only on DEBUG this code crashes

For Beginners

Started by EvilNando July 17, 2011 09:54 AM

12 comments, last by EvilNando 12 years, 9 months ago

Author

July 17, 2011 09:54 AM



int main()

{

    ifstream _file_input("GameData.dat", ios::binary);

    for (int _idx = 0; _idx < 3; _idx++)

    {        

        //cout<<"size of Monster "<<sizeof(GameMonster)<<" ";

        //cout<<"current seek pointer position :"<<_file_input.tellg()<<endl;



        //_file_input.seekg(_idx * sizeof(GameMonster));

        _file_input.read((char*)&_monster, sizeof(GameMonster));



        cout<<_monster.Damage<<" "<<_monster.Hp<<" "<<_monster.Name<<endl;        

    }  



    _file_input.close();



    cout<<"\nPress a key"<<endl;

    getchar();

 // PAST THIS LINE THE PROGRAM CHRASHES

}

the error
Unhandled exception at 0x581fad4a (msvcp100d.dll)
0xC0000005: Access violation reading location 0x00a94be4

if I switch to release the code runs just fine, pretty weird huh?

Hodgman

52,717

July 17, 2011 09:57 AM

It's not weird, it's common of bugs relating to uninitialized memory, or memory corruption -- the debug build includes extra checks to try and make bad code crash, so that you realize that you've got some kind of corruption going on.

Where/what is [font="Lucida Console"]_monster[/font]?

. 22 Racing Series .

bubu LV

1,436

July 17, 2011 09:57 AM

Is _monster really an object of class/struct GameMonster? And what type are Damage, Hp and Name members of _monster object?
Are there some other global variables with non-trivial constructor or destructor in your program?

SiCrane

11,840

July 17, 2011 09:57 AM

Whether or not it's weird depends on what your GameMonster type looks like. If it's non-POD, then it's not weird at all.

EvilNando

Author

July 17, 2011 10:09 AM

heres the full soruce

maybe something Im missing?







#include <iostream>

#include <string>

#include <sstream>

#include <iomanip>

#include <fstream>



using namespace std;



class GameMonster

{

public:

    string Name;

    int    Hp;

    int    Damage;



    GameMonster() { Name = ""; Hp = 0; Damage = 0; }

    GameMonster(string name, int hp, int dmg) { Name = name; Hp = hp; Damage = dmg; }

};





class GameNpc

{

public:

    string  Name;

    int     Hp;

    int     Damage;

    string  SpecialAttack;



    GameNpc() { Name = ""; Hp = 0; Damage = 0; SpecialAttack = ""; }

    GameNpc(string name, int hp, int dmg, string specialAtk) { Name = name; Hp = hp; Damage = dmg; SpecialAttack = specialAtk; }

};







void main()

{

    GameMonster _monster;

    GameMonster _monsters[3] = { GameMonster("Troll", 50, 20), GameMonster("Skeleton", 10, 5), GameMonster("Rat", 5, 1) };    

    GameNpc     _npcs[3] = { GameNpc("Gawein", 100, 25, "Smity"), GameNpc("Vivi", 25, 5, "LulzSkillz"), GameNpc("Necro", 40, 2, "Raise Dead") };



    ofstream _file("GameData.dat", ios::binary);



    _file.write((char*)_monsters, sizeof(_monsters));



    _file.seekp(0, ios::end);

    cout<<"size of GameData.dat "<<_file.tellp()<<" bytes"<<endl<<endl;



    _file.close();    







    ifstream _file_input("GameData.dat", ios::binary);

    for (int _idx = 0; _idx < 3; _idx++)

    {        

        cout<<"size of Monster "<<sizeof(GameMonster)<<" ";

        cout<<"current seek pointer position :"<<_file_input.tellg()<<endl;



        //_file_input.seekg(_idx * sizeof(GameMonster));

        _file_input.read((char*)&_monster, sizeof(GameMonster));



        cout<<_monster.Damage<<" "<<_monster.Hp<<" "<<_monster.Name<<endl;        

    }  



    _file_input.close();



    cout<<"\nPress a key"<<endl;

    getchar();

}

SiCrane

11,840

July 17, 2011 10:22 AM

std::string is non-POD, and since your classes contain it, your classes are non-POD. This means that you can't just copy the bits that make it up to a file and read it back. You need to do actual serialization.

EvilNando

Author

July 17, 2011 10:25 AM

I dont understand what POD means, but I guess I should use fixed width char arrays?

SiCrane

11,840

July 17, 2011 10:32 AM

The first link when I put "POD C++" into google.

EvilNando

Author

July 17, 2011 10:39 AM

The links says nothing about how to fix the problem so Ill ask again

should I use fixed char arrays instead or is there an actual way of reading std::strings of variable size using ifstream

<div><br></div><div><br></div><div>edit: I just tried using very long strings just to test what happened if I varied each of the monsters actual byte size but it still working properly (without considering the crash at the end of program)</div>

bubu LV

1,436

July 17, 2011 11:10 AM

Does it really prints out string as it is in file? Even for long strings? (>30 chars)

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