Why does GCC not seem to have the filesystem standard library?

Question

i'm facing a problem with filesystem library, it should be included in c++17 compiler, after 2 days i tried to install gcc-7.0.2 in raspberry pi but it didn't work, it couldn't recognize the command gcc-7 or g++-7 or even -std=c++17 so i had to install g++-6 and gcc-6 using apt-get install anyway, after installing the 6 version the compiler include c++17. i'm using codeblocks as IDE, i had to add a new compiler and add the option -std=c++17 to enable it,but in the main code when i include the filesystem library it says no such file or directory.

my question is, how i can add the c++17 compiler and its library (like filesystem) correctly ??

Just because the switch says "C++17" doesn't mean that it implements all of C++17. — Nicol Bolas
– Nicol Bolas, Commented Aug 24, 2017 at 17:10
More specifically, it can only implement the language parts. The library parts are outside the compiler's purview. — Ignacio Vazquez-Abrams
– Ignacio Vazquez-Abrams, Commented Aug 24, 2017 at 17:12
@IgnacioVazquez-Abrams: Well, the compiler switches are also used to activate the library parts, since they're included with the compiler in the distro. But you're right that libstdc++ is updated separately from gcc. — Nicol Bolas
– Nicol Bolas, Commented Aug 24, 2017 at 17:15
@Nicol It's not updated seperately at all: specific GCC releases are quite tightly bound to specific libstdc++ snapshots. The version numbering works slightly different and both are developed semi-independently (as language feature implementation in the compiler permits). — rubenvb
– rubenvb, Commented Aug 22, 2018 at 14:28
@Rick you'll probably have two even though the newer one should work as a drop-in replacement for the old one. — rubenvb
– rubenvb, Commented Nov 27, 2018 at 15:44

Galik · Accepted Answer · 2018-08-22 14:25:02Z

75

GCC v7 still does not implement <filesystem> but it does have the Filesystem Technical Specification which is in <experimental/filesystem>

#include <experimental/filesystem>

// for brevity
namespace fs = std::experimental::filesystem;

int main()
{
    fs::path p = "/path/to/my/file"; // etc...
}

This is also available in GCC v6.

To link with the library you need to add -lstdc++fs to the command line.

Note: There may be some minor differences between the current Technical Specification and the final draft of <filesystem> that is decided upon by the Standards Committee.

Note 2: GCC v8 now implements <filesystem> with the -std=c++17 flag.

edited Aug 22, 2018 at 14:25

answered Aug 24, 2017 at 17:15

Galik

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Jonathan Wakely · Accepted Answer · 2024-03-25 10:20:19Z

First you should take at look at C++17 Support in GCC

GCC 8

Runtime Library (libstdc++)

Improved experimental support for C++17, including the following features:

Deduction guides to support class template argument deduction.

std::filesystem implementation.

std::char_traits<char> and std::char_traits<wchar_t> are usable in constant expressions.

std::to_chars and std::from_chars (for integers only, not for floating point types).

src: https://gcc.gnu.org/gcc-8/changes.html#libstdcxx

GCC 9

Runtime Library (libstdc++)

Improved support for C++17, including:

The C++17 implementation is no longer experimental.

Parallel algorithms and <execution> (requires Thread Building Blocks 2018 or newer).

<memory_resource>.

Using the types and functions in <filesystem> does not require linking with -lstdc++fs now.

src: https://gcc.gnu.org/gcc-9/changes.html#libstdcxx

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