memcmp strangely fails returning array

Question

I have C++ code that looks like this:

static int* ArrayGenerator()
{
    int temp[1] = {9};
    return temp;
}

static int* ArrayGenerator(int i)
{
    //parameter is just for demonstration
    int temp[1] = {9};
    return temp;
}

int _tmain(int argc, _TCHAR* argv[])
{
    int arr1[1] = {9};
    printf("arrays are %s equal\n\n", (memcmp(arr1, ArrayGenerator(), 1) == 0) ? "" : "not");
    printf("arrays are %s equal\n\n", (memcmp(arr1, ArrayGenerator(1), 1) == 0) ? "" : "not");
}

The first gives me 'are equal' the second gives me 'are not equal'.

Why is this?

You should consider yourself lucky you didn't open a wormhole or something. — cHao, Jan 07 '14 at 17:16
Turn on compiler diagnostics. You return a pointer to a stack variable, you shouldn't do that. — erenon, Jan 07 '14 at 17:17
Did you, by any chance, mix up `static` functions with `static` local variables? — jrok, Jan 07 '14 at 17:19
not sure why the downvotes. it may be a stupid thing to do, but it's not a stupid question — happygilmore, Jan 08 '14 at 00:34

score 0 · Answer 1 · edited May 23 '17 at 12:19

0

You cannot return local pointers from a function. When you return temp from the functions it passes out of scope and the memory is no longer valid. This causes undefined behavior. I already explained this here

edited May 23 '17 at 12:19

Community

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answered Jan 07 '14 at 17:19

ApproachingDarknessFish

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memcmp strangely fails returning array

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