当默认标准为 201402L (c++14) 时，g++ 是否与 g++ -std=c++14 不同？
[英]Is g++ different than g++ -std=c++14 when the default standard is 201402L (c++14)?
问题描述
I was trying to make use of precompiled headers to speed up compilation following this link: https://codeforces.com/blog/entry/53909
我试图利用预编译的头文件来加快以下链接的编译速度： https://codeforces.com/blog/entry/53909
I observed that pre-compilation of headers and subsequent compilation of.cpp programs have to be done using the same g++ flags for the speed-up to work, which makes sense.我观察到头文件的预编译和.cpp 程序的后续编译必须使用相同的 g++ 标志来完成，以加快工作速度，这是有道理的。 However, explicitly setting the c++ standard to the default one did not work.但是，将 c++ 标准显式设置为默认值不起作用。 So, neither of pre-compilation using g++ stdc++.h and subsequent g++ -std=c++14 program.cpp , nor, g++ -std=c++14 and g++ program.cpp worked. So, neither of pre-compilation using g++ stdc++.h and subsequent g++ -std=c++14 program.cpp , nor, g++ -std=c++14 and g++ program.cpp worked.
This didn't make sense to me as I knew that my compiler, x86_64-w64-mingw32-g++.exe (gcc version 10.2.0), by default, conforms to 201402L (c++14) standard, which I figured using g++ -dM -E -x c++ /dev/null | fgrep __cplusplus这对我来说没有意义，因为我知道我的编译器 x86_64-w64-mingw32-g++.exe（gcc 版本 10.2.0）默认符合 201402L（c++14）标准，我想使用g++ -dM -E -x c++ /dev/null | fgrep __cplusplus g++ -dM -E -x c++ /dev/null | fgrep __cplusplus , and getting the following response: g++ -dM -E -x c++ /dev/null | fgrep __cplusplus ，并得到以下响应：
#define __cplusplus 201402L
So, my question is, what is the difference between g++ and g++ -std=c++14 when g++, by default, adheres to 201402L?所以，我的问题是，g++ 和 g++ -std=c++14 之间有什么区别，默认情况下，遵守 L2？ Also, is it significant enough for me to specifically opt for either one of them?另外，对我来说，专门选择其中任何一个是否足够重要？
1 个解决方案
解决方案1
2 已采纳 2021-04-19 20:08:43
GCC doesn't compile with -std=c++14 by default. GCC 默认不使用-std=c++14编译。 The description of the -std flag from the GCC man pages (for version 9.3.0) says GCC 手册页（对于版本 9.3.0）中-std标志的描述说
-std=Determine the language standard.-std=确定语言标准。 This option is currently only supported when compiling C or C++.The compiler can accept several base standards, such as c90 or c++98, and GNU dialects of those standards, such as gnu90 or gnu++98.
.
A value for this option must be provided;
.
c++14
c++1y
The 2014 ISO C++ standard plus amendments.
gnu++14
gnu++1y
GNU dialect of -std=c++14.
.
Emphasis mine.强调我的。 The current default is -std=gnu++14 , which targets the C++14 standard while also enabling GNU extensions to the C++ language.当前默认值为-std=gnu++14 ，它以 C++14 标准为目标，同时还启用了对 C++ 语言的GNU 扩展。 The distinction between the -std=c++XX flags and the -std=gnu++XX flags is explained further in What are the differences between -std=c++11 and -std=gnu++11? -std=c++XX标志和-std=gnu++XX标志之间的区别在 -std=c++11 和 -std=gnu++11 之间有什么区别？ . .
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