G++ 版本和标准选项

Question

I see one of my makefile and see the below command.

g++-5 -std=c++11 

From what I understand, the std option represents this -

GCC supports different dialects of C++, corresponding to the multiple published ISO standards. Which standard it implements can be selected using the -std= command-line option.

What does -5 in the g++ command signifies?

Answer 1

The 5 almost certainly means the version of GCC, 5.something in this case.

Having names like this makes it easier to mix different versions on the same system.

You can confirm this by running

g++ --version

and you should get something like

g++ (GCC) 5.2.0

You are correct about the -std option. In addition to released versions, there is often support for upcoming versions. You can find a summary of the support here and the options such as -std=c++2a for features planned for C++20 here .

Answer 2

g++ 旁边的参数 -n 表示您要编译代码的 GNU C++ 编译器版本

Answer 3

The -5 is part of the actual g++ executable's name. The exact choice of name is essentially up to the maintainers of your operating system or distribution. Naming the executable this way allows multiple GCC versions to be installed in parallel, a feature that is often useful, for example if you want to offer your software to a variety of users and want to make sure that different compiler versions can handle your code. For example, on one of my (slightly older) boxes I currently see

$ ls -l /usr/bin/g++*
lrwxrwxrwx 1 root root      7 Apr  8  2014 /usr/bin/g++ -> g++-4.8
-rwxr-xr-x 1 root root 259176 Mar 20  2014 /usr/bin/g++-4.4
-rwxr-xr-x 1 root root 775888 May  7  2016 /usr/bin/g++-4.8
$ /usr/bin/g++-4.4 --version
g++-4.4 (Ubuntu/Linaro 4.4.7-8ubuntu1) 4.4.7
Copyright (C) 2010 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ /usr/bin/g++-4.8 --version
g++-4.8 (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Different compiler versions not only have differing support regarding C++ standard features, they may also have different bugs or quirks.

Regarding GCC's support for different versions of the C++ standard, see https://gcc.gnu.org/projects/cxx-status.html . For example, some C++17 language features were only introduced in GCC 5.1.