How to read files from a directory in c++ in a platform independent way?

Question

I have an assignment that require me to develop a program that is passed either a file name or a directory name.

if what is passed is a directory name then i have to read all the files in that directory and basically do some processing on them.

the problem is that I am using c++ and c++ out of the box doesn't really play nice with file systems without third party/system libs.

how can I read all the files from a directory without platform dependency because I am using a windows machine and the grader is using linux machine.

I tried to use filesystem and I have gcc 9.2 but it doesn't compile

it doesn't compile this file:

#include <iostream> 
#include <filesystem>

namespace fs = std::filesystem;

int main(){
    
    fs::path p("some-path");
 
}

it results in this compiler error:

testfs.cpp:4:21: error: 'filesystem' is not a namespace-name
    4 | namespace fs = std::filesystem;
      |                     ^~~~~~~~~~
testfs.cpp: In function 'int main()':
testfs.cpp:8:5: error: 'fs' has not been declared
    8 |     fs::path p("some-path");

GCC 9.2 doesn't default to compiling to the c++17 standard revision, the first to support filesystem. Force it by adding `-std=c++17` to the command line. Examples with and without : https://godbolt.org/z/Tj6car — user4581301, Sep 05 '20 at 00:10
I'm utterly flabbergasted that I can't find a decent duplicate for this. — user4581301, Sep 05 '20 at 00:17
"c++ out of the box doesn't really play nice with file systems" Your compiler error aside (which isnt "c++ playing with the filesystem") it is not clear what general problem you refer to — 463035818_is_not_an_ai, Sep 05 '20 at 00:20
@user4581301 same question but different gcc version and flags: https://stackoverflow.com/questions/48312460/c17-filesystem-is-not-a-namespace-name — 463035818_is_not_an_ai, Sep 05 '20 at 00:22
Saw that one. The killer there was more the GCC version predates the C++17 release/ — user4581301, Sep 05 '20 at 00:23
does this answer your question? https://stackoverflow.com/questions/46980383/how-to-determine-what-c-standard-is-the-default-for-a-c-compiler/46980534 — 463035818_is_not_an_ai, Sep 05 '20 at 00:25
Don't forget to input library name `stdc++fs` if you're using `gcc`. — John Park, Sep 05 '20 at 03:39
it worked after I added -std=c++17, g++ didn't compile to c++17 by default indeed — Xenouth, Sep 05 '20 at 12:09

user4581301 · Answer 1 · 2020-09-05T00:31:47.283

filesystem::path is by far the best cross-platform solution for platforms with a compiler that supports C++17, the first to support filesystem, or a newer Standard revision.

GCC 9.2 doesn't default to compiling to the c++17 standard revision.

Force C++ 17 support by adding -std=c++17 to the command line, selecting the C++17 dialect in your IDE's Compiler option property pages, or editing the appropriate configuration file to add the option.

Examples with and without the extra compiler option: https://godbolt.org/z/Tj6car

If a C++17 or newer compiler is not available on your system, consider using boost::filesystem

it worked after I added -std=c++17, g++ didn't compile to c++17 by default indeed — Xenouth, Sep 05 '20 at 12:10

How to read files from a directory in c++ in a platform independent way?

1 Answers1