Question

in header file I have defined the following function

#ifndef OS_H
#define OS_H

#include <string>
#include <vector>

int GetDirectoryFiles(std::string directory, std::vector<std::string> &files);

#endif /* OS_H */

I would like have separate implementations for each platform

#include "os.h"
#include <iostream>

#ifdef OSWIN
#include <windows.h>
#elif OSLINUX
#include <dirent.h>
#endif

int GetDirectoryFiles(std::string directory, std::vector<std::string> &files)
#ifdef OSLINUX
{
    DIR *dp;
    struct dirent *dirp;
    if((dp  = opendir(dir.c_str())) == NULL) {
        cout << "Error(" << errno << ") opening " << dir << endl;
        return errno;
    }

    while ((dirp = readdir(dp)) != NULL) {
        files.push_back(string(dirp->d_name));
    }
    closedir(dp);
    return 0;
}
#elif OSWIN
{
    std::clog << "entered!" << std::endl;

    WIN32_FIND_DATA FindFileData;
    HANDLE hFind = FindFirstFile(directory.c_str(), &FindFileData);
    if ( hFind == INVALID_HANDLE_VALUE )
        return -1;

    do {
        files.push_back(FindFileData.cFileName);
    } while(FindNextFile(hFind, &FindFileData) != 0);
    FindClose( hFind );

    return 0;
}
#endif

Is there more elegant way to do this (what is considered good style).

Answer 1

The typical way to handle this would be to have the function declaration in a shared header file, then have one cpp file per platform that contains the different platform-specific definitions of this function. Your build system then only makes and links in the corresponding platform-specific cpp file.

ie

Filesystem.h

#include <string>
#include <vector>

int GetDirectoryFiles(std::string directory, std::vector<std::string> &files);

Filesystem_Windows.cpp:

#include "Filesystem.h"

int GetDirectoryFiles(std::string directory, std::vector<std::string> &files);
{
    WIN32_FIND_DATA FindFileData;
    HANDLE hFind = FindFirstFile(directory.c_str(), &FindFileData);
    ...    
    return 0;
}

Filesystem_Linux.cpp:

#include "Filesystem.h"

int GetDirectoryFiles(std::string directory, std::vector<std::string> &files);
{
    DIR *dp;
    struct dirent *dirp;
    ...
    return 0;

}

See the source tree of Qt, which is a very popular cross-platform C++ library, as an example of this kind of structure.