ifstream fails without any reason?

Question

I have a list of 3d spheres, when I save the list, I loop through:

void Facade::Save(std::ostream& fs)
{
    fs<<x<<" "<<y<<" "<<z<<" "<<r<<" "; //save fields
    fs<<color[0]<<" "<<color[1]<<" "<<color[2]<<std::endl;
}

and when I restore the list, I use:

    void Facade::Load(std::ifstream& fs, BallList* blist)
    {
        GLfloat c[3];
        fs>>x>>y>>z>>r;
        //fails there, why
        fs>>c[0]>>c[1]>>c[2];
        .....   
    }

I don't know what goes wrong, but when reading the last line, the color components of the last sphere cannot be read, the stream fails after reading the radius of the last sphere. I checked the sphere list file:

7.05008 8.99167 -7.16849 2.31024 1 0 0
3.85784 -3.93902 -1.46886 0.640751 1 0 0
9.33226 3.66375 -6.93533 2.25451 1 0 0
6.43361 1.64098 -6.17298 0.855785 1 0 0
6.34388 -0.494705 -6.88894 1.50784 1 0 0

This looks good. Can somebody tell me why is this happening? Is this a bug of ifstream? I'm using Unicode by the way.

The loops are attached below:

void BallList::Load(std::istream& fs)
{
    Clear();
    Facade ball1;
    while(!fs.fail() && !fs.eof())
    {
        ball1.Load(fs, this);
        Add(ball1);
    }
    /*
    balls.pop_back(); //this is a work around, get rid of the last one
    originalballs.pop_back();
    */
}

void BallList::Save(std::ostream& fs)
{
    vector<Facade>::iterator itero = this->originalballs.begin();
    while (itero != this->originalballs.end())
    {
        itero->Save(fs);
        itero++;
    }

    /*
    //work around the ifstream problem: the color of the last sphere cannot be read
    //add a dummy item as the last
    itero = this->originalballs.begin();
    if(itero != this->originalballs.end())
    {
        itero->Save(fs);
    }
    */
}

Please state what exactly you mean by "fails". Are you referring to the fail bit? — NPE, May 26 '11 at 16:42
@Bart (who suggested an edit): I think the title is more correct with the double negative than without. — Ben Voigt, May 26 '11 at 16:50
@Han: We need to see more code. You are probably doing this in some loop. Can you show us this loop? — Björn Pollex, May 26 '11 at 16:57
Your sphere list file seems to indicate that you wrote out the colors as integers and not floats. I wonder if changing "GLfloat c[3]" to "int c[3]" would make it work. — Sergio Martinez, May 26 '11 at 17:02
`ifstream` never "fails without any reason". You made a mistake. — Lightness Races in Orbit, May 26 '11 at 17:05
Thanks for your reply. But the color components are float numbers, 1 stands for brightest, which is 255 in GLubyte. — zhy2002, May 26 '11 at 17:06
I guess it's safer to say ifstream sometimes fails without an obvious reason. — zhy2002, May 26 '11 at 17:08

Martin York · Answer 1 · 2011-05-26T17:36:41.613

I would expect this to fail after reading 5 balls (spheres) correctly.

The loop is designed so that attempting to read the 6^th ball will fail but Add() is still called!! You should redefine your code a bit:

std::ifstream& Facade::Load(std::ifstream& fs, BallList* blist)
{
    GLfloat c[3];
    fs>>x>>y>>z>>r;        // This will fail if there is no input.
                           // Once all 5 balls have been read
                           // There is only a new line character on the stream.
                           // Thus the above line will fail and the fail bit is now set.
    fs>>c[0]>>c[1]>>c[2];

    return fs;  // returned so it can be tested in loop.
}

void BallList::Load(std::istream& fs)
{
    Clear();
    Facade ball1;
    while(ball1.Load(fs, this))  // Only enter loop if the load worked
    {                            // Load worked if the stream is in a good state.
        // Only call Add() if Load() worked.
        Add(ball1);
    }
}

PS. White space is your friend. Personally I think this is easier to read:

    fs >> x >> y >> z >> r;

ifstream fails without any reason?

1 Answers1