Compilation issues when using #include<filesystem>

[pingal]

Here is my .pro

QT -= gui

CONFIG += c++17
CONFIG += console
CONFIG -= app_bundle

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += \
        main.cpp

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

Here is my main.cpp

#include <QCoreApplication>
#include <filesystem>


int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    return a.exec();
}

Here is the compiler output

g++ -c -fno-keep-inline-dllexport -g -std=gnu++1z -Wall -Wextra -Wextra -fexceptions -mthreads -DUNICODE -D_UNICODE -DWIN32 -DMINGW_HAS_SECURE_API=1 -DQT_QML_DEBUG -DQT_CORE_LIB -I../test -I. -IC:/Qt/6.0.4/mingw81_64/include -IC:/Qt/6.0.4/mingw81_64/include/QtCore -Idebug -IC:/Qt/6.0.4/mingw81_64/mkspecs/win32-g++  -o debug\main.o ..\test\main.cpp
In file included from C:/Qt/Tools/mingw810_64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/filesystem:37,
                 from ..\test\main.cpp:2:
C:/Qt/Tools/mingw810_64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/bits/fs_path.h: In member function 'std::filesystem::__cxx11::path& std::filesystem::__cxx11::path::operator/=(const std::filesystem::__cxx11::path&)':
C:/Qt/Tools/mingw810_64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/bits/fs_path.h:237:47: error: no match for 'operator!=' (operand types are 'std::filesystem::__cxx11::path' and 'std::filesystem::__cxx11::path')
    || (__p.has_root_name() && __p.root_name() != root_name()))

[Kent-Dorfman]

see the compiler notes here -> https://en.cppreference.com/w/cpp/filesystem

[pingal]

Thanks for the reply.

According to the link "Using this library may require additional compiler/linker options. GNU implementation prior to 9.1 requires linking with -lstdc++fs and LLVM implementation prior to LLVM 9.0 requires linking with -lc++fs"

So i added the following lines in .pro file

LIBS += -lstdc++fs

Still the same output.

P.S: I also tried

LIBS += -lc++fs

But the problem persists

[JonB]

@pingal
I do not know what precisely you are supposed to do here. But the errors you show earlier are compilation errors, so adding linker flags is not going to resolve that....

[pingal]

@JonB exactly, that's the compilation errors and has nothing to do with the linker but i followed notes Kent-Dorfman has suggested

I think this is some sort of bug (when std::filesystem is used in QT)

[JonB]

@pingal said in Compilation issues when using #include<filesystem>:

I think this is some sort of bug (when std::filesystem is used in QT)

Well you could test that in a standalone program without Qt?

I have seen possible issues like https://www.reddit.com/r/cpp_questions/comments/f10d31/comment/fh11qat/?utm_source=reddit&utm_medium=web2x&context=3

Your issue is most likely with MINGW. Its GCC may not be complete/up-to-date.

Maybe you could play at https://godbolt.org/ ?

[Axel Spoerl]

Your compiler version (mingw8.1.0) is not suitable for the Qt version you are trying to compile with (6.0.2).
See here for an overview.
More specifically: for the MinGW version you use, you have to #include<experimental/filesystem> which is why you get the error.
With more recent compilers (e.g. GCC10 or MinGW 11.2), -lstdc++fs is no longer necessary. If the missing linking instruction was the problem, you'd have had a linker rather than a compiler error.
BRgds
Axel

[pingal]

@Axel-Spoerl That really helped.

I've added QT 6.2.3 along with MinGW 9.0.0 to QT Creator and the problem is solved.

[rowan Samy]

@pingal how did you fix this bug I have the same issue

[JonB]

@rowan-Samy
Since @pingal already wrote

I've added QT 6.2.3 along with MinGW 9.0.0 to QT Creator and the problem is solved.

what have you done?

[rowan Samy]

This post is deleted!

[rowan Samy]

This post is deleted!

[JonB]

@rowan-Samy
Seriously?

1. Install Qt 6.2.3.
2. Install (may come with the Qt version) and use (select as kit) MinGW 9.0.0.
3. See whether your problem has gone away.

If not then it appears you have a different problem from @pingal so there's no point asking him what he did.