CODE:

wchar_t *str = L"文字列";
std::string result;
char* buffer = 0;
int len = WideCharToMultiByte(CP_THREAD_ACP, 0, str, -1, buffer, 0, NULL, NULL);
	
if (len > 0){
	buffer = new char[len + 1];
	memset(buffer, 0, len + 1);
	WideCharToMultiByte(CP_THREAD_ACP, 0, str, -1, buffer, len, NULL, NULL);
	result = buffer;
	if (buffer) delete[] buffer;
}
printf("変換後:%s\n", result.c_str());