allocate memory in subfunctions?

[claphahat]

i don't understand the difference here:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char *blah;

void getmem()
{
      blah = malloc(10);
}

int main()
{
      char buffer[10];

      getmem();
      fgets(buffer, sizeof buffer, stdin);
      strcpy(blah, buffer);
      puts(blah);
      return 0;
}

in the above case the memory is apparently allocated inside getmem, then disappears once getmem returns, but in the below case...

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct ex {
      char *ptr_1;
} whatever;

void getmem(struct ex *ptr)
{
      ptr->ptr_1 = malloc(10);
}

int main()
{
      struct ex *ptr_whatever;
      char buffer[10];

      ptr_whatever = &whatever;
      getmem(ptr_whatever);
      fgets(buffer, sizeof buffer, stdin);
      strcpy(ptr_whatever->ptr_1, buffer);
      puts(ptr_whatever->ptr_1);
      return 0;
}

...the only difference i can see is that the pointer is stored within a structure but its memory is allocated so that it can still be used by main. in the first case strcpy causes a seg fault and in the second case everything works perfectly. why is this so?

[jimblumberg]

in the above case the memory is apparently allocated inside getmem, then disappears once getmem returns, but in the below case...

Since blah is a global variable, the memory does not go out of scope when the function returns. The first program works for me.


Jim