hello everybody,
I have written a simple program with malloc ,and I am getting segmentation fault . Can anyone tell me why its so?
Thanks in advance
Code:#include<stdio.h> #include<malloc.h> int main() { int **a; a[0]=(int *)malloc(2*(sizeof(int))); }
You're accessing memory your program does not own.Originally Posted by BharathKumar
1) <malloc.h> is a nonstandard header. When using malloc(), you should #include <stdlib.h> instead.
2) You don't have to cast malloc() - see
http://faq.cprogramming.com/cgi-bin/...&id=1043284351
3) You need to allocate space for a[0], a[1], etc. BEFORE using malloc() to assign memory to each of them. For example, if you wanted to allocate space for a[0], a[1], and a[2], you could write
4) Of course you should check for NULL after calling each malloc() - I neglected to do this in the example above.Code:int **a; a = malloc(3*sizeof(int *)); /* allocates space for a[0], a[1], a[2] */ a[0] = malloc(2*sizeof(int)); /* allocates space for a[0][0], a[0][1] */
Thank You Robatino .
And you should free the memory you've allocated, once your done with it
Eg:
Code:#include <stdlib.h> int main(void) { const size_t rows = 3, cols = 5; int ** a; size_t c; /* allocate rows */ if((a = malloc(rows * sizeof(int *))) == NULL) { perror("Failed to allocate rows"); return 1; } /* allocate cols */ for(c = 0; c < rows; c++) { if((a[c] = malloc(cols * sizeof(int))) == NULL) { perror("Failed to allocate cols"); return 2; /* ideally you should free the cols and rows, but cbf :) */ } } /* do whatever with rows and cols */ /* free cols */ for(c = 0; c < rows; c++) { free(a[c]); a[c] = NULL; } /* free rows */ free(a); a = NULL; return 0; }
Last edited by zacs7; 06-26-2007 at 05:25 AM.
Thank You Zacs7 ,as I had missed that part.
