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• Visual Studio 2010 Compiling C code

  - by Corsen2000

  I have the following code snippet. This is a c file in visual studio 2010. If i try to compile this with the line: int hello = 10; commented out it will compile just fine. If I comment that line in it will not compile. Am I missing something or should I not be using Visual Studio 2010 to compile C code. If this is a Visual Studio problem can anyone recommend a easy to use IDE / Compiler that I can for C. Thank You int* x = (int*) calloc(1, sizeof(int)); *x = 5; //int hello = 10; printf("Hello World! %i", *x); getchar();

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• Checking for an "end of line" in a C-string

  - by Numerator

  I would really love your help with the following problem: I want to get as an input from the user a maximum length of 30 chars string and check whether it contains an end of line. This is what I tried to write so far: int main(void) { int i; char* command = (char*)calloc(31, sizeof(char)); while (0 < 1) { scanf("%s", command); for (i = 0; i <= strlen(command); ++i) { if (command[i] == '\n') printf("here"); } if (strcmp(command, "quit") == 0) break; } The idea is to check whether the command given by the user as input is "legal" - that is of length < 31. when i run this code, it never prints "here" regardless of the length of input.

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• Using sizeof with a dynamically allocated array

  - by robUK

  Hello, gcc 4.4.1 c89 I have the following code snippet: #include <stdlib.h> #include <stdio.h> char *buffer = malloc(10240); /* Check for memory error */ if(!buffer) { fprintf(stderr, "Memory error\n"); return 1; } printf("sizeof(buffer) [ %d ]\n", sizeof(buffer)); However, the sizeof(buffer) always prints 4. I know that a char* is only 4 bytes. However, I have allocated the memory for 10kb. So shouldn't the size be 10240? I am wondering am I thinking right here? Many thanks for any suggestions,

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• Increase a recive buffer in UDP socket

  - by unresolved_external

  I'wm writing an app, which transmits video and obviously uses UDP protocol fot this purpose. So I am wondering how can I increase a size of send/recieve buffer, cause currently the maximal size of data, which I can send is 65000 bytes. I already tried to do it in following way: int option = 262144; if(setsockopt(m_SocketHandle,SOL_SOCKET,SO_RCVBUF ,(char*)&option,sizeof(option)) < 0) { printf("setsockopt failed\n"); } But it did not work. So how can I do it?

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• cygwin c sem_init

  - by RileyVanZeeland

  if((sem_init(sem, 1, 1)) == 1) perror("error initiating sem"); If I include this line of code my program simply starts and exits. I just started learning how to use semaphores. I'm using cygwin and when this line is commented out the printf's ABOVE this print to console but when include this, nothing happens. I did the following to get cygserver going- CYGWIN=server ran /bin/cygserver-config ran /usr/sbin/cygserver for the config it said the cygserver is already running And for the sygserver it saids- initailaizing complete failed to created named pipe: is the daemon already running? fatal error on IPC transport: closing down Any ideas?

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• Is it a header file or library? in a makefile

  - by gccinac

  I already know the differences between a header file and a library. However, when I'm writing my makefile, I have some difficulties on deciding if I should put something as a dependency of the file or just at the linking rule. For example: I have 2 simple files: main.c: #include <stdio.h> main(){ printf("this is the sine or 90"); sinus(90); } and func.c: #include <math.h> sinus(int num){ return sin(num); } and my makefile is: main: main.o func.o gcc main.o func.o -lm -o main func.o: func.c main.o: main.c Well, my question is why this makefile works and this one doesn't: main: main.o func.o gcc main.o func.o -lm -o main func.o: func.c math.h main.o: main.c

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• Why does a non-constant offsetof expression work?

  - by Chris J. Kiick

  Why does this work: #include <sys/types.h> #include <stdio.h> #include <stddef.h> typedef struct x { int a; int b[128]; } x_t; int function(int i) { size_t a; a = offsetof(x_t, b[i]); return a; } int main(int argc, char **argv) { printf("%d\n", function(atoi(argv[1]))); } If I remember the definition of offsetof correctly, it's a compile time construct. Using 'i' as the array index results in a non-constant expression. I don't understand how the compiler can evaluate the expression at compile time. Why isn't this flagged as an error?

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• Code compiles etc. but just hangs on run.

  - by Aidan

  Hey guys, My program is meant to parse through a text file, extract relevant data and then save it in a SQL table. I compile it like so.. gcc -o parse parse.c -I/usr/include/mysql -L/usr/lib/mysql -lmysqlclient_r then I run it like so... ./parse > tweets.rss But it just hangs. it doesn't print any printf's I put in to debug. Whats wrong? here is my code... http://pastebin.com/3R45zyMp I'd appreciate any help!

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• Problem with Initializing Consts

  - by UdiM

  This code, when compiled in xlC 8.0 (on AIX 6.1), produces the wrong result. It should print 12345, but instead prints 804399880. Removing the const in front of result makes the code work correctly. Where is the bug? #include <stdio.h> #include <stdlib.h> #include <string> long int foo(std::string input) { return strtol(input.c_str(), NULL, 0); } void bar() { const long int result = foo("12345"); printf("%u\n", result); } int main() { bar(); return 0; } Compilation command: /usr/vacpp/bin/xlC example.cpp -g

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• Memory allocated with malloc does not persist outside function scope?

  - by PM

  Hi, I'm a bit new to C's malloc function, but from what I know it should store the value in the heap, so you can reference it with a pointer from outside the original scope. I created a test program that is supposed to do this but I keep getting the value 0, after running the program. What am I doing wrong? int f1(int * b) { b = malloc(sizeof(int)); *b = 5; } int main() { int * a; f1(a); printf("%d\n", a); return 0; }

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• Keeping some files private

  - by user490895

  Hi, I was trying to create a directory of private files that could only be accessed when a user logs in. To do this, I used a folder outside the web directory, and then php to access it, if allowed. Here's an example: function display_movie($file){ printf("<video id='movie' width='960' height='416' controls='controls' onerror='fix()'> <source src='movie.php?file=%s' type='video/ogg; codecs=\"theora, vorbis\"'> </video>", rawurlencode($file)); } This works great for images, but breaks the media player. Also, I've only tested this locally on a Linux machine. Any ideas? Thanks.

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• Structure within union and bit field

  - by java

  #include <stdio.h> union u { struct st { int i : 4; int j : 4; int k : 4; int l; } st; int i; } u; int main() { u.i = 100; printf("%d, %d, %d", u.i, u.st.i, u.st.l); } I'm trying to figure out the output of program. The first outputs u.i = 100 but I can't understand the output for u.st.i and u.st.l. Please also explain bit fields.

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• Create a basic matrix in C (input by user !)

  - by DM

  Hi there, Im trying to ask the user to enter the number of columns and rows they want in a matrix, and then enter the values in the matrix...Im going to let them insert numbers one row at a time. How can I create such function ? #include<stdio.h> main(){ int mat[10][10],i,j; for(i=0;i<2;i++) for(j=0;j<2;j++){ scanf("%d",&mat[i][j]); } for(i=0;i<2;i++) for(j=0;j<2;j++) printf("%d",mat[i][j]); } This works for inputting the numbers, but it displays them all in one line... The issue here is that I dont know how many columns or rows the user wants, so I cant print out %d %d %d in a matrix form .. Any thoughts ? Thanks :)

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• pointers for getting elements of an array in C

  - by Manolo

  I am a newbie in C and I would like to get the elements of an array with a function, I have tried different options, but I still do not get the elements. My function is: void getelements(int *a, int cl) { int *p; for (p=&a[0];p<&a[cl];p++) { printf("%d\n",*p); } } I know that the solution should work like that, but it only prints the first element and then memory positions. I am calling my function with: int v={10,12,20,34,45}; getelements(&v,5); Any help? I need to use arithmetic of pointers. Thanks

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• Difficulty understanding behavior of free()

  - by Rasmi Ranjan Nayak

  int main() { int *ptr, **ptr1; ptr = (int*)malloc(sizeof(int)); ptr1 = (int**)malloc(sizeof(int)); free(ptr); *ptr = 12345; ptr1 = &ptr; //free(ptr); //**ptr1 = 23456; printf("%d \n", **ptr1); system("pause"); return 0; } How does *ptr store the value 12345, when the memory has already been freed? So, now ptr should be pointing to garbage. Why is this happening?

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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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• C++ operator[] syntax.

  - by Lanissum

  Just a quick syntax question. I'm writing a map class (for school). If I define the following operator overload: template<typename Key, typename Val> class Map {... Val* operator[](Key k); What happens when a user writes: Map<int,int> myMap; map[10] = 3; Doing something like that will only overwrite a temporary copy of the [null] pointer at Key k. Is it even possible to do: map[10] = 3; printf("%i\n", map[10]); with the same operator overload?

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• Enter custom file name to be read ?

  - by ZaZu

  Hello, I want to allow users to type the name of any .txt file to be read/written. This is my code : printf("Enter .txt file name\n"); scanf("%s",&fname); FILE *inputf; inputf=fopen(&fname,"w"); Problem is this method does not work (having &fname) as a parameter. I can imagine its because C needs "filename.txt" for it work ... even if I enter for example : "custom.txt", the program returns an error of "Storage block not big enough for this operation" What is the correct method to accomplish this ? Im using C and im pretty much using basic commands .. (not too advanced) Thanks alot !!!

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• Same memory space being allocated again & again

  - by shadyabhi

  In each loop iteration, variable j is declared again and again. Then why is its address remaining same? Shouldn't it be given some random address each time? Is this compiler dependent? #include<stdio.h> #include<malloc.h> int main() { int i=3; while (i--) { int j; printf("%p\n", &j); } return 0; } Testrun:- shadyabhi@shadyabhi-desktop:~/c$ gcc test.c shadyabhi@shadyabhi-desktop:~/c$ ./a.out 0x7fffc0b8e138 0x7fffc0b8e138 0x7fffc0b8e138 shadyabhi@shadyabhi-desktop:~/c$

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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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• Same memory space being allocated again & again while using malloc()

  - by shadyabhi

  In each loop iteration, variable j is declared again and again. Then why is its address remaining same? Shouldn't it be given some random address each time? Is this compiler dependent? #include<stdio.h> #include<malloc.h> int main() { int i=3; while (i--) { int j; printf("%p\n", &j); } return 0; } Testrun:- shadyabhi@shadyabhi-desktop:~/c$ gcc test.c shadyabhi@shadyabhi-desktop:~/c$ ./a.out 0x7fffc0b8e138 0x7fffc0b8e138 0x7fffc0b8e138 shadyabhi@shadyabhi-desktop:~/c$

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• Getting MATLAB variable (string) from C

  - by Hamming

  Hi! I'm writing a small C application that launchs a Matlab script (.m file). I need to exchange some variables and I don't know how to get an array of chars that exists in Matlab. I'm doing something like this: enter code here result = engGetVariable(ep,"X"); if (!result) { printf ("Error..."); exit -1; } int n = mxGetN(result); char *varx = NULL; memcpy(varx, mxGetData(result),n*sizeof(char)); It doesn't work. Does someone know how to get a Matlab string in C? I've read Matlab documentation about engGetVariable() and the provided example but any of this things clarify me.

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• CUDA error message : unspecified launch failure

  - by user1297065

  I received the error message "unspecified launch failure" in following part. off_t *matches_position; ...... cudaMalloc ( (void **) &mat_position, sizeof(off_t)*10); ...... cudaMemcpy (mat_position, matches_position, sizeof(off_t)*10, cudaMemcpyHostToDevice ); ...... err=cudaMemcpy (matches_position, mat_position, sizeof(off_t)*10, cudaMemcpyDeviceToHost ); if(err!=cudaSuccess) { printf("\n3 %s\n", cudaGetErrorString(err)); } Do you know why this error message is reported??

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• How do I make child thread exit when main thread exit?

  - by httpinterpret

  void forloop2() { int i = 0; while(TRUE) { printf("forloop2\n"); } } int main() { GThread *Thread1; GtkWidget *window; g_thread_init(NULL); gdk_threads_init(); gdk_threads_enter (); Thread1 = g_thread_create((GThreadFunc)forloop2, NULL, TRUE, NULL); gtk_init(NULL, NULL); window = gtk_window_new(GTK_WINDOW_TOPLEVEL); gtk_widget_show_all (window); gtk_main(); g_thread_join(Thread1); gdk_threads_leave (); } When I close the window, how to make Thread1 also exit?

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• define macro in C wont work

  - by Spidfire

  Im trying to make a macro in C that can tell if a char is a hex number ( 0-9 a-z A-Z) #define _hex(x) (((x) >= "0" && (x) <= "9" )||( (x) >= "a" && (x) <= "z") || ((x) >= "A" && (x) <= "Z") ? "true" : "false") this what ive come up with but it wont work with a loop like this char a; for(a = "a" ; a < "z";a++){ printf("%s => %s",a, _hex(a)); } but it gives a error test.c:8: warning: assignment makes integer from pointer without a cast test.c:8: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer

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