ifstream 无缘无故失败？

Question

我有一个 3d 球体列表，当我保存列表时，我循环：

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

当我恢复列表时，我使用：

    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];
        .....   
    }

我不知道出了什么问题，但是在读取最后一行时，最后一行的颜色分量无法读取球体，读取最后一个球体的半径后流失败。我检查了球体列表文件：

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 

这看起来不错。有人能告诉我为什么会发生这种情况吗？这是ifstream的bug吗？ 顺便说一句，我正在使用 Unicode。

---

循环附在下面：

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);
    }
    */
}

Answer 1

我预计在正确读取 5 个球（球体）后会失败。

该循环的设计使得尝试读取第 6 个球将会失败，但 Add() 仍会被调用！
你应该重新定义你的代码：

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。空白是你的朋友。我个人认为这样更容易阅读：

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