Coverity finding: Not restoring ostream format (STREAM_FORMAT_STATE)

问题:

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?

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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; 

回答1:

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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