Can someone tell me what I am doing wrong? I want to pass a NULL pointer to a function which will allocate some memory to it and assign it values. Then I want to be able to access the values outside of the function. This is probably an easy fix, but the solution is escaping me.
Code:void test(int* tmp); void main(void) { int* data = NULL; test(data); printf("%d %d\n",data[0], data[1]); } void test(int* tmp) { tmp = (int *)malloc(sizeof(int)*2); *tmp[0] = 1; *tmp[1] = 2; }
Your function receives and modifies a copy of the original pointer. You have to pass a pointer to a pointer
KurtCode:void test(int** tmp); void main(void) { int* data = NULL; test(&data); printf("%d %d\n",data[0], data[1]); } void test(int** tmp) { *tmp = malloc(sizeof(int)*2); // don't cast (*tmp)[0] = 1; // this dereferences twice (*tmp)[1] = 2; }
EDIT: don't cast the returnvalue of malloc. Look in the FAQ.
Last edited by ZuK; 04-21-2006 at 09:50 AM.
And another point: main always returns an int. Check the faq for the reason.
STL Util a small headers-only library with various utility functions. Mainly for fun but feedback is welcome.
or you can return the pointer value from the function:
Code:int* test(void); int main(void) { int* data = NULL; data = test(); printf("%d %d\n",data[0], data[1]); return 0; } int* test(void) { int *tmp = malloc(sizeof(int)*2); tmp[0] = 1; tmp[1] = 2; return tmp; }
You should free your malloc()d memory.
dwk
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Originally Posted by bithub
thankyou bithub.. this helped me a lot
