Function returning a structure and function returning a string-- Different behaviour?

Hi,

I have heard that we cannot return a pointer to a local (automatic) array variable from a function since the automatic variable have limited scope and they die off once the called function returns.

Code:

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char *s getName()
{
char name[]="Sumit";  // Automatic variable
retrun name; // No scope outside the function

}

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But a doubt arises in my mind:

Code:

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struct info getInfo(int a,int b)
{

struct info f1; // Automatic variable memory allocated for a structure
f1.a=a;
f1.b=b;

return f1;

}

---

here also we are returning a reference to a memory location which is allocated locally. Then how come here it works perfectly fine.


PLZ HELP
Waiting for reply

You are not returning a reference to a memory location, so the analogy fails. (If you were returning &f1, then you would be in the same world of hurt that you were in before.)

As tabstop points out ... C cannot return arrays. It can return a struct, because it knows how big it is. (Well, actually it's returning a copy of a struct) Of course it can return a string in a struct...

Here's an example to demonstrate why you should never try to retun arrays from functions in C...

Code:

---

#include <stdio.h>

int* MyFunction(int a, int b, int c)
  {  static int array[3];
    array[0] = a;
    array[1] = b;
    array[2] = c;
    return array;  } // return a pointer.


int main (void)
  { int *a1, *a2;  // int pointers

    printf("calling a1 = MyFunction(10,20,30);\t");
    a1 = MyFunction(10,20,30);
    printf("a1 has %d %d %d\n",a1[0],a1[1],a1[2]);

    printf("calling a2 = MyFunction(100,200,300);\t");
    a2 = MyFunction(100,200,300);
    printf("a2 has %d %d %d\n",a2[0],a2[1],a2[2]);

    printf("\nLooks good, except...\t");
    printf("a1 now has %d %d %d\n",a1[0],a1[1],a1[2]);

    getchar();
    return 0; }

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Try it both with and without the static keyword...

@tabstop: Thnnx for ur reply.
But another doubt here:
Why cant we return a pointer to that memory allocated although we are able to return the memory chunk itself?

The memory allocated in both cases (in case of an array and in case of a structure) are local to the function.
The how come it is getting retained in structure case and gets destroyed in case of an array?

Quote:

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Originally Posted by tabstop

You are not returning a reference to a memory location, so the analogy fails. (If you were returning &f1, then you would be in the same world of hurt that you were in before.)

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Just as a copy of int a and int b are made going in to your function, a copy of the struct (or whatever is returned) is made coming out. (If you return a pointer, the pointer is copied, but that doesn't help because the address it points to is no longer valid.)

Quote:

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Originally Posted by tabstop

Just as a copy of int a and int b are made going in to your function, a copy of the struct (or whatever is returned) is made coming out. (If you return a pointer, the pointer is copied, but that doesn't help because the address it points to is no longer valid.)

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Thank you very much for clearing the the things... :)