[Solved] failed to compile cpp code with stdc++17

[Nitr0Cao]

As the title mentioned, I wrote a simple c++ code to test whether gcc-c++-8.3.1 works fine with stdc++17, but failed.

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➜ rpm -qa | grep c++
libstdc++-devel-8.3.1-5.el8.0.2.x86_64
ncurses-c++-libs-6.1-7.20180224.el8.x86_64
gcc-c++-8.3.1-5.el8.0.2.x86_64
libstdc++-8.3.1-5.el8.0.2.x86_64

Code:

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#include <filesystem>

int main(int argc, char *argv[]) {
    std::filesystem::path p("/root");
    std::filesystem::path p2("/usr");
    if (p != p2)
        return 0;
    else
        return 1;
}

command:

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g++ -v -std=c++17 -o test_cpp test_cpp.cpp

output:

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Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/8/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,fortran,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl --disable-libmpx --enable-offload-targets=nvptx-none --without-cuda-driver --enable-gnu-indirect-function --enable-cet --with-tune=generic --with-arch_32=x86-64 --build=x86_64-redhat-linux
Thread model: posix
gcc version 8.3.1 20191121 (Red Hat 8.3.1-5) (GCC)
COLLECT_GCC_OPTIONS='-v' '-std=c++17' '-o' 'test_cpp' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
 /usr/libexec/gcc/x86_64-redhat-linux/8/cc1plus -quiet -v -D_GNU_SOURCE test_cpp.cpp -quiet -dumpbase test_cpp.cpp -mtune=generic -march=x86-64 -auxbase test_cpp -std=c++17 -version -o /tmp/ccfaNEb9.s
GNU C++17 (GCC) version 8.3.1 20191121 (Red Hat 8.3.1-5) (x86_64-redhat-linux)
        compiled by GNU C version 8.3.1 20191121 (Red Hat 8.3.1-5), GMP version 6.1.2, MPFR version 3.1.6-p2, MPC version 1.0.2, isl version isl-0.16.1-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring nonexistent directory "/usr/lib/gcc/x86_64-redhat-linux/8/include-fixed"
ignoring nonexistent directory "/usr/lib/gcc/x86_64-redhat-linux/8/../../../../x86_64-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/x86_64-redhat-linux/8/../../../../include/c++/8
 /usr/lib/gcc/x86_64-redhat-linux/8/../../../../include/c++/8/x86_64-redhat-linux
 /usr/lib/gcc/x86_64-redhat-linux/8/../../../../include/c++/8/backward
 /usr/lib/gcc/x86_64-redhat-linux/8/include
 /usr/local/include
 /usr/include
End of search list.
GNU C++17 (GCC) version 8.3.1 20191121 (Red Hat 8.3.1-5) (x86_64-redhat-linux)
        compiled by GNU C version 8.3.1 20191121 (Red Hat 8.3.1-5), GMP version 6.1.2, MPFR version 3.1.6-p2, MPC version 1.0.2, isl version isl-0.16.1-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 6bc037fd95a01018b18727df05c3a70b
COLLECT_GCC_OPTIONS='-v' '-std=c++17' '-o' 'test_cpp' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
 as -v --64 -o /tmp/ccgGVSgW.o /tmp/ccfaNEb9.s
GNU assembler version 2.30 (x86_64-redhat-linux) using BFD version version 2.30-73.el8
COMPILER_PATH=/usr/libexec/gcc/x86_64-redhat-linux/8/:/usr/libexec/gcc/x86_64-redhat-linux/8/:/usr/libexec/gcc/x86_64-redhat-linux/:/usr/lib/gcc/x86_64-redhat-linux/8/:/usr/lib/gcc/x86_64-redhat-linux/
LIBRARY_PATH=/usr/lib/gcc/x86_64-redhat-linux/8/:/usr/lib/gcc/x86_64-redhat-linux/8/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/usr/lib/gcc/x86_64-redhat-linux/8/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-std=c++17' '-o' 'test_cpp' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
 /usr/libexec/gcc/x86_64-redhat-linux/8/collect2 -plugin /usr/libexec/gcc/x86_64-redhat-linux/8/liblto_plugin.so -plugin-opt=/usr/libexec/gcc/x86_64-redhat-linux/8/lto-wrapper -plugin-opt=-fresolution=/tmp/cc3lfHnJ.res -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lc -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc --build-id --no-add-needed --eh-frame-hdr --hash-style=gnu -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o test_cpp /usr/lib/gcc/x86_64-redhat-linux/8/../../../../lib64/crt1.o /usr/lib/gcc/x86_64-redhat-linux/8/../../../../lib64/crti.o /usr/lib/gcc/x86_64-redhat-linux/8/crtbegin.o -L/usr/lib/gcc/x86_64-redhat-linux/8 -L/usr/lib/gcc/x86_64-redhat-linux/8/../../../../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/usr/lib/gcc/x86_64-redhat-linux/8/../../.. /tmp/ccgGVSgW.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/x86_64-redhat-linux/8/crtend.o /usr/lib/gcc/x86_64-redhat-linux/8/../../../../lib64/crtn.o
/tmp/ccgGVSgW.o: In function `std::filesystem::__cxx11::operator==(std::filesystem::__cxx11::path const&, std::filesystem::__cxx11::path const&)':
test_cpp.cpp:(.text._ZNSt10filesystem7__cxx11eqERKNS0_4pathES3_[_ZNSt10filesystem7__cxx11eqERKNS0_4pathES3_]+0x1f): undefined reference to `std::filesystem::__cxx11::path::compare(std::filesystem::__cxx11::path const&) const'
/tmp/ccgGVSgW.o: In function `std::filesystem::__cxx11::path::path<char [6], std::filesystem::__cxx11::path>(char const (&) [6], std::filesystem::__cxx11::path::format)':
test_cpp.cpp:(.text._ZNSt10filesystem7__cxx114pathC2IA6_cS1_EERKT_NS1_6formatE[_ZNSt10filesystem7__cxx114pathC5IA6_cS1_EERKT_NS1_6formatE]+0x5e): undefined reference to `std::filesystem::__cxx11::path::_M_split_cmpts()'
/tmp/ccgGVSgW.o: In function `std::filesystem::__cxx11::path::path<char [5], std::filesystem::__cxx11::path>(char const (&) [5], std::filesystem::__cxx11::path::format)':
test_cpp.cpp:(.text._ZNSt10filesystem7__cxx114pathC2IA5_cS1_EERKT_NS1_6formatE[_ZNSt10filesystem7__cxx114pathC5IA5_cS1_EERKT_NS1_6formatE]+0x5e): undefined reference to `std::filesystem::__cxx11::path::_M_split_cmpts()'
collect2: error: ld returned 1 exit status

[jlehtone]

Those are linker errors.

The release notes of GCC 9 mention that 'stdc++fs' is linked automatically, when you use <filesystem>.
Therefore, GCC 8 does not do that.

You have to tell -lstdc++fs to compiler.

The other option is to install gcc-devtoolset-9-toolchain from AppStream. That should give you GCC 9.

[Nitr0Cao]

Thanks for your reply. Your answer solved my problem.
BTW, the package name is gcc-toolset-9-toolchain