local variables in C

Question

when I try the following code in visual studio it gives me 45 but when I run it in online compilers some give me an error and some give me 0.I was expecting that they all give me an error.how is that they are not?! thanks

#include <stdio.h>

int *f(int *a)
{
    *a = 23;
    int b = 45;
    return &b;
}

int main(void)
{
    int i = 2;
    int *p;
    p = f(&i);

    printf("The return value of function f: %d\n\n", *p);
    return 0;
}

You are returning a reference to a stack allocated variable - this is **very** bad!! Don't do this, this can cause tons of nasty, hidden bugs — UnholySheep, Oct 21 '16 at 17:50
Even if you are getting correct value in visual studio, this is wrong. You don't get any error since function's return type is int* and you are returning an int*. — MayurK, Oct 21 '16 at 17:51

Ed Heal · Answer 1 · 2016-10-21T17:52:48.907

1

Problem:

return &b;

You are returning a pointer to a local variable that is going out of scope - hence the pointer will be invalid

If you get an error depends on the various settings for that compiler

edited Oct 21 '16 at 17:52

answered Oct 21 '16 at 17:50

Ed Heal

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I guess that's why she expected the compilers to give an error. So it does not answer the question. – Frank Puffer Oct 21 '16 at 17:51
The compiler doesn't give an error, as there is no error in this specific line and it is perfectly legal... – Eugene Sh. Oct 21 '16 at 17:53
@EugeneSh.- Just because you do not get caught does not mean that it is legal. The thief on that occasion was lucky – Ed Heal Oct 21 '16 at 17:55
1

@EdHeal Returning an address of a local variable is perfectly legal. Dereferencing it is UB. – Eugene Sh. Oct 21 '16 at 17:56

local variables in C

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