How to debug and fix a runtime error like "Unhandled exception at 0x.... in ....exe: 0xC0000005: Access violation writing location 0x...."

Question

For a project of mine, I am writing a save file reader. In the latest build I am getting a runtime error Unhandled exception at 0x00075256 in Final Assessment.exe: 0xC0000005: Access violation writing location 0xCCCCCCCC.

How can I go on to identify and correct the source of this error?

I believe the error happens when I create the ifstream object saveFile(), but I have been unable to find the exact source.

bool Game::load(){
    string data[9];
    ifstream saveFile("save.dat");
    int x = 0;
    if (saveFile.is_open()){
        while (!saveFile.eof()){
            getline(saveFile,data[x]);
            x++;
        }
        saveFile.close();

        string savePlayerName = data[0];
        int saveBaseHealth = stringToInt(data[1]);
        int saveHealth = stringToInt(data[2]);
        int saveKilled = stringToInt(data[3]);
        int saveMoney = stringToInt(data[4]);

        string saveWeaponName = data[5];;
        int saveAttack = stringToInt(data[6]);

        string saveArmorName = data[7];
        int saveDefense = stringToInt(data[8]);

        mainPlayer.setName(savePlayerName);
        mainPlayer.setBaseHealth(saveBaseHealth);
        mainPlayer.setHealth(saveHealth);
        mainPlayer.setEnemiesKilled(saveKilled);
        mainPlayer.setMoney(saveMoney);

        mainWeapon.setName(saveWeaponName);
        mainWeapon.setAttackPower(saveAttack);

        mainArmor.setName(saveArmorName);
        mainArmor.setDefense(saveDefense);
        return true;
    }
    else
    {
        return false;
    }
}

Debug

BTW, [`while (!saveFile.eof()){` is wrong](http://stackoverflow.com/q/5605125/560648). Which book told you to write that? — Lightness Races in Orbit, Oct 14 '13 at 12:03
You "believe" that's when the error happens ... when does it actually happen? What did debugging tell you? — Angew is no longer proud of SO, Oct 14 '13 at 12:05
btw redesign your while loop to `for (int x = 0; x < 9 && std::getline(saveFile, data[x]) ; ++x ) {}` — AndersK, Oct 14 '13 at 12:14

score 8 · Accepted Answer · answered Oct 14 '13 at 12:09

Maybe not the immediate reason of your crash, but here goes:

while (!saveFile.eof()) is an anti-pattern that's a common source of off-by-one errors. The reason is that it returns true only after an attempt is made to read past the end of file. That means you get one iteration too much, one x++ too much and you go out of bounds in data[x], invoking undefined behaviour.

Sometimes. Unfortunately, you might get away with it and it would appear to work.

Change the loop to

while (getline(saveFile, tempString) && x < 9) {
    data[x] = temp;
    ++x;
}

and see if it makes a difference.

(The above code doesn't account for input with less than 9 lines, mind you. Also, I'd suggest you use a std::vector instead of a C-array.)

You're right, thanks, I never realized that could cause an error. — clifford.duke, Oct 14 '13 at 12:17

How to debug and fix a runtime error like "Unhandled exception at 0x.... in ....exe: 0xC0000005: Access violation writing location 0x...."

1 Answers1