__linux__、__POSIX__宏

　　__linux__用於定義linux，__POSIX__不太了解，各系統的宏有如下：

std::string getOsName() { #ifdef _WIN32 return "Windows 32-bit"; #elif _WIN64
    return "Windows 64-bit"; #elif __APPLE__ || __MACH__
    return "Mac OSX"; #elif __linux__
    return "Linux"; #elif __FreeBSD__
    return "FreeBSD"; #elif __unix || __unix__
    return "Unix"; #else
    return "Other"; #endif }