Heap corruption while trying to free a wchar_t pointer

Question

This is a code that evaluates if a wide string is either L"false" or L"true", but when I try to run it, it gives me this error when trying to free the duplicate string pointer "HEAP CORRUPTION DETECTED: after Normal block(#135756) at 0x00000000002EB3A0. CRT detected that the application wrote to memory after end of heap buffer.".

Here is the inline code:

const wchar_t* sequence = L"false";

wchar_t* duplicate;
size_t length = wcslen(sequence) + 1;

duplicate = static_cast<wchar_t*>(malloc(length));

wcscpy_s(duplicate, length, sequence);

int boolean = -1;

if (wcscmp(duplicate, L"false") == 0) {
    boolean = 0;
}
else if (wcscmp(duplicate, L"true") == 0) {
    boolean = 1;
}

free(duplicate);

All the string pointers seem to be OK right before the free statement. I am sure I have done some serious mistake simply because I was able to corrupt the heap.

Compiler: Microsoft Visual Studio 2015 RC

Processor: Inter Core i5-3450 3.10 GHz

Answer 1

Use

duplicate = static_cast(malloc(length * sizeof(wchar_t));

otherwise you do not hane enough space for the wide string