Program Crashes at Runtime, but doesn't crash when being stepped through.

RBrNx277

Hi there, I've been developing a QT application for the first time over the last couple of days and it's being going well. Today I added a regular C++ function to my program and tested it out.

If I remove the call to this function then the program will run perfectly with no crashes (but no new function of course)
If I place the call the function back into the program, then my program will crash at Runtime (When I click a button to start my program).
However, if I leave the function in the program, and place a breakpoint at the start of the function, I can step through my entire program until it finishes without a single crash.

Has anyone experience something like this before?

Here is the function that's causing the issue (I believe I'm getting an access violation error):

void SokoGenerator::rotatePattern(twoDVector *pattern, int rotation){
    twoDVector tempPattern = *pattern;
    if(rotation == 1){
        //Rotate by 90 - reverse each row
        for(int i = 0; i < tempPattern[i].size(); i++){
            std::reverse(tempPattern[i].begin(), tempPattern[i].end());
        }
        *pattern = tempPattern;
    }
    else if(rotation == 2){
        //Rotate by 180 - reverse each row, then each column
        for(int i = 0; i < tempPattern[i].size(); i++){
            std::reverse(tempPattern[i].begin(), tempPattern[i].end());
        }

        std::reverse(tempPattern.begin(), tempPattern.end());
        *pattern = tempPattern;
    }
    else if(rotation == 3){
        //Rotate by 270 - reverse each column
        std::reverse(tempPattern.begin(), tempPattern.end());
        *pattern = tempPattern;
    }
}

Quick background - 'twoDVector' is a type I created which is declared as:

typedef <vector <vector<char> > twoDVector;

Thanks, RBrNx277

kshegunov

Hello,
You are (probably) going out of bounds, that's why your program is crashing.

for(int i = 0; i < tempPattern[i].size(); i++)

Don't you mean?

for(int i = 0; i < tempPattern.size(); i++)

I'd like also to point out, that if you're doing:

twoDVector tempPattern = *pattern;
// ... Some code
*pattern = tempPattern;

Then it's best to use references and not pointers, also use switch and enums instead of if-else-if-else. Like this:

enum Rotation { Rotate90Degrees, Rotate180Degrees, Rotate270Degrees };

void SokoGenerator::rotatePattern(twoDVector & pattern, Rotation rotationFlag)
{
    switch (rotationFlag)
    {
    case Rotate90Degrees:
        for(qint32 i = 0, size = pattern.size(); i < size; i++)    //< Good idea to use a temporary for the size, no need to call the method every iteration
            std::reverse(pattern[i].begin(), pattern[i].end());
        break;
    case Rotate180Degrees:
        // ... More code
        break;
    default:  //< Handle incorrect flags here!
        cerr << "Error incorrect flag passed to SokoGenerator::rotatePattern";
    }
}

Looks a bit simpler without the pointer dereferencing, doesn't it?

Kind regards.