C++ programs showing boost::filesystem usage contrasted with std::filesystem. Output of each program included to highlight differences/similarities.

diff_boost_std_mains.patch

$ diff main_boostfs.cpp main_stdfs.cpp
2c2
<     File:    main_boostfs.cpp
---
>     File:    main_stdfs.cpp
5,6c5,6
<     Purpose: Program to demonstrate aspects of boost::filesystem
<     NOTE:    Contrast behaviour differences with output of main_stdfs.cpp
---
>     Purpose: Program to demonstrate aspects of std::filesystem
>     NOTE:    Contrast behaviour differences with output of main_boostfs.cpp
8,11c8,10
<         [clang++|g++] [-I<path to boost include folder>] \
<                       [-L<path to boost libs>] \
<                       main_boostfs.cpp -o testboost \
<                       -l boost_system -l boost_filesystem
---
>         [clang++|g++] -std=c++17 \
>                       main_stdfs.cpp -o teststdfs \
>                       -lstdc++fs
16a16
> #include <filesystem>
18,23c18
< #ifndef BOOST_FILESYSTEM_NO_DEPRECATED
< #define BOOST_FILESYSTEM_NO_DEPRECATED
< #endif
< #include <boost/filesystem.hpp>
< 
< namespace fs = boost::filesystem;
---
> namespace fs = std::filesystem;
58a54
>         // NOTE: std::filesystem does not have reverse path iterators!!!
62c58
<         for( auto it = decompPath.rbegin(); it != decompPath.rend(); ++it )
---
>         for( auto it = decompPath.end(); it != decompPath.begin(); )
63a60
>             --it;

main_boostfs.cpp

/*
    File:    main_boostfs.cpp
    Date:    2019Apr26
    Author:  Scott Furry
    Purpose: Program to demonstrate aspects of boost::filesystem
    NOTE:    Contrast behaviour differences with output of main_stdfs.cpp
    Compile:
        [clang++|g++] [-I<path to boost include folder>] \
                      [-L<path to boost libs>] \
                      main_boostfs.cpp -o testboost \
                      -l boost_system -l boost_filesystem
*/
#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>

#ifndef BOOST_FILESYSTEM_NO_DEPRECATED
#define BOOST_FILESYSTEM_NO_DEPRECATED
#endif
#include <boost/filesystem.hpp>

namespace fs = boost::filesystem;
using namespace std;

int main(int argc, char* argv[])
{
    if( argc != 2 )
    {
        cout << "Missing Path! Usage: " << argv[0] << " [valid file path]" << endl;
        return 1;
    }
    
    try
    {
        fs::path testpath( fs::canonical( argv[1] ));
        cout << "User provided absolute path: "
             << (fs::path(argv[1]).is_absolute() ? "True" : "False")
             << endl;
        // validate path supplied by user
        if( !fs::exists( testpath ))
        {
            cout << "Bad Path! Usage: " << argv[0] << " [valid file path]" << endl;
            return 1;            
        }
        
        // demonstrate by example necessity of fs::path with/without string()
        // stream << fs::path --> produces "path in quotes"
        // stream << fs::path::string() -> produces path not in quotes
        cout << "Current working dir:" << setw(3) << ' ' << fs::current_path() << endl;
        cout << "Current path seperator: " << fs::path::preferred_separator << endl;
        // print out some details about this path
        cout << "Root Path:" << setw(14) << ' ' << testpath.root_path().string() << endl;
        cout << "Parent Path:" << setw(12) << ' ' << testpath.parent_path().string() << endl;

        // iterate backwards through path for decomposition
        // use output to build path - in reverse
        // need to create a derived path to use filesystem path iterators
        fs::path revPath;
        fs::path decompPath( testpath.parent_path() );
        cout << "Decomposition: " << endl;
        for( auto it = decompPath.rbegin(); it != decompPath.rend(); ++it )
        {
            // (*it) is type fs::path
            cout << setw(6) << ' ' << (*it).string() << endl;
            // path append operator - separator added by library
            revPath /= (*it);
        }
        // NOTE: output std::filesystem will be different from boost::filesystem
        // problem is with append operator where appending path that starts with "/"
        cout << "Reverse Path:" << setw(11) << ' ' << revPath.string() << endl;

        // Dig into information about path supplied by the user
        cout << "Path Filename:" << setw(10) << ' ' << testpath.filename().string() << endl;
        if( fs::is_regular_file( testpath ))
        {
            // user gave a file name - print some more details
            cout << testpath.string() << " size is " << fs::file_size(testpath) << " bytes" << endl;
            cout << setw(6) << ' ' << "File Name Stem: " << testpath.stem().string() << endl;
            cout << setw(6) << ' ' << "File Extension: " << testpath.extension().string() << endl;
        }
        else if( fs::is_directory( testpath ))
        {
            cout << testpath.string() << " is a directory containing:" << endl;
            typedef vector<fs::path> vec;   // store paths,
            vec vPaths;                     // so we can sort them later
            // STL algorithm magic to save path all at once
            copy( fs::recursive_directory_iterator( testpath ),
                  fs::recursive_directory_iterator(),
                  back_inserter( vPaths ));
            // sort names of directory contents - not done by filesystem
            // explicitly call out using sort from std namespace
            std::sort( vPaths.begin(), vPaths.end() );
            for( auto& aPath : vPaths )
            {
                cout << setw(6) << ' ' << aPath.string() << '\n';
            }
        }
        else
        {
            cout << testpath << " exists, but is neither a regular file nor a directory" << endl;
        }

    }
    catch (const fs::filesystem_error& ex)
    {
        cout << ex.what() << '\n';
    }
    return 0;
}

main_stdfs.cpp

/*
    File:    main_stdfs.cpp
    Date:    2019Apr26
    Author:  Scott Furry
    Purpose: Program to demonstrate aspects of std::filesystem
    NOTE:    Contrast behaviour differences with output of main_boostfs.cpp
    Compile:
        [clang++|g++] -std=c++17 \
                      main_stdfs.cpp -o teststdfs \
                      -lstdc++fs
*/
#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <filesystem>

namespace fs = std::filesystem;
using namespace std;

int main(int argc, char* argv[])
{
    if( argc != 2 )
    {
        cout << "Missing Path! Usage: " << argv[0] << " [valid file path]" << endl;
        return 1;
    }
    
    try
    {
        fs::path testpath( fs::canonical( argv[1] ));
        cout << "User provided absolute path: "
             << (fs::path(argv[1]).is_absolute() ? "True" : "False")
             << endl;
        // validate path supplied by user
        if( !fs::exists( testpath ))
        {
            cout << "Bad Path! Usage: " << argv[0] << " [valid file path]" << endl;
            return 1;            
        }
        
        // demonstrate by example necessity of fs::path with/without string()
        // stream << fs::path --> produces "path in quotes"
        // stream << fs::path::string() -> produces path not in quotes
        cout << "Current working dir:" << setw(3) << ' ' << fs::current_path() << endl;
        cout << "Current path seperator: " << fs::path::preferred_separator << endl;
        // print out some details about this path
        cout << "Root Path:" << setw(14) << ' ' << testpath.root_path().string() << endl;
        cout << "Parent Path:" << setw(12) << ' ' << testpath.parent_path().string() << endl;

        // iterate backwards through path for decomposition
        // use output to build path - in reverse
        // need to create a derived path to use filesystem path iterators
        // NOTE: std::filesystem does not have reverse path iterators!!!
        fs::path revPath;
        fs::path decompPath( testpath.parent_path() );
        cout << "Decomposition: " << endl;
        for( auto it = decompPath.end(); it != decompPath.begin(); )
        {
            --it;
            // (*it) is type fs::path
            cout << setw(6) << ' ' << (*it).string() << endl;
            // path append operator - separator added by library
            revPath /= (*it);
        }
        // NOTE: output std::filesystem will be different from boost::filesystem
        // problem is with append operator where appending path that starts with "/"
        cout << "Reverse Path:" << setw(11) << ' ' << revPath.string() << endl;

        // Dig into information about path supplied by the user
        cout << "Path Filename:" << setw(10) << ' ' << testpath.filename().string() << endl;
        if( fs::is_regular_file( testpath ))
        {
            // user gave a file name - print some more details
            cout << testpath.string() << " size is " << fs::file_size(testpath) << " bytes" << endl;
            cout << setw(6) << ' ' << "File Name Stem: " << testpath.stem().string() << endl;
            cout << setw(6) << ' ' << "File Extension: " << testpath.extension().string() << endl;
        }
        else if( fs::is_directory( testpath ))
        {
            cout << testpath.string() << " is a directory containing:" << endl;
            typedef vector<fs::path> vec;   // store paths,
            vec vPaths;                     // so we can sort them later
            // STL algorithm magic to save path all at once
            copy( fs::recursive_directory_iterator( testpath ),
                  fs::recursive_directory_iterator(),
                  back_inserter( vPaths ));
            // sort names of directory contents - not done by filesystem
            // explicitly call out using sort from std namespace
            std::sort( vPaths.begin(), vPaths.end() );
            for( auto& aPath : vPaths )
            {
                cout << setw(6) << ' ' << aPath.string() << '\n';
            }
        }
        else
        {
            cout << testpath << " exists, but is neither a regular file nor a directory" << endl;
        }

    }
    catch (const fs::filesystem_error& ex)
    {
        cout << ex.what() << '\n';
    }
    return 0;
}

output_testboostfs.txt

## with directory name provided
$ ./testboostfs .
User provided absolute path: False
Current working dir:   "/home/user/topic/guest_articles"
Current path seperator: /
Root Path:              /
Parent Path:            /home/user/topic
Decomposition: 
      topic
      user
      home
      /
Reverse Path:           topic/user/home/
Path Filename:          guest_articles
/home/user/topic/guest_articles is a directory containing:
      /home/user/topic/guest_articles/converting_from_boost_to_std_filesystem.md
      /home/user/topic/guest_articles/main_boostfs.cpp
      /home/user/topic/guest_articles/main_stdfs.cpp
      /home/user/topic/guest_articles/testboostfs
      /home/user/topic/guest_articles/teststdfs

## with file name provided
$ ./testboostfs main_boostfs.cpp
...
Parent Path:            /home/user/topic/guest_articles
Decomposition: 
      guest_articles
      topic
      user
      home
      /
Reverse Path:           guest_articles/topic/user/home/
Path Filename:          main_boostfs.cpp
/home/user/topic/guest_articles/main_boostfs.cpp size is 4402 bytes
      File Name Stem: main_boostfs
      File Extension: .cpp

output_teststdfs.txt

## with directory name provided
$ ./testboostfs .
User provided absolute path: False
Current working dir:   "/home/user/topic/guest_articles"
Current path seperator: /
Root Path:              /
Parent Path:            /home/user/topic
Decomposition: 
      topic
      user
      home
      /
Reverse Path:           /
Path Filename:          guest_articles
/home/user/topic/guest_articles is a directory containing:
      /home/user/topic/guest_articles/converting_from_boost_to_std_filesystem.md
      /home/user/topic/guest_articles/main_boostfs.cpp
      /home/user/topic/guest_articles/main_stdfs.cpp
      /home/user/topic/guest_articles/testboostfs
      /home/user/topic/guest_articles/teststdfs

## with file name provided
$ ./testboostfs main_boostfs.cpp
...
Parent Path:            /home/user/topic/guest_articles
Decomposition: 
      guest_articles
      topic
      user
      home
      /
Reverse Path:           /
Path Filename:          main_stdfs.cpp
/home/user/topic/guest_articles/main_stdfs.cpp size is 4300 bytes
      File Name Stem: main_stdfs
      File Extension: .cpp