升壓日誌非const位域編譯錯誤（向後兼容問題）

Question

我把例如從http://www.boost.org/doc/libs/1_61_0/libs/log/example/doc/tutorial_trivial_flt.cpp並增加了一個位域打印：

#include <boost/log/core.hpp> 
#include <boost/log/trivial.hpp> 
#include <boost/log/expressions.hpp> 

namespace logging = boost::log; 

//[ example_tutorial_trivial_with_filtering 
void init() 
{ 
    logging::core::get()->set_filter 
    (
     logging::trivial::severity >= logging::trivial::info 
    ); 
} 


struct BF { 
       unsigned int b : 8; 
       BF() : b(0) {} 
}; 


int main(int, char*[]) 
{ 
    init(); 

    BF bf; 
    BOOST_LOG_TRIVIAL(info) << "An informational severity message " << bf.b; 

    return 0; 
} 
//] 

有了提升1.61我得到一個編譯錯誤：

cannot bind bitfield 'bf.BF::b' to 'unsigned int&'

使用boost 1.57編譯並運行代碼（打印：[2016-09-19 20：21：33.018112] [0x000007fd1d5be672] [info]信息嚴重性消息0）

注意：

1. 的課程COUT可以處理這個問題（所以我認爲這不僅是向後兼容的問題，而是一個bug）
2. 提升1.61可以處理常量位字段，例如BOOST_LOG_TRIVIAL(info) << "An informational severity message " << BF().b;

我正在尋找解決方法。 建議？

Answer 1

我找到了一個解決辦法 - 超載運營< <所有無符號整數record_ostream：

#include <sys/types.h> 

namespace logging = boost::log; 

typedef logging::basic_formatting_ostream<logging::record_ostream::char_type> formatting_ostream_type; 

logging::record_ostream& operator << (logging::record_ostream& strm, u_int8_t value) { 
    static_cast< formatting_ostream_type& >(strm) << value; 
    return strm; 
} 

logging::record_ostream& operator << (logging::record_ostream& strm, u_int16_t value) { 
    static_cast< formatting_ostream_type& >(strm) << value; 
    return strm; 
} 

logging::record_ostream& operator << (logging::record_ostream& strm, u_int32_t value) { 
    static_cast< formatting_ostream_type& >(strm) << value; 
    return strm; 
} 

logging::record_ostream& operator << (logging::record_ostream& strm, u_int64_t value) { 
    static_cast< formatting_ostream_type& >(strm) << value; 
    return strm; 
} 

的整數得到複製（採取按值），這樣就是沒有綁定問題

Answer 2

最簡單的解決方法是將位域轉換爲完整整數。你可以做到這一點與鑄造：

BOOST_LOG_TRIVIAL(info) << "An informational severity message " 
    << static_cast< unsigned int >(BF().b);