Why do I get a Run-Time Check Failure #2

Question

Im new to C Programming and the Windows API im getting "Run-Time Check Failure #2 - Stack around the variable 'pMyStringAdress' was corrupted." after compilation in Visual Studio

Thats my code:

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

char MyStrings[] = "ich bin ein text";

int main() {    
    SIZE_T SizeMyStrings = sizeof(MyStrings);

    PVOID pMyStringAdress = VirtualAlloc(
        NULL,
        SizeMyStrings,
        MEM_COMMIT | MEM_RESERVE,
        PAGE_READWRITE
    );

    if (pMyStringAdress == NULL) {
        printf("VirtualAlloc fehlgeschlagen mit fehlercode %d", GetLastError());
    }
    else {
        printf("Speicher erfolgreich allokiert sitzt bei: %p\n", &pMyStringAdress);
    }

    printf("Probiere in den Speicher zu schreiben.");
    memcpy(&pMyStringAdress, MyStrings, SizeMyStrings);
    return 0;
}

Jabberwocky · Accepted Answer · 2025-11-12 10:13:36Z

6

You're copying into the wrong address.

pMyStringAdress is a pointer that holds the heap address returned by VirtualAlloc.

But you used &pMyStringAdress (the address of the pointer variable on the stack) both when printing and in memcpy. That writes past the pointer variable itself and trashes the stack, hence the message "Run-Time Check Failure #2 … stack … was corrupted."

Fixes

Use pMyStringAdress (no &) when printing and copying.
Free with VirtualFree when done.
Minor: use the right printf specifiers.

edited Nov 12 at 10:13

Jabberwocky

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answered Nov 12 at 9:49

muraya

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1 Comment

Lundin · Accepted Answer · 2025-11-12 09:17:41Z

3

This is because of Windows' dysfunctional type system. PVOID is similar to void* and so when you do memcpy(&pMyStringAdress you get a void** which is wrong. Drop the & during memcpy.

answered Nov 12 at 9:17

Lundin

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1 Comment

muraya Nov 13 at 17:53

This answer is short but this reply contains a very clear answer. Good!

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