封面发现：无法恢复ostream格式（STREAM_FORMAT_STATE） [英] Coverity finding: Not restoring ostream format (STREAM_FORMAT_STATE)

问题描述

我们正在寻找Coverity查找 CID 156014：无法恢复ostream格式（STREAM_FORMAT_STATE） （下面的文字和最后的图片）。

  938 const std :: streamsize oldp = cout.precision（6）; 
 5. format_changed：setf更改类型floatfield的std :: cout的格式状态。 
 939 const std :: ios :: fmtflags oldf = cout.setf（std :: ios :: fixed，std :: ios :: floatfield）; 
 940 cout<< Maurer Randomness Test returns value< mv < endl; 
 6. format_changed：precision更改std :: cout的格式状态以获取类别精度。 
 941 cout.precision（oldp）; 
 7. format_restored：setf更改类型floatfield的std :: cout的格式状态。 
 942 cout.setf（oldf，std :: ios :: floatfield）; 
  

出现第941行， cout.precision（oldp）是一个问题。 Coverity似乎将其分为 更改 ，而不是恢复 。

根据

我最近累了下面的内容，但它继续产生这个结果 format_changed：setf更改std的格式状态：

  //封面找寻$ 
 b $ b class StreamState 
 {
 public：
 StreamState（std :: ostream& out）
：m_out（out），m_fmt（out.flags（）），m_prec out.precision（））
 {
} 
 
〜StreamState（）
 {
 m_out.precision 
 m_out.flags（m_fmt）; 
} 
 
 private：
 std :: ostream& m_out; 
 std :: ios_base :: fmtflags m_fmt; 
 std :: streamsize m_prec; 
}; 
 ... 
 
 StreamState ss（cout）; 
 cout.setf（std :: ios :: fixed，std :: ios :: floatfield）; 
 cout.precision（6）; 
 
 cout<< Maurer Randomness Test returns value< mv < endl; 
  




解决方案

我们提交的一周），我们不能 使用成员函数在程序中设置 floatfield 即 ostream.iosflags（...）; ostream.precision（...） ）。我们不得不使用 floatfield （即 ostream<< setiosflags（...） < setprecision（...） ）：

  / Coverity查找
类StreamState 
 {
 public：
 StreamState（std :: ostream& out）
：m_out（out），m_fmt（out.flags ），m_prec（out.precision（））
 {
} 
 
〜StreamState（）
 {
 m_out.precision 
 m_out.flags（m_fmt）; 
} 
 
 private：
 std :: ostream& m_out; 
 std :: ios_base :: fmtflags m_fmt; 
 std :: streamsize m_prec; 
}; 
  

和：

  StreamState ss（cout）; 
 cout< std :: setiosflags（std :: ios :: fixed）<< std :: setprecision（6）; 
 cout< Maurer Randomness Test returns value< mv < endl; 
  




We are catching a Coverity finding CID 156014: Not restoring ostream format (STREAM_FORMAT_STATE) (text below and image at the end).

 938        const std::streamsize oldp = cout.precision(6);
    5. format_changed: setf changes the format state of std::cout for category floatfield.
 939        const std::ios::fmtflags oldf = cout.setf(std::ios::fixed, std::ios::floatfield);
 940        cout << "  Maurer Randomness Test returned value " << mv << endl;
    6. format_changed: precision changes the format state of std::cout for category precision.
 941        cout.precision(oldp);
    7. format_restored: setf changes the format state of std::cout for category floatfield.
 942        cout.setf(oldf, std::ios::floatfield);

It appears line 941, cout.precision(oldp) is an issue. Coverity seems to classify it as a change rather than a restore.

According to set back default precision C++ on SO, I believe we are doing what is recommended. (But I could be wrong, or the accepted answer may not be a best practice).

How can we restore precision and squash the Coverity finding?

---

---

I recently tired the following, but it continues to produce the finding format_changed: setf changes the format state of std::cout for category floatfield.

// Coverity finding
class StreamState
{
public:
    StreamState(std::ostream& out)
        : m_out(out), m_fmt(out.flags()), m_prec(out.precision())
    {
    }

    ~StreamState()
    {
        m_out.precision(m_prec);
        m_out.flags(m_fmt);
    }

private:
    std::ostream& m_out;
    std::ios_base::fmtflags m_fmt;
    std::streamsize m_prec;
};
...

StreamState ss(cout);
cout.setf(std::ios::fixed, std::ios::floatfield);
cout.precision(6);

cout << "  Maurer Randomness Test returned value " << mv << endl;

解决方案

After about 6 attempts (I think we used all of our submissions for the week), it appears we cannot use the member functions to set the floatfield in the program (i.e., ostream.iosflags(...); ostream.precision(...)). We had to use the manipulators for the floatfield (i.e., ostream << setiosflags(...) << setprecision(...)):

// Coverity finding
class StreamState
{
public:
    StreamState(std::ostream& out)
        : m_out(out), m_fmt(out.flags()), m_prec(out.precision())
    {
    }

    ~StreamState()
    {
        m_out.precision(m_prec);
        m_out.flags(m_fmt);
    }

private:
    std::ostream& m_out;
    std::ios_base::fmtflags m_fmt;
    std::streamsize m_prec;
};

And:

StreamState ss(cout);
cout << std::setiosflags(std::ios::fixed) << std::setprecision(6);
cout << "  Maurer Randomness Test returned value " << mv << endl;

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