GCC的默认包含目录是什么？

当我使用gcc编译非常简单的源文件时，无需指定标准包含文件（例如stdio或stdlib）的路径。

GCC如何知道如何找到这些文件？

它/usr/include内部是否具有硬连线的路径，还是会从其他OS组件获取路径？

为了弄清楚gcc/ 所使用的默认路径g++及其优先级，您需要检查以下命令的输出：

1. 对于C：

    gcc -xc -E -v -

2. 对于C ++：

    gcc -xc++ -E -v -

这归功于Qt Creator团队。

有一个输出较短的命令，该命令允许从一个空格开始自动剪切行中的包含路径：

$ 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.

功劳归于libc ++ 主页。

尽管我同意Ihor Kaharlichenko关于考虑C ++的回答以及关于Abyss.7关于其输出紧凑性的回答，但对于gcc的多体系结构版本，它们仍然是不完整的，因为输入处理取决于命令行参数和宏。

例：

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                                                                                  
⋮

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

⋮
/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                                                                                  
⋮

前者调用利用newlib（请参见输出的第1和3行），后者与标准包含一起使用。列表末尾的通用文件是的用法示例include_next。

底线：打印包含目录时，请始终考虑所有宏和编译器选项。

只需运行以下命令以列出默认搜索路径：

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