assert.c

#include <string.h>
#include <assert.h>
#include <windows.h>

#define FORMAT "%s:%d: Assertion `%s' failed."

void _assert(const char *msg, const char *file, int line) {
	size_t len = strlen(msg) + strlen(file) + sizeof FORMAT + 2 + 8 - 6;
	char text[len];
	wchar_t wtext[len];
	sprintf(text, FORMAT, file, line, msg);
	fputs(text, stderr);
	fputc('\n', stderr);
	mbstowcs(wtext, text, len);
	OutputDebugStringW(wtext);
	MessageBoxW(NULL, wtext, L"Assertion failed", 0);
	abort();
}