Question

Code:

void w(char* c, int i)
{
    char * t;
    sprintf(t, "%d", i);
    perror(c);
    perror(t);
}

int main(void)
{
    w("qwe", 5);
    return 0;
}

causes segmentation fault, but

int main(void)
{
    perror("qwdasda");
    w("qwe", 5);
}

works. Why?
My question does not meet your quality standards.

Answer 1

Here is your segmentation fault:

char *t;
sprintf(t,"%d",i);

In this code, t is input to sprintf(). However, t is uninitialized so sprintf() will scribble on your memory. It is almost never advisable to use sprintf(), use snprintf() instead:

char buf[32];
snprintf(buf, sizeof(buf), "%d", i);