but what can I do?

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Why does this CSS button mess with <a> tags?

- by Ian McCullough

Here is my CSS button { border: 0 none; cursor: pointer; padding: 0 15px 0 0; text-align: center; height: 30px; line-height: 30px; width: auto; } button a { color:white; text-decoration:none; } button.rounded { background: transparent url(/images/button/btn_right.png) no-repeat scroll right top; clear: left; font-size: 0.8em; } button span { display: block; padding: 0 0 0 15px; position: relative; white-space: nowrap; height: 30px; line-height: 30px; } button.rounded span { background: transparent url(/images/button/btn_left.png) no-repeat scroll left top; color: #FFFFFF; } button.rounded:hover { background-position: 100% -30px; } button.rounded:hover span { background-position: 0% -30px; } button::-moz-focus-inner { border: none; } Here is the code for my "button" with a link in it. <button class="rounded"><span><a href="profile.php">Profile</a></span></button> The issue is it does not link to the href when i click on it. Anyone know why?

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when will come the new C++ standard? C++0x

- by Oops

Hi, when will the new C++ standard became official? C++ was standardized in 1998 and the standard is called C++98 the C++ standard was updated in 2003 and is called C++03 so the unofficial name "C++0x" lead us to the wrong conclusion that it will come within the first decade of the 20th century. Have u also mentioned that we all make the year 2000 bug again? Now we have 2010 so if you take the X as the latin sign for 10 it should come out this year. But no, also this would be wrong. The answer: The name of the language was always part of the language itself. As we all know the ++ operator means: one more But we have learned in some situations it would be better to write ++C so the other way around often is better. and what does the characters 0x mean in the C++ language? Right it's the prefix for a hexadecimal number. Now the question is easy to answer, it's meaning is: 0x++C int main(){ std::cout << "When will the new C++ standard come out? " << std::endl; int x0_ = 0x7D0, _0x = x0_, C = 0xC, Y1 = C+++_0x, Y2 = x0_+++C; std::cout << "it will be standardized between the Years: " << Y1 << " and " << Y2 << std::endl; char c; std::cin >> c; return 0; } do you agree? regards Oops

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How to make smooth movements in OpenGL?

- by thyrgle

So this kind of on topic to my other OpenGL question (not my OpenGL ES question but OpenGL the desktop version). If you have someone press a key to move a square how do you make the square movement naturally and less jumpy but also at the same speed I have it now? This is my code for the glutKeyboardFunc() function: void handleKeypress(unsigned char key, int x, int y) { if (key == 'w') { for (int i = 0; i < 12; i++) { if (i == 1 || i == 7 || i == 10 || i == 4) { square[i] = square[i] + 1; } } glutPostRedisplay(); } if (key == 'd') { for (int i = 0; i < 12; i++) { if (i == 0 || i % 3 == 0) { square[i] = square[i] + 1; } } glutPostRedisplay(); } if (key == 's') { for (int i = 0; i < 12; i++) { if (i == 1 || i == 7 || i == 10 || i == 4) { square[i] = square[i] - 1; } } glutPostRedisplay(); } if (key == 'a') { for (int i = 0; i < 12; i++) { if (i == 0 || i % 3 == 0) { square[i] = square[i] - 1; } } glutPostRedisplay(); } } I'm sorry if this doesn't quite make sense I'll try to rephrase it in a better way if it doesn't make sense.

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Determining difference in timestamps for two values in the same MySQL table

- by JayRizzo03

I am relatively new to programming in PHP, so I apologize if this is a rather simple question. I have a MySQL database table called MachineReports that contains the following values: ReportNum(primary key, auto increment), MachineID and Timestamp Here is some example data: |ReportNum | MachineID | Timestamp | |1 | AD3203 | 2012-11-18 06:32:28| |2 | AD3203 | 2012-11-19 04:00:15| |3 | BC4300 | 2012-11-19 04:00:15| What I am attempting to do is find the difference in timestamps in seconds for each machine ID by iterating over each row set. I am getting stuck on the best way to do this, however. Here is the code I've written so far: <?php include '../dbconnect/dbconnect.php'; $machineID=[]; //Get a list of all MachineIDs in the database foreach($dbh->query('SELECT DISTINCT(MachineID) FROM MachineReports') as $row) { array_push($machineID, $row[0]); } for($i=0;$i<count($machineID);$i++){ foreach($dbh->query("SELECT MachineID FROM MachineReports WHERE MachineID='$machineID[$i]' ORDER BY MachineID") as $row) { //code to associate each machineID with two time stamps goes here } } ? This code just lists out the contents of the table row by row. My ultimate goal is to find the difference in timestamps for a certain MachineID. One of the things I've considered is using a multidimensional array in php - using the $machineID as the key and then storing the timestamp inside the array the key points to. However, I'm uncertain how to do that since my query parses row by row. I have quite a few questions. 1) Is this the most efficient way to be doing this? I suspect my database table design may not be the best. 2)What would be the best way to determine the difference in timestamps for a certain machineID? Even just a pointer to a topic that would prompt me to think about this in a different way would be helpful - I'm not afraid to do research. Thanks!

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Compression Program in C

- by Delandilon

I want to compress a series of characters. For example if i type Input : FFFFFBBBBBBBCCBBBAABBGGGGGSSS (27 x 8 bits = 216 bits) Output: F5B7C2B3A2B2G5S3 (14 x 8 bits = 112bits) So far this is what i have, i can count the number of Characters in the Array. But the most important task is to count them in the same sequence. I can't seem to figure that out :( Ive stared doing C just a few weeks back, i have knowledge on Array, pointers, ASCII value but in any case can't seem to count these characters in a sequence. Ive try a bit of everything. This approach is no good but it the closest i came to it. #include <stdio.h> #include <conio.h> int main() { int charcnt=0,dotcnt=0,commacnt=0,blankcnt=0,i, countA, countB; char str[125]; printf("*****String Manipulations*****\n\n"); printf("Enter a string\n\n"); scanf("%[^'\n']s",str); printf("\n\nEntered String is \" %s \" \n",str); for(i=0;str[i]!='\0';i++) { // COUNTING EXCEPTION CHARS if(str[i]==' ') blankcnt++; if(str[i]=='.') dotcnt++; if(str[i]==',') commacnt++; if (str[i]=='A' || str[i]=='a') countA++; if (str[i]=='B' || str[i]=='b') countA++; } //PRINT RESULT OF COUNT charcnt=i; printf("\n\nTotal Characters : %d",charcnt); printf("\nTotal Blanks : %d",blankcnt); printf("\nTotal Full stops : %d",dotcnt); printf("\nTotal Commas : %d\n\n",commacnt); printf("A%d\n", countA); }

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Sending a message to nil?

- by Ryan Delucchi

As a Java developer who is reading Apple's Objective-C 2.0 documentation: I wonder as to what sending a message to nil means - let alone how it is actually useful. Taking an excerpt from the documentation: There are several patterns in Cocoa that take advantage of this fact. The value returned from a message to nil may also be valid: If the method returns an object, any pointer type, any integer scalar of size less than or equal to sizeof(void*), a float, a double, a long double, or a long long, then a message sent to nil returns 0. If the method returns a struct, as defined by the Mac OS X ABI Function Call Guide to be returned in registers, then a message sent to nil returns 0.0 for every field in the data structure. Other struct data types will not be filled with zeros. If the method returns anything other than the aforementioned value types the return value of a message sent to nil is undefined. Has Java rendered my brain incapable of grokking the explanation above? Or is there something that I am missing that would make this as clear as glass? Note: Yes, I do get the idea of messages/receivers in Objective-C, I am simply confused about a receiver that happens to be nil.

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Why is the operation address incremented by two?

- by Gavin Jones

I am looking at a Javascript emulator of a NES to try and understand how it works. On this line: addr = this.load(opaddr+2); The opcode is incremented by two. However, the documentation (see appendix E) I'm reading says: Zero page addressing uses a single operand which serves as a pointer to an address in zero page ($0000-$00FF) where the data to be operated on can be found. By using zero page addressing, only one byte is needed for the operand, so the instruction is shorter and, therefore, faster to execute than with addressing modes which take two operands. An example of a zero page instruction is AND $12. So if the operand's argument is only one byte, shouldn't it appear directly after it, and be + 1 instead of + 2? Why +2? This is how I think it works, which may be incorrect. Suppose our memory looks like: ------------------------- | 0 | 1 | 2 | 3 | 4 | 5 | <- index ------------------------- | a | b | c | d | e | f | <- memory ------------------------- ^ \ PC and our PC is 0, pointing to a. For this cycle, we say that the opcode: var pc= 0; //for example's sake var opcode= memory[pc]; //a So shouldn't the first operand be the next slot, i.e. b? var first_operand = memory[pc + 1]; //b

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Help with string equality in Java

- by annayena

The following function accepts 2 strings, the 2nd (not 1st) possibly containing *'s (asterisks). An * is a replacement for a string (empty, 1 char or more), it can appear appear (only in s2) once, twice, more or not at all, it cannot be adjacent to another * (ab**c), no need to check that. public static boolean samePattern(String s1, String s2) It returns true if strings are of the same pattern. It must be recursive, not use any loops, static or global variables. Also it's prohibited to use the method equals in the String class. Can use local variables and method overloading. Can use only these methods: charAt(i), substring(i), substring(i, j), length(). Examples: 1: TheExamIsEasy; 2: "The*xamIs*y" ---> true 1: TheExamIsEasy; 2: "Th*mIsEasy*" ---> true 1: TheExamIsEasy; 2: "*" ---> true 1: TheExamIsEasy; 2: "TheExamIsEasy" ---> true 1: TheExamIsEasy; 2: "The*IsHard" ---> FALSE I am stucked on this question for many hours now! I need the solution in Java please kindly help me.

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Rotating bits of any integer in C

- by Tim

Pass a integer 2 to this function and then return a integer which is 4 x = 2; x = rotateInt('L', x, 1); (left shift the bits by 1) Example: 00000010 - rotate left by 1 - 00000100 but if I pass this: x = rotateInt('R', x, 3); it will return 64, 01000000 Here is the code, can someone correct the error... thanks int rotateInt(char direction, unsigned int x, int y) { unsigned int mask = 0; int num = 0, result = 0; int i; for(i = 0; i < y; i++) { if(direction == 'R') { if((x & 1) == 1) x = (x ^ 129); else x = x >> 1; } else if(direction == 'L') { if((x & 128) == 1) x = (x ^ 129); else x = x << 1; } } result = (result ^ x); return result; }

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How do virtual destructors work?

- by Jack

I am using gcc. I am aware how the virtual destructors solve the problem when we destroy a derived class object pointed by a base class pointer. I want to know how do they work? class A { public: A(){cout<<"A constructor"<<endl;} ~A(){cout<<"A destructor"<<endl;} }; class B:public A { public: B(){cout<<"B constructor"<<endl;} ~B(){cout<<"B destructor"<<endl;} }; int main() { A * a = new B(); delete a; getch(); return 0; } When I change A's destructor to a virtual function, the problem is solved. What is the inner working for this. Why do I make A's destructor virtual.

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SQL Server: Why use shorter VARCHAR(n) fields?

- by chryss

It is frequently advised to choose database field sizes to be as narrow as possible. I am wondering to what degree this applies to SQL Server 2005 VARCHAR columns: Storing 10-letter English words in a VARCHAR(255) field will not take up more storage than in a VARCHAR(10) field. Are there other reasons to restrict the size of VARCHAR fields to stick as closely as possible to the size of the data? I'm thinking of Performance: Is there an advantage to using a smaller n when selecting, filtering and sorting on the data? Memory, including on the application side (C++)? Style/validation: How important do you consider restricting colunm size to force non-sensical data imports to fail (such as 200-character surnames)? Anything else? Background: I help data integrators with the design of data flows into a database-backed system. They have to use an API that restricts their choice of data types. For character data, only VARCHAR(n) with n <= 255 is available; CHAR, NCHAR, NVARCHAR and TEXT are not. We're trying to lay down some "good practices" rules, and the question has come up if there is a real detriment to using VARCHAR(255) even for data where real maximum sizes will never exceed 30 bytes or so. Typical data volumes for one table are 1-10 Mio records with up to 150 attributes. Query performance (SELECT, with frequently extensive WHERE clauses) and application-side retrieval performance are paramount.

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for loop vs std::for_each with lambda

- by Andrey

Let's consider a template function written in C++11 which iterates over a container. Please exclude from consideration the range loop syntax because it is not yet supported by the compiler I'm working with. template <typename Container> void DoSomething(const Container& i_container) { // Option #1 for (auto it = std::begin(i_container); it != std::end(i_container); ++it) { // do something with *it } // Option #2 std::for_each(std::begin(i_container), std::end(i_container), [] (typename Container::const_reference element) { // do something with element }); } What are pros/cons of for loop vs std::for_each in terms of: a) performance? (I don't expect any difference) b) readability and maintainability? Here I see many disadvantages of for_each. It wouldn't accept a c-style array while the loop would. The declaration of the lambda formal parameter is so verbose, not possible to use auto there. It is not possible to break out of for_each. In pre- C++11 days arguments against for were a need of specifying the type for the iterator (doesn't hold any more) and an easy possibility of mistyping the loop condition (I've never done such mistake in 10 years). As a conclusion, my thoughts about for_each contradict the common opinion. What am I missing here?

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