Double indirection and structures passed into a function

Posted by ZPS on Stack Overflow See other posts from Stack Overflow or by ZPS
Published on 2010-03-30T21:14:36Z Indexed on 2010/03/30 21:23 UTC
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I am curious why this code works:

typedef struct test_struct {
  int id;
} test_struct;

void test_func(test_struct ** my_struct)
{
test_struct my_test_struct;
my_test_struct.id=267;

*my_struct = &my_test_struct;
}

int main ()
{
test_struct * main_struct;
test_func(&main_struct);    
printf("%d\n",main_struct->id);
}

This works, but pointing to the memory address of a functions local variable is a big no-no, right?

But if i used a structure pointer and malloc, that would be the correct way, right?

void test_func(test_struct ** my_struct)
{
test_struct *my_test_struct;
my_test_struct = malloc(sizeof(test_struct));
my_test_struct->id=267;

*my_struct = my_test_struct;
}

int main ()
{
test_struct * main_struct;
test_func(&main_struct);    
printf("%d\n",main_struct->id);
}

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