#define 
//only for posix here, for win it is similar
PROTECT_END_FUNC(RETURN) \
	RETURN; \
	__end: \
	asm volatile ( \
		"\t.ascii \""PROTECT_END_MARKER"\"\n" \
	)
//and calling it like this (stupid example):
int testfn1(void){
	int j=0;
	PROTECT_START_FUNC(Decrypt);
	PromptOK("testfn1 DECRYPTED SUCCESSFULLY!!!");
	return j; // <- returning in between wouldn't hurt 
	PROTECT_END_FUNC(return j);
}

if(!__decrypted)
    goto __end;

bool TestLicense(){
    bool b;
    try{
        PROTECT_START_FUNC(decrFunc);
        b=true;
        PROTECT_END_FUNC;
    }catch (...) {
        Exclamation("Invalid license, get a new one!");
        b=false;
    }
    return b;
}

main()
{
    String guard = "someencryptedtextofwhichyouknowthedecryptresult";
    String key = GetGey();
    Buffer<byte>buf(guard.GetCount());
    memcpy(buf, ~guard, guard.GetCount());
    RC4 rc4(key);
    rc4.Crypt(buf, buf, guard.GetCount());
    if(strncmp(buf, "yourknowndecryptedtext", guard.GetCount())
    {
        PromptOK("Invalid license key!!!");
        exit(1);
    }

    // here rest of your app

}

ON_PROTECT_BAD_KEY(Decrypt)
{
    PromptOK("Bad License !!!");
    exit(1);
}