How to read in a directory of files - c++

Question

I am writing a program in C++ which is going to process a large number (thousands) of PPM images all stored in the same directory. However, I first need to read in the pixel values. Is their a built in function in the standard namespace or a library I could import that would allow me to read in all the files one at a time without assuming I already know the file name using some sort of loop structure? In case it makes a difference I am writing the program on a Mac.

Answer 1

In order to avoid including boost::filesystem and the required dependencies, I ended up implementing this function:
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <stdexcept>
//include headers required for directory traversal
#if defined(_WIN32)
//disable useless stuff before adding windows.h
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#else
#include "dirent.h"
#endif
/**
Traverses the provided directory (non-recursively) and extracts the absolute paths to all the files in it.
Doesn't support non-ASCII file names.
#param directory the absolute path to the directory
#return a vector of file names (including extension)
*/
std::vector<std::string> Filesystem::GetFilesInDirectory(const std::string &directory)
{
std::vector<std::string> output;
#if defined(_WIN32)
//select all files
std::string tempDirectory = directory + "*";
//initialize the WIN32_FIND_DATA structure
WIN32_FIND_DATA directoryHandle = {0};
//set the directory
std::wstring wideString = std::wstring(tempDirectory.begin(), tempDirectory.end());
LPCWSTR directoryPath = wideString.c_str();
//iterate over all files
HANDLE handle = FindFirstFile(directoryPath, &directoryHandle);
while(INVALID_HANDLE_VALUE != handle)
{
//skip non-files
if (!(directoryHandle.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY))
{
//convert from WCHAR to std::string
size_t size = wcslen(directoryHandle.cFileName);
std::vector<char> buffer;
buffer.resize(2 * size + 2);
size_t convertedCharacters = 0;
wcstombs_s(&convertedCharacters, buffer.data(), 2 * size + 2, directoryHandle.cFileName, _TRUNCATE);
//trim the null characters (ASCII characters won't fill the vector, since they require fewer bytes)
//convertedCharacters includes the null character, which we want to discard
std::string file(buffer.begin(), buffer.begin() + convertedCharacters - 1);
//add the absolute file path
output.emplace_back(file);
}
if(false == FindNextFile(handle, &directoryHandle)) break;
}
//close the handle
FindClose(handle);
#else
DIR *directoryHandle = opendir(directory.c_str());
if (NULL != directoryHandle)
{
dirent *entry = readdir(directoryHandle);
while (NULL != entry)
{
//skip directories and select only files (hopefully)
//if ((DT_DIR != entry->d_type) && (DT_UNKNOWN == entry->d_type))
if (DT_REG == entry->d_type)
{
output.emplace_back(entry->d_name);
}
//go to next entry
entry = readdir(directoryHandle);
}
closedir(directoryHandle);
}
#endif
return output;
}
I'm not very proud of the above unflexible / mostly useless / platform dependent code and I would definitely go for BOOST if possible. By the way, it's not tested on a MAC, so please let me know if it does the trick.