MultiByteToWideChar - @Wiki

#include <windows.h>

int main(int argc, char *argv[]) {
 
    char	pszChar[] = {"C:\\\\test\\test"};
    WCHAR*	pszWchar;
    int		nLen;
 
    // WCHAR(Unicode)に必要な文字数の取得
    nLen = MultiByteToWideChar(CP_THREAD_ACP, 0, pszChar, -1, NULL, 0);
    pszWchar = malloc(sizeof(WCHAR) * nLen);
 
    if(pszWchar)
    {
        // char- > TCHAR 変換
        nLen = MultiByteToWideChar(CP_THREAD_ACP, 0, pszChar, (int)strlen(pszChar) + 1, pszWchar, nLen);
 
        if(nLen == 0)
        {
            pszWchar = NULL;
        }
    }
 
    MessageBox(NULL, pszWchar, TEXT("WCHAR print"), MB_OK);
 
    return 1;
}