The os.path equivalent in C++ without Qt?

Question

I need to set a directory and then read all the filenames of the files inside and store the whole path in a variable. I need to use this this variable later , to open the file and read it. I don't want use QDir for this. I saw the second answer to the question here. I can use boost/filesystem.hpp (I believe this need not be downloaded separately). But the problem is execution will look like this:

$ g++ -o test test.cpp -lboost_filesystem -lboost_system
$ ./test

My first line, for creating executable object is already complicated due to OpenCV libraries and I don't want to add to it. I want to keep them simple (the following line plus whatever OpenCV wants):

g++ -o test test.cpp

Is there any way to do it?

This is the python code for which I want to write C++ code:

root_dir = 'abc'
img_dir = os.path.join(root_dir,'subimages')

img_files = os.listdir(img_dir)
for files in img_files:
    img_name = os.path.join (img_dir,files)
    img = cv2.imread(img_name)

Avoid naming `test` your executable. It is a standard POSIX program `/bin/test` or a shell builtin. Call your test binary `mytest` — Basile Starynkevitch, Nov 01 '16 at 20:12
@BasileStarynkevitch I copied `test` from the other question, in the link. I just continued to use it for the rest of the question. — skr, Nov 01 '16 at 23:35
@Miki Thank you for the suggestion. Looks like I might be able get my job done with that. — skr, Nov 01 '16 at 23:36

score 3 · Accepted Answer · answered Nov 01 '16 at 18:56

3

Your choices are to use boost, QDir, roll your own, or use a newer compiler which has adopted some of the TR2 features that are staged for C++17. Below is a sample which roughly should iterate over files in a system agnostic manner with the C++17 feature.

#include <filesystem>
namespace fs = std::experimental::filesystem;
...
fs::directory_iterator end_iter;
fs::path subdir = fs::dir("abc") / fs::dir("subimages");
std::vector<std::string> files;

for (fs::directory_iterator dir_iter(subdir); dir_iter != end_iter; dir_iter++) {
  if (fs::is_regular_file(dir_iter->status())) {
    files.insert(*dir_iter);
  }
}

answered Nov 01 '16 at 18:56

Pyrce

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I think I will go with boost and create a file that contains everything that should be called while creating the object. What do you think of that? – skr Nov 01 '16 at 19:03
Sounds like the most reliable approach. In a few years there will be less need to carry such a large bundle into small problems like this. – Pyrce Nov 01 '16 at 20:00

score 1 · Answer 2 · answered Nov 01 '16 at 20:09

For Linux or POSIX ....

You might use low-level nftw(3) or opendir(3) & readdir(3) etc... Of course you'll need to deal with dirty details (skipping . & .. entries, assembling the file path from the entry and the directory path, handling errors, etc...). You might also need stat(2). You should read Advanced Linux Programming & syscalls(2) to get a broader view.

For other OSes (notably Windows) you need other low-level functions.

BTW, you could look into the source code of Qt for QDir

You could consider also using POCO

The os.path equivalent in C++ without Qt?

2 Answers2