I have a Ubuntu 20.04.2 LTS machine and have gcc 9.4.0 by default.
I built a GCC-12.1.0 from source and wrote a very simple cpp program and compiled it with /path_to_gcc12_bin/g++.
Then I run gdb to follow, by pressing s, and it shows the program includes the newer version c++ header files of gcc12.
The shared library libstdc++.so.6 is still linked to the system path one.
My question is :
How does /path_to_gcc12_bin/g++ knows to use the newer version(its own) header files?
I don't have CPLUS_INCLUDE_PATH env variables or anything similar set up.
If I build the program using the system g++, it would use system path include files, that is /usr/include/c++/9/bits/regex.h.
P.S. move /path_to_gcc12 the whole directory to somewhere else, g++ can still include the newer header files correctly.
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
