Question

We have a custom Logging class which compiles fine in VisualStudio 2010, but throws errors when being compiled with g++ on Linux. The error message we receive are the following:

Logger.hpp:84: error: declaration of "operator<<" as non-function
Logger.hpp:84: error: expected ";" before "(" token
Logger.hpp:91: error: expected ";" before "inline"
Logger.hpp:91: error: declaration of "operator<<" as non-function
Logger.hpp:91: error: expected ";" before "(" token
Logger.hpp:98: error: expected ";" before "typedef"

The respective lines of code are the following:

/*:84*/inline Logger& operator<<(std::_Smanip<std::ios_base::fmtflags> output)
{
        if (this->loggingEnabled())
                std::cout << output;
        return *this;
}

inline Logger& operator<<(std::_Smanip<std::streamsize> output)
{
        if (this->loggingEnabled())
                std::cout << output;
        return *this;
}

typedef std::basic_ostream<char, std::char_traits<char> >& (*StdEndl)(std::basic_ostream<char, std::char_traits<char> >&);
inline Logger& operator<<(StdEndl output)
{
        if (this->loggingEnabled())
                std::cout << output;
        return *this;
}

Other methods overloading the << operator work fine, therefore my guess is that the errors have something to with the argument type (std::_Smanip); any clues as to why?

Thanks,
Ben

Answer 1

_Smanip is a Microsoft extension, and not part of the standard library. That’s why your code compiles under Visual C++.

Here’s an MSDN article on the use of _Smanip, and here’s another one of how to avoid using it and write portable code instead.

EDIT: Found another link that explains manipulators with parameters in great detail. They discuss methods to implement custom ones as well.