Linux 什么是 GCC 默认包含目录？

What are the GCC default include directories?

提问by Raxvan

When I compile a very simple source file with gcc I don't have to specify the path to standard include files such as stdio or stdlib.

当我用 gcc 编译一个非常简单的源文件时，我不必指定标准包含文件（如 stdio 或 stdlib）的路径。

How does GCC know how to find these files?

GCC 如何知道如何找到这些文件？

Does it have the /usr/includepath hardwired inside, or it will get the paths from other OS components?

它/usr/include内部是否有硬连线的路径，或者它会从其他操作系统组件获取路径？

采纳答案by Ihor Kaharlichenko

In order to figure out the default paths used by gcc/g++, as well as their priorities, you need to examine the output of the following commands:

为了找出gcc/使用的默认路径g++及其优先级，您需要检查以下命令的输出：

1. For C:

1. 对于C：

    gcc -xc -E -v -

1. For C++:

2. 对于C++：

    gcc -xc++ -E -v -

The credit goes to Qt Creator team.

归功于Qt Creator 团队。

回答by abyss.7

There is a command with a shorter output, which allows to automatically cut the include pathes from lines, starting with a single space:

有一个输出较短的命令，它允许自动从行中剪切包含路径，从一个空格开始：

$ echo | gcc -Wp,-v -x c++ - -fsyntax-only
ignoring nonexistent directory "/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include-fixed"
ignoring nonexistent directory "/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../x86_64-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2
 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/x86_64-redhat-linux
 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/backward
 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/include
 /usr/local/include
 /usr/include
End of search list.

The credit goes to the libc++ front-page.

功劳归于 libc++ front-page。

回答by Daniele Testa

Just run the following to list the default search paths:

只需运行以下命令即可列出默认搜索路径：

$(gcc -print-prog-name=cc1) -v

回答by hermannk

Though I agree with Ihor Kaharlichenko's answer for considering C++ and with abyss.7's answer for the compactness of its output, they are still incompletefor the multi-arch versions of gcc because input processing depends on the command line parameters and macros.

尽管我同意 Ihor Kaharlichenko 考虑 C++ 的回答以及 abyss.7 对其输出紧凑性的回答，但对于 gcc 的多架构版本，它们仍然不完整，因为输入处理取决于命令行参数和宏。

Example:

例子：

echo | /opt/gcc-arm-none-eabi-9-2019-q4-major/bin/arm-none-eabi-g++ -specs=nano.specs -mcpu=cortex-m4 -march=armv7e-m -mthumb -mfloat-abi=soft -x c++ -E -Wp,-v\ - -fsyntax-onlyyields

echo | /opt/gcc-arm-none-eabi-9-2019-q4-major/bin/arm-none-eabi-g++ -specs=nano.specs -mcpu=cortex-m4 -march=armv7e-m -mthumb -mfloat-abi=soft -x c++ -E -Wp,-v\ - -fsyntax-only产量

?
/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/../arm-none-eabi/include/newlib-nano                                                                                                              
/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/include/c++/9.2.1                                                                        
/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/include/c++/9.2.1/arm-none-eabi/thumb/v7e-m/nofp                                         
/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/include/c++/9.2.1/backward                                                               
/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/../lib/gcc/arm-none-eabi/9.2.1/include                                                                                                            
 /opt/gcc-arm-none-eabi-9-2019-q4-major/bin/../lib/gcc/arm-none-eabi/9.2.1/include-fixed                                                                                                      
/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/include                                                                                  
?

whereas echo | /opt/gcc-arm-none-eabi-9-2019-q4-major/bin/arm-none-eabi-g++ -x c++ -E -Wp,-v - -fsyntax-onlyyields

而echo | /opt/gcc-arm-none-eabi-9-2019-q4-major/bin/arm-none-eabi-g++ -x c++ -E -Wp,-v - -fsyntax-only产量

?
/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/include/c++/9.2.1                                                                        
/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/include/c++/9.2.1/arm-none-eabi                                                          
/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/include/c++/9.2.1/backward                                                               
/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/../lib/gcc/arm-none-eabi/9.2.1/include                                                                                                            
/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/../lib/gcc/arm-none-eabi/9.2.1/include-fixed                                                                                                      
/opt/gcc-arm-none-eabi-9-2019-q4-major/bin/../lib/gcc/arm-none-eabi/9.2.1/../../../../arm-none-eabi/include                                                                                  
?

The former invocation utilizes newlib(see lines 1 and 3 of the output), the latter goes with the standard includes. The common files at the end of the list are an example for the usage of include_next.

前者调用利用newlib（见输出的第 1 和第 3 行），后者与标准包含一起使用。列表末尾的公共文件是include_next.

Bottom line: Always consider all macrosand compiler optionswhen printing the include directories.

底线：在打印包含目录时始终考虑所有宏和编译器选项。