Why Does Converting a char Array to wchar_t Result in Undefined Behavior in This Code?

Convert char to wchar_t: Exploring Solutions and Resolving Function Errors

Converting a character array (char) to a wide character array (wchar_t) is a common task in UNICODE programming. While various approaches exist, we'll focus on a specific implementation that has encountered an issue.

The presented code snippet:

<code class="C++">const wchar_t *GetWC(const char *c)
{
    const size_t cSize = strlen(c)+1;
    wchar_t wc[cSize];
    mbstowcs (wc, c, cSize);
    return wc;
}</code>

is intended to perform the conversion by allocating a local wchar_t buffer, wc, of the same size as the input char string. However, this approach doesn't work as expected.

The issue stems from the fact that wc is declared as a local variable within the function. When the function call concludes, the memory allocated for wc will be deallocated, resulting in undefined behavior.

To resolve this, we must ensure that the allocated wchar_t buffer persists beyond the function's lifetime. The appropriate fix is:

<code class="C++">const wchar_t *GetWC(const char *c)
{
    const size_t cSize = strlen(c)+1;
    wchar_t* wc = new wchar_t[cSize];
    mbstowcs (wc, c, cSize);
    return wc;
}</code>

By allocating the wchar_t buffer using new, we reserve memory on the heap that won't be deallocated when the function returns. However, the responsibility for deallocating this memory now falls upon the calling code to avoid a memory leak.

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