我的自建gcc 12是如何知道包含gcc 12 c++头文件的，而不是使用系统路径包含文件？

Question

我有一台Ubuntu 20.04.2 LTS机器，默认情况下有gcc 9.4.0。

我从源代码中构建了一个GCC-12.1.0，并编写了一个非常简单的cpp程序，并使用/path_to_gcc12_bin/g++编译了它。

然后运行gdb，按下s，然后显示程序包含较新版本的gcc12 c++头文件。

共享库libstdc++.so.6仍然链接到系统路径1。

我的问题是：

/path_to_gcc12_bin/g++ 如何知道如何使用更新版本(它自己的)头文件？

我没有设置CPLUS_INCLUDE_PATH env变量或任何类似的设置。

如果我使用系统g++构建程序，它将使用系统路径包含文件，即/usr/include/c++/9/bits/regex.h。

P.S.将整个目录移动到其他地方，g++仍然可以正确地包含较新的头文件。

test.cpp

#include <iostream>
#include <regex>
using namespace std;

int main(){
    std::regex re("Get|GetValue");
    std::cmatch m;
    cout << std::regex_search("GetValue", m, re)  << endl;  // returns true, and m[0] contains "Get"
    cout << std::regex_match ("GetValue", m, re)  << endl;  // returns true, and m[0] contains "GetValue"
    cout << std::regex_search("GetValues", m, re)  << endl; // returns true, and m[0] contains "Get"
    cout << std::regex_match ("GetValues", m, re)  << endl; // returns false
}

tian@tian-B250M-Wind:~/GCC-12.1.0/bin$ LD_PRELOAD='/home/tian/GCC-12.1.0/lib64/libstdc++.so.6.0.30' gdb ./test
(gdb) b 9
Breakpoint 1 at 0x4036f7: file test.cpp, line 9.
(gdb) r
Starting program: /home/tian/GCC-12.1.0/bin/test 

Breakpoint 1, main () at test.cpp:9
9               cout << std::regex_search("GetValue", m, re)  << endl;  // returns true, and m[0] contains "Get"
(gdb) s
std::regex_search<char, std::allocator<std::__cxx11::sub_match<char const*> >, std::__cxx11::regex_traits<char> > (__s=0x42c0f6 "GetValue", __m=..., __e=..., __f=std::regex_constants::_S_default)
    at /home/tian/GCC-12.1.0/include/c++/12.1.0/bits/regex.h:2409
2409        { return regex_search(__s, __s + _Rx_traits::length(__s), __m, __e, __f); }

at /home/tian/GCC-12.1.0/include/c++/12.1.0/bits/regex.h:2409

Answer 1

我猜gcc和g++在相对目录中找到了相对于/path_to_gcc12/bin/gcc的标题。

无论我在哪里mv gcc12指令集在我的机器上。它始终可以正确地包含自己的c++头文件。

尝试./g++ -g -Wall --verbose -o test test.cpp给出了包含路径：

tian@tian-B250M-Wind:~/Desktop/GCC-12.1.0/bin$ ./g++ -g -Wall --verbose -o test test.cpp
Using built-in specs.
COLLECT_GCC=./g++
COLLECT_LTO_WRAPPER=/home/tian/Desktop/GCC-12.1.0/bin/../libexec/gcc/x86_64-pc-linux-gnu/12.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /home/tian/playground/gcc_build_play/objdir/../gcc-12.1.0/configure --prefix=/home/tian/GCC-12.1.0 --disable-multilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.1.0 (GCC) 
COLLECT_GCC_OPTIONS='-g' '-Wall' '-v' '-o' 'test' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
 /home/tian/Desktop/GCC-12.1.0/bin/../libexec/gcc/x86_64-pc-linux-gnu/12.1.0/cc1plus -quiet -v -imultiarch x86_64-linux-gnu -iprefix /home/tian/Desktop/GCC-12.1.0/bin/../lib/gcc/x86_64-pc-linux-gnu/12.1.0/ -D_GNU_SOURCE test.cpp -quiet -dumpbase test.cpp -dumpbase-ext .cpp -mtune=generic -march=x86-64 -g -Wall -version -o /tmp/ccrg0qhG.s
GNU C++17 (GCC) version 12.1.0 (x86_64-pc-linux-gnu)
        compiled by GNU C version 12.1.0, GMP version 6.2.1, MPFR version 4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring nonexistent directory "/home/tian/Desktop/GCC-12.1.0/bin/../lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../x86_64-pc-linux-gnu/include"
ignoring duplicate directory "/home/tian/Desktop/GCC-12.1.0/bin/../lib/gcc/../../lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../include/c++/12.1.0"
ignoring duplicate directory "/home/tian/Desktop/GCC-12.1.0/bin/../lib/gcc/../../lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../include/c++/12.1.0/x86_64-pc-linux-gnu"
ignoring duplicate directory "/home/tian/Desktop/GCC-12.1.0/bin/../lib/gcc/../../lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../include/c++/12.1.0/backward"
ignoring duplicate directory "/home/tian/Desktop/GCC-12.1.0/bin/../lib/gcc/../../lib/gcc/x86_64-pc-linux-gnu/12.1.0/include"
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring duplicate directory "/home/tian/Desktop/GCC-12.1.0/bin/../lib/gcc/../../lib/gcc/x86_64-pc-linux-gnu/12.1.0/include-fixed"
ignoring nonexistent directory "/home/tian/Desktop/GCC-12.1.0/bin/../lib/gcc/../../lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../x86_64-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /home/tian/Desktop/GCC-12.1.0/bin/../lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../include/c++/12.1.0
 /home/tian/Desktop/GCC-12.1.0/bin/../lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../include/c++/12.1.0/x86_64-pc-linux-gnu
 /home/tian/Desktop/GCC-12.1.0/bin/../lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../include/c++/12.1.0/backward
 /home/tian/Desktop/GCC-12.1.0/bin/../lib/gcc/x86_64-pc-linux-gnu/12.1.0/include
 /home/tian/Desktop/GCC-12.1.0/bin/../lib/gcc/x86_64-pc-linux-gnu/12.1.0/include-fixed
 /usr/local/include
 /home/tian/Desktop/GCC-12.1.0/bin/../lib/gcc/../../include
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.

关于https://stackoverflow.com/a/72762087/5983841的更多细节