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• format specifier for short integer

  - by cateof

  I don't use correctly the format specifiers in C. A few lines of code: int main() { char dest[]="stack"; unsigned short val = 500; char c = 'a'; char* final = (char*) malloc(strlen(dest) + 6); snprintf(final, strlen(dest)+6, "%c%c%hd%c%c%s", c, c, val, c, c, dest); printf("%s\n", final); return 0; } I want my executable to print aa500aastack and not aa500aasta Why I am loosing 2 byte? What is the correct format specifier for an unsighed short integer? thanks.

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• External class-calling

  - by anonymous

  Hi guys i have a bit of a problem with a few classes, and i would be very grateful if someone can help me out. So i have: Already compiled executable (for whom i don't have the source) A class in that program that i want to call The program doesn't have export for the class, and that's my problem i don't have definition for this class, so is there a way to get a callback to this class? Example: In the compiled executable: foo::bar (example) { printf(example); } My app: CALLBACK(foo::bar, "this text must be passed as argument") Or in other words i want to call a class in other executable (without having its source) and pass arguments to its function.

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• How Do I See The Final Text Of A Query Resulting From A Call To mysqli->prepare?

  - by Joshua

  After code like this: $stmt = $mysqli->prepare("SELECT District FROM City WHERE Name=?")) { $stmt->bind_param("s", $city); $stmt->execute(); $stmt->bind_result($district); $stmt->fetch(); printf("%s is in district %s\n", $city, $district); How Do I See The Actual SQL Statement That Was Executed? (It Should Look Something Like "SELECT District FROM City WHERE Name='Simi Valley';") I already realize that in this simplistic case it would be very easy to simply reconstruct the query... but how can I access it in a general way that will work for very complicated prepared statements, and cases where I don't necessarily already understand the intended structure of the query, etc. Isn't there some function or method that can be called on the statement object that will return the actual text of the SQL query, after binding?

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• Ignore carriage returns in scanf before data.... to keep layout of console based graphics with conio

  - by volting

  I have the misfortune of having use conio.h in vc++ 6 for a college assignment, My problem is that my graphic setup is in the center of the screen... e.g. gotoxy( getcols()/2, getrows()/2); printf("Enter something"); scanf( "%d", &something ); now if someone accidentally hits enter before they enter the "something", then the cursor gets reset to the left of the screen on the next line. Iv tried flushing the keyboard and bios buffers with fflush(stdin) and getchar(), which like I expected didn't work! Any help/ideas would be appreciated, Thanks, V

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• How to invoke an Objective-C Block via the LLVM C++ API?

  - by smokris

  Say, for example, I have an Objective-C compiled Module that contains something like the following: typedef bool (^BoolBlock)(void); BoolBlock returnABlock(void) { return Block_copy(^bool(void){ printf("Block executing.\n"); return YES; }); } ...then, using the LLVM C++ API, I load that Module and create a CallInst to call the returnABlock() function: Function *returnABlockFunction = returnABlockModule->getFunction(std::string("returnABlock")); CallInst *returnABlockCall = CallInst::Create(returnABlockFunction, "returnABlockCall", entryBlock); How can I then invoke the Block returned via the returnABlockCall object?

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• what does this code do?

  - by bstullkid

  It looks like this just sends a ping, but whats the point of that when you can just use ping? int main (int argc, char *argv[]) { unsigned int pid = 0; char buffer[2]; char *args[] = { "/bin/ping", "-c", "5", NULL, NULL }; if (argc != 2) return 0; args[3] = strdup(argv[1]); for (;;) { gets(buffer); /* FTW */ if (buffer[0] == 0x6e) break; switch (pid = fork()) { case -1: printf("Error Forking\n"); exit(255); case 0: execvp(args[0], args); exit(1); default: break; } } return 255; }

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• What is the safest way to pass strings around in C?

  - by chucknelson

  I have a program in C using Solaris with VERY ancient compatibility it seems. Many examples, even here on SO, don't work, as well as lots of code I've written on Mac OS X. So when using very strict C, what is the safest way to pass strings? I'm currently using char pointers all over the place, due to what I thought was simplicity. So I have functions that return char*, I'm passing char* to them, etc. I'm already seeing strange behavior, like a char* I passed having its value right when I enter a function, and then the value being mysteriously gone OR corrupted/overwritten after something simple like one printf() or an malloc to some other pointer. I was thinking maybe declaring a local char[] inside each function, using strcpy() immediately, and then eventually returning a pointer where char *returnval = strdup(localchar[]); This seems...sloppy. Can anyone point me in the right direction on a simple requirement?

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• doubt in sizeof implementation

  - by aks

  Below is the program to find the size of a structure without using sizeof operator: struct MyStruct { int i; int j; }; int main() { struct MyStruct *p=0; int size = ((char*)(p+1))-((char*)p); printf("\nSIZE : [%d]\nSIZE : [%d]\n", size); return 0; } My doubt is: Why is typecasting to char * required? If I don't use the char* pointer, the output is 1 - WHY?

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• How to recive more than 65000 bytes in C++ socket using recv()

  - by Mr.Cool

  I am developing a client server application (TCP) in Linux using C++. I want to send more than 65,000 bytes at the same time. In TCP, the maximum packet size is 65,635 bytes only. How can I send the entire bytes without loss? Following is my code at server side. //Receive the message from client socket if((iByteCount = recv(GetSocketId(), buffer, MAXRECV, MSG_WAITALL)) > 0) { printf("\n Received bytes %d\n", iByteCount); SetReceivedMessage(buffer); return LS_RESULT_OK; } If I use MSG_WAITALL it takes a long time to receive the bytes so how can I set the flag to receive more than 10 lakhs bytes at time.

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• How does dereferencing of a function pointer happen?

  - by eSKay

  Why and how does dereferencing a function pointer just "do nothing"? This is what I am talking about: #include<stdio.h> void hello() { printf("hello"); } int main(void) { (*****hello)(); } From a comment over here: function pointers dereference just fine, but the resulting function designator will be immediately converted back to a function pointer And from an answer here: Dereferencing (in way you think) a function's pointer means: accessing a CODE memory as it would be a DATA memory. Function pointer isn't suppose to be dereferenced in that way. Instead, it is called. I would use a name "dereference" side by side with "call". It's OK. Anyway: C is designed in such a way that both function name identifier as well as variable holding function's pointer mean the same: address to CODE memory. And it allows to jump to that memory by using call () syntax either on an identifier or variable. How exactly does dereferencing of a function pointer work?

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• Glib convert epoch time to string.

  - by PP

  I am using glibs functions to convert epoch time to string as follows. But each time it is giving me some random time. //Convert Time in string. GDate *date = g_date_new_julian(timestampsecs); gchar date_string[50]; g_date_strftime(date_string, 50, (const gchar*)"%a, %I:%M %p", (const GDate*)date); printf("Date String [%s]\n", date_string ); Why this might be happening? am i missing anything? Thanks, PP.

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• Linux issues on setting a timer function

  - by laura

  I am creating a process with 2 children, 1 of the children is responsible to read questions (line by line from a file), output every question and reading the answer, and the other one is responsable to measure the time elapsed and notify the user at each past 1 minute about the remaining time. My problem is that i couldn't find any useful example of how i can make this set time function to work. Here is what i have tried so far. The problem is that it outputs the same elapsed time every time and never gets out from the loop. #include<time.h> #define T 600000 int main(){ clock_t start, end; double elapsed; start = clock(); end = start + T; while(clock() < end){ elapsed = (double) (end - clock()) / CLOCKS_PER_SEC; printf("you have %f seconds left\n", elapsed); sleep(60); } return 0; }

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• Fastest way to zero out a 2d array in C?

  - by Eddy

  I want to repeatedly zero a large 2d array in C. This is what I do at the moment: for(j = 0; j < n; j++) { for(i = 0; i < n; i++) { array[i][j] = 0; } } I've tried using memset: memset(array, 0, sizeof(array)) But this only works for 1D arrays. When I printf the contents of the 2D array, the first row is zeroes, but then I got a load of random large numbers and it crashes.

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• g_tree_insert overwrites all data

  - by pechenie

  I wonder how I should use the GTree (from GLib) to store data? Every new value I insert into GTree with g_tree_insert routine is overwrite the previous one! GTree *tree; //init tree = g_tree_new( g_str_equal ); //"g_str_equal" is a GLib default compare func //... for( i = 0; i < 100; ++i ) g_tree_insert( tree, random_key(), random_value() ); //insert some random vals // printf( "%d", g_tree_nnodes( tree ) ); //should be 100? NO! Prints "1"!!! What am I doing wrong? Thank you.

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• How to access a structure member in a function that get it as void* type?

  - by Ahmad

  I want to have a function that accepts different type of structures as argument. So, since I don't have a specific type, I have to use void*. Now question is: when I pass a structure to this function, how can I access a known member of this structure inside the function? Specifically, I know that all structures have str1 as a member and I want, for example, print it. Here is a sample code: struct { char* str1; float tt1; } var1 = {"This is me", 12}; struct { char* str1; int tt2; } var2 = {"This is you", 18}; void printStruct(void* str) { printf("\n the structure string is %s", ??); //can I put something in ?? to print the string? } main(....) { printStruct(&var1); printStruct(&var2); }

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• Why does this give a segmentation fault?

  - by nightcracker

  I'm stunned, why does this code give me a segmentation fault? #include <stdio.h> #define LIMIT 1500000 typedef struct { int p; int a; int b; } triplet; int main(int argc, char **argv) { int i; triplet triplets[LIMIT]; for (i = 0; i < 5; i++) { triplets[i].p = 9; // remove this line and everything works fine } printf("%d\n", triplets[15].p); return 0; } EDIT: After changing LIMIT to 150 I no longer get a segmentation fault, it prints random numbers instead.

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• Odd C interview question

  - by Brennan Vincent

  Hi guys. I found this problem on a site full of interview questions, and was stumped by it. Is there some preprocessor directive that allows one to read from standard input during compilation? Write a small C program, which while compiling takes another program from input terminal, and on running gives the result for the second program. (NOTE: The key is, think UNIX). Suppose, the program is 1.c Then, while compiling $ cc -o 1 1.c int main() { printf("Hello World\n"); } ^D $ ./1 Hello World

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• Should I use implicit conversions to enforce preconditions?

  - by Malvolio

  It occurs to me that I could use use implicit conversions to both announce and enforce preconditions. Consider this: object NonNegativeDouble { implicit def int2nnd(d : Double) : NonNegativeDouble = new NonNegativeDouble(d) implicit def nnd2int(d : NonNegativeDouble) : Double = d.v def sqrt(n : NonNegativeDouble) : NonNegativeDouble = scala.math.sqrt(n) } class NonNegativeDouble(val v : Double ) { if (v < 0) { throw new IllegalArgumentException("negative value") } } object Test { def t1 = { val d : Double = NonNegativeDouble.sqrt(3.0); printf("%f\n", d); val n : Double = NonNegativeDouble.sqrt(-3.0); } } Ignore for the moment the actual vacuity of the example: my point is, the subclass NonNegativeDouble expresses the notion that a function only takes a subset of the entire range of the class's values. First is this: A good idea, a bad idea, or an obvious idea everybody else already knows about Second, this would be most useful with basic types, like Int and String. Those classes are final, of course, so is there a good way to not only use the restricted type in functions (that's what the second implicit is for) but also delegate to all methods on the underlying value (short of hand-implementing every delegation)?

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• How do I compile for windows XP under windows 7 / visual studio 2008

  - by Jon Cage

  I'm running Windows 7 and Visual Studio 2008 Pro and trying to get my application to work on Windows XP SP3. It's a really minimal command line program so should have any ridiculous dependencies: // XPBuild.cpp : Defines the entry point for the console application. // #include "stdafx.h" int _tmain(int argc, _TCHAR* argv[]) { printf("Hello world"); getchar(); return 0; } I read somewhere that defining several constants such as WINVER should allow me to compile for other platforms. I've tried the added the following to my /D compiler options: ;WINVER=0x0501;_WIN32_WINNT 0x0501;NTDDI_VERSION=NTDDI_WINXP But that made no difference. When I run it on my Windows XP machine (actually running in a virtualbox) I get the following error: This application has failed to start because the application configuration is incorrect. Reinstalling the application may fix this problem. So what have I missed? Is there something else required to run MSVC compiled programs or a different compiler option or something else?

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• Whats the problem with int *p=23;

  - by piemesons

  Yesterday in my interview I was asked this question. (At that time I was highly pressurized by so many abrupt questions). int *p; *p=23; printf('%d',*p); Is there any problem with this code? I explained him that you are trying to assign value to a pointer to whom memory is not allocated. But the way he reacted, it was like I am wrong. Although I got the job but after that he said Mohit think about this question again. I don't know what he was trying to say. Please let me know is there any problem in my answer?

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• Quick strlen question

  - by LearningC

  Hi again. I've come to bother you all with another probably really simple C question. Using the following code: int get_len(char *string){ printf("len: %lu\n", strlen(string)); return 0; } int main(){ char *x = "test"; char y[4] = {'t','e','s','t'}; get_len(x); // len: 4 get_len(y); // len: 6 return 0; } 2 questions. Why are they different and why is y 6? Thanks guys.

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• Interrupt On GAS

  - by Nathan Campos

  I'm trying to convert my simple program from Intel syntax to the AT&T(to compile it with GAS). I've successfully converted a big part of my application, but I'm still getting an error with the int(the interrupts). My function is like this: printf: mov $0x0e, %ah mov $0x07, %bl nextchar: lodsb or %al, %al jz return int 10 jmp nextchar return: ret msg db "Welcome To Track!", 0Ah But when I compile it, I got this: hello.S: Assembler messages: hello.S:13: Error: operand size mismatch for int' hello.S:19: Error: no such instruction:msg db "Hello, World!",0Ah' What I need to do?

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• Generating random numbers in C

  - by moonstruckhorrors

  While searching for Tutorials on generating random numbers in C I found This Topic When I try to use the rand() function with parameters, I always get the random number generated 0. When I try to use the rand() function with parameters, I always get the value 41. And whenever I try to use arc4random() and random() functions, I get a LNK2019 error. Here's what I'm doing: #include <stdlib.h> int main() { int x; x = rand(6); printf("%d", x); } This code always generate 41. Where am I going wrong?? P.S. : I'm running Windows XP SP3 and using VS2010 Command Prompt as compiler. P.P.S. : Took me 15 minutes to learn how to format properly.

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• Force line-buffering of stdout when piping to tee

  - by houbysoft

  Usually, stdout is line-buffered. In other words, as long as your printf argument ends with a newline, you can expect the line to be printed instantly. This does not appear to hold when using a pipe to redirect to tee. I have a C++ program, a, that outputs strings, always \n-terminated, to stdout. When it is run by itself (./a), everything prints correctly and at the right time, as expected. However, if I pipe it to tee (./a | tee output.txt), it doesn't print anything until it quits, which defeats the purpose of using tee. I know that I could fix it by adding a fflush(stdout) after each printing operation in the C++ program. But is there a cleaner, easier way? Is there a command I can run, for example, that would force stdout to be line-buffered, even when using a pipe?

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• What is wrong with the program

  - by Naveen

  I am getting error for below code: #include "parent_child.h" #include "child_proces.h" int main() { childprocess::childprocess(){} childprocess::~childprocess(){} /* parentchild *cp = NULL; act.sa_sigaction = cp->SignalHandlerCallback; act.sa_flags = SA_SIGINFO; sigaction(SIGKILL, &act, NULL); }*/ printf("Child process\n"); return 0; } ERROR: child_proces.cpp: In function âint main()â: child_proces.cpp:11: error: expected ;' before â{â token child_proces.cpp:12: error: no matching function for call to âchildprocess::~childprocess()â child_proces.h:9: note: candidates are: childprocess::~childprocess() child_proces.cpp:12: error: expected;' before â{â token

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