please explain this runtime error if you can?

[iw0XoG1T]

I wrote a program that had these two functions

std::string line_format_for_total ( const std::string title,
                                    const long long val )
{
    std::stringstream ss;
    std::string rt ;
    ss << title ;
    ss << std::setw(FIELD_WIDTH_SZ) ;
    ss << format_with_commas ( val / 100.0 , 2 );
    ss.flush () ;

    rt = ss.str();
//  return ss.str(); <---this is how it was originally written.
    return rt;
}

std::string line_format_for_col   ( const std::string  title1,
                                    const std::string  title2 )
{
    std::stringstream ss;
    std::string rt ;
    ss << title1 ;
    ss << center_on(title2, FIELD_WIDTH_SZ) ;
    ss.flush () ;

    rt = ss.str();
//  return ss.str(); <---this is how it was originally written.
    return rt;

}

These functions work, but when written the original way they would work if one was called but not if they were both called.

I spent at least five hours trying to figure out what was wrong; because why it broke made no sense to me. If I call only one of the functions in the program or tested them separately there was no problem.

[ne555]

http://www.cplusplus.com/forum/articles/40071/#msg216313

[iw0XoG1T]

@ness555 I'll try to explain with more detail.

chwsks wrote:

These functions work, but when written the original way they would work if one was called but not if they were both called.

* If a comment-out either function call the program will run without error.

*But when I try to call them both the program does not run.

* If you look at the code I wrote you will see I placed a comment that shows how they were originally written. It is a runtime error the program compiles without error, but when written the original way it is stopped by the operating system with a message that says the program has been stopped.

* More confusing is the fact that when I run this same program at home I can run it either way and they both work. I did recompile the program so it is not the same program--but both were compiled with the same compiler (gcc-4.7.0).

* I would also appreciate a little more detailed criticism because I really do not understand why you feel that this question was not asked in the smart way.

[ne555]

You are incurring in undefined behaviour.
Those functions are fine, the problem is somewhere else. format_with_commas() center_on() or the caller code

[iw0XoG1T]

problem is somewhere else. format_with_commas() center_on()

I did not write the format_with_commas I copied from somewhere--I actually do not
understand why it works. If it is the problem I can rewrite that function more simply.

I probably should not use code I don't personally understand.

I posted the code below in hope that maybe someone else can spot the problem.

std::string center_on (  std::string in, unsigned col_sz)
{
    unsigned left_pad = ( col_sz - in.size () ) / 2 ;
    unsigned right_pad =  col_sz - in.size () - left_pad; 
    std::string lp; 

    for( unsigned i = 0 ; i != left_pad ; ++ i)
        lp += ' ' ;
    
    lp += in ;

    for( unsigned i = 0 ; i != right_pad ; ++ i)
        lp += ' ' ;
    
    return lp ; 

class comma_numpunct : public std::numpunct<char>
{
protected:
    virtual char do_thousands_sep () const
    {
        return ',' ;
    }

    virtual std::string do_grouping () const
    {
        return "\03" ;
    }
};

template<class T>
std::string format_with_commas (T value, unsigned precision)
{
    std::locale comma_locale (std::locale () ,
                              new comma_numpunct ()) ;
    std::stringstream ss ;
    ss.imbue (comma_locale) ;
    ss << std::setprecision (precision)
       << std::fixed << value ;
    return ss.str () ;
}
}