所以,今天我正在编写一些单元测试,突然G给了我一个关于GNU C和我的一个名为major的成员函数的意外警告.为什么我不能在没有触发G的情况下拥有名为major的成员函数？

这是一个最低限度可行的测试片段：

// Any of these includes trigger the warnings
#include <random>
#include <cstdlib>

class my_class {
public:
    void major() const;
};

inline void my_class::major() const {}

int main(void) {
    my_class my_obj;
    my_obj.major();
    return 0;
}

这是编译的输出(使用g –std = c 14 -o test-gcc-major test-gcc-major.cpp)：

[flisboac@sonic ~]$uname -a && lsb_release -a && g++ -v && g++ --std=c++14 -o test-gcc-major test-gcc-major.cpp && ./test-gcc-major 
Linux sonic 4.12.10-1-ARCH #1 SMP PREEMPT Wed Aug 30 12:18:42 CEST 2017 x86_64 GNU/Linux
LSB Version:    1.4
Distributor ID: Arch
Description:    Arch Linux
Release:    rolling
Codename:   n/a
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/7.1.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc-multilib/src/gcc/configure --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/ --enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared --enable-threads=posix --enable-libmpx --with-system-zlib --with-isl --enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch --disable-libssp --enable-gnu-unique-object --enable-linker-build-id --enable-lto --enable-plugin --enable-install-libiberty --with-linker-hash-style=gnu --enable-gnu-indirect-function --enable-multilib --disable-werror --enable-checking=release --enable-default-pie --enable-default-ssp
Thread model: posix
gcc version 7.1.1 20170630 (GCC) 
test-gcc-major.cpp:7:13: warning: In the GNU C Library, "major" is defined
 by <sys/sysmacros.h>. For historical compatibility, it is
 currently defined by <sys/types.h> as well, but we plan to
 remove this soon. To use "major", include <sys/sysmacros.h>
 directly. If you did not intend to use a system-defined macro
 "major", you should undefine it after including <sys/types.h>.
  void major() const;
             ^~~~~~~~                                                                                                                                                                                                                                                                                                                                                                
test-gcc-major.cpp:10:13: warning: In the GNU C Library, "major" is defined
 by <sys/sysmacros.h>. For historical compatibility, it is
 currently defined by <sys/types.h> as well, but we plan to
 remove this soon. To use "major", include <sys/sysmacros.h>
 directly. If you did not intend to use a system-defined macro
 "major", you should undefine it after including <sys/types.h>.
 inline void my_class::major() const {}
             ^~~~~~~~~~~~~~~~~~~~~~~~~~                                                                                                                                                                                                                                                                                                                                              
test-gcc-major.cpp:14:13: warning: In the GNU C Library, "major" is defined
 by <sys/sysmacros.h>. For historical compatibility, it is
 currently defined by <sys/types.h> as well, but we plan to
 remove this soon. To use "major", include <sys/sysmacros.h>
 directly. If you did not intend to use a system-defined macro
 "major", you should undefine it after including <sys/types.h>.
  my_obj.major();

以任何方式触发引用成员函数的每一行的警告.此外,我无法取消任何内容,因为我正在实施一个库,这个负担应归入最终用户.

那么,有人知道为什么要提出这个警告吗？我甚至没有在我的代码中的任何地方使用C.我正在使用的是< random>,它本身不是C(但可能包括“C”库,谁知道？).

在任何情况下,有没有办法在编译时检测需要和取消定义主要内容(例如使用一些预处理器巫术)？

更新：我正在使用< random>,而不是< cstdlib>.我刚刚发现< cstdlib>也会触发警告.

解决方法:

可以取消定义宏,这里仅用于向后兼容,很快就会删除,并且不应该首先出现在那里.这个#undef无法破坏或损害用户代码.

如果您的用户需要宏和您的标题包含在同一源文件中,请让他们自己排序.无论如何,无论你是否包含违规标题以及是否#undef,他们都必须这样做.