只要重载operator << (std::ostream&, ...)
,formatting_ostream
就没有问题。
template< typename CharT, typename TraitsT, typename AllocatorT, typename T >
inline basic_formatting_ostream< CharT, TraitsT, AllocatorT >&
operator<< (basic_formatting_ostream< CharT, TraitsT, AllocatorT >& strm, T const& value)
{
strm.stream() << value;
return strm;
}
stream()
函数返回std::ostream&
。如果你重载了第一个参数为formatting_ostream
的operator <<
,那么只能与boost::log
一起使用;如果你重载了std::ostream&
,那么可以用于boost::log
和其他输出。
引用头文件中的一句话:
* This stream wrapper is used by the library for log record formatting. It implements the standard string stream interface
* with a few differences:
*
* \li It does not derive from standard types <tt>std::basic_ostream</tt>, <tt>std::basic_ios</tt> and <tt>std::ios_base</tt>,
* although it tries to implement their interfaces closely. There are a few small differences, mostly regarding <tt>rdbuf</tt>
* and <tt>str</tt> signatures, as well as the supported insertion operator overloads. The actual wrapped stream can be accessed
* through the <tt>stream</tt> methods.
* \li By default, \c bool values are formatted using alphabetical representation rather than numeric.
* \li The stream supports writing strings of character types different from the stream character type. The stream will perform
* character code conversion as needed using the imbued locale.
* \li The stream operates on an external string object rather than on the embedded one. The string can be attached or detached
* from the stream dynamically.
*
* Although <tt>basic_formatting_ostream</tt> does not derive from <tt>std::basic_ostream</tt>, users are not required to add
* special overloads of \c operator<< for it since the stream will by default reuse the operators for <tt>std::basic_ostream</tt>.
* However, one can define special overloads of \c operator<< for <tt>basic_formatting_ostream</tt> if a certain type needs
* special formatting when output to log.
std::ostream
的优点应该非常明显:您也可以将其用于“正常”输出。 :) - Some programmer dude