How can I copy a file from one directory to another in c/c++

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闹比i 2020-12-17 07:18

I am looking for a simple example on how to copy a file from one directory to another in C. The program should only use cross platform functions that are native to C.

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陌清茗 (楼主)

2020-12-17 08:02

The correct way to copy files in C++ using dirent.h is below. Note that dirent.h is part of Linux but not included in Windows. For Windows look here.

For Windows Visual C++:

 // CopyAll_Windows.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include
#include"dirent.h"   //Copy dirent.h to folder where stdafx.h is and add to project
#include
#include
#include 

#define MAX 1024
#define MAX_FILE_NAME_LEN 256

using namespace std;

int main()
{
    string homedir = "C:\\Users\\Tom\\Documents";
    cerr << endl << "Home =  " << homedir.c_str() << endl;
    string SrcPath = homedir + "\\Source 1";
    string DestPath = homedir + "\\Dest 1\\Dest 1";
    string DestPath_mkdir = "\"" + DestPath + "\"";
    string command = "mkdir " + DestPath_mkdir;
    cerr << endl << "Command = " << command.c_str() << endl << endl;
    system(command.c_str());
    const char *arSrcPath = SrcPath.c_str();
    const char *arDestPath = DestPath.c_str();

    struct dirent* spnDirPtr;    /* struct dirent to store all files*/
    DIR* pnWriteDir = NULL;    /*DIR Pointer to open Dir*/
    pnWriteDir = opendir(arDestPath);

    if (!pnWriteDir)
        cerr << endl << "ERROR! Write Directory can not be open" << endl;

    DIR* pnReadDir = NULL;    /*DIR Pointer to open Dir*/
    pnReadDir = opendir(arSrcPath);

    if (!pnReadDir || !pnWriteDir)
        cerr << endl << "ERROR! Read or Write Directory can not be open" << endl << endl;

    else
    {
        int nErrNo = 0;

        while ((spnDirPtr = readdir(pnReadDir)) != NULL)
        {
            char readPath[MAX_FILE_NAME_LEN] = { 0 };
            memset(readPath, 0, MAX_FILE_NAME_LEN);

            // Following line needed to get real path for "stat" call
            _snprintf_s(readPath, MAX_FILE_NAME_LEN, _TRUNCATE, "%s/%s", arSrcPath, spnDirPtr->d_name);
            struct stat st_buf;
            stat(readPath, &st_buf);

            if (S_ISDIR(st_buf.st_mode))
            {
                cerr << endl << "Reading directory here..." << endl;
                continue;
            }
            else if (S_ISREG(st_buf.st_mode))
            {
                if (nErrNo == 0)
                    nErrNo = errno;

                cerr << endl << "Now reading and writing file " << spnDirPtr->d_name << endl;
                char strSrcFileName[MAX_FILE_NAME_LEN] = { 0 };
                memset(strSrcFileName, 0, MAX_FILE_NAME_LEN);

                // Following line needed to get real path for "pnReadFile"
                _snprintf_s(strSrcFileName, MAX_FILE_NAME_LEN, _TRUNCATE, "%s/%s", arSrcPath, spnDirPtr->d_name);

                FILE* pnReadFile;
                errno_t err_read;

                if ((err_read = fopen_s(&pnReadFile, strSrcFileName, "r")) == 0)
                {
                    cerr << endl << "Now reading file " << strSrcFileName << endl;
                    char strDestFileName[MAX_FILE_NAME_LEN] = { 0 };
                    memset(strDestFileName, 0, MAX_FILE_NAME_LEN);

                    // Following line needed to get real path for "pnWriteFile"
                    _snprintf_s(strDestFileName, MAX_FILE_NAME_LEN, _TRUNCATE, "%s/%s", arDestPath, spnDirPtr->d_name);

                    FILE* pnWriteFile;  /*File Pointer to write in file*/
                    errno_t err_write;

                    if ((err_write = fopen_s(&pnWriteFile, strDestFileName, "w")) == 0)
                    {
                        cerr << endl << "Now writing file " << strDestFileName << endl;
                        char buffer[MAX] = { 0 };    /*Buffer to store files content*/

                        while (fgets(buffer, MAX, pnReadFile))
                        {
                            fputs(buffer, pnWriteFile);
                        }
                        fclose(pnWriteFile);
                    }
                    else
                    {
                        cerr << endl << "Error! Unable to open file for writing " << strDestFileName << endl;
                    }
                    fclose(pnReadFile);
                }
                else
                {
                    cerr << endl << "ERROR! File Could not be open for reading" << endl;
                }
            }
        }
        if (nErrNo != errno)
            cerr << endl << "ERROR Occurred!" << endl;
        else
            cerr << endl << "Process Completed" << endl << endl;
    }
    closedir(pnReadDir);
    closedir(pnWriteDir);

    return 0;
}

For Linux Eclipse C++:

// CopyAll_linux.cpp : Defines the entry point for the console application.
//

//#include "stdafx.h"
#include
#include
#include
#include
#include
#include
#include
#include 
#include 
#include 
#include 

#define MAX 1024
#define MAX_FILE_NAME_LEN 256

using namespace std;

int main()
{
    const char *homedir;
    if ((homedir = getenv("HOME")) == NULL) {
        homedir = getpwuid(getuid())->pw_dir;
    }
    cerr << endl << "Home =  " <<  homedir << endl;
    string hd(homedir);
    string SrcPath = hd + "/Source 1";
    string DestPath = hd + "/Dest 1/Dest 1";
    string DestPath_mkdir = "\"" + DestPath + "\"";
    string command = "mkdir -p " + DestPath_mkdir;
    cerr << endl << "Command = " <<  command.c_str() << endl << endl;
    system(command.c_str());
    const char *arSrcPath = SrcPath.c_str();
    const char *arDestPath = DestPath.c_str();

    struct dirent* spnDirPtr;    /* struct dirent to store all files*/
    DIR* pnWriteDir = NULL;    /*DIR Pointer to open Dir*/
    pnWriteDir = opendir(arDestPath);

    if (!pnWriteDir)
        cerr << endl << "ERROR! Write Directory can not be open" << endl;

    DIR* pnReadDir = NULL;    /*DIR Pointer to open Dir*/
    pnReadDir = opendir(arSrcPath);

    if (!pnReadDir || !pnWriteDir)
        cerr << endl <<"ERROR! Read or Write Directory can not be open" << endl << endl;

    else
    {
        int nErrNo = 0;

        while ((spnDirPtr = readdir(pnReadDir)) != NULL)
        {
            char readPath[MAX_FILE_NAME_LEN] = { 0 };
            memset(readPath, 0, MAX_FILE_NAME_LEN);
            // Following line needed to get real path for "stat" call
            snprintf(readPath, MAX_FILE_NAME_LEN, "%s/%s", arSrcPath, spnDirPtr->d_name);
            struct stat st_buf;
            stat(readPath, &st_buf);

            if (S_ISDIR(st_buf.st_mode))
            {
                cerr << endl << "Reading directory here..." << endl;
                continue;
            }
            else if (S_ISREG(st_buf.st_mode))
            {
                if (nErrNo == 0)
                    nErrNo = errno;

                cerr << endl << "Now reading and writing file "<< spnDirPtr->d_name << endl;
                char strSrcFileName[MAX_FILE_NAME_LEN] = { 0 };
                memset(strSrcFileName, 0, MAX_FILE_NAME_LEN);
                // Following line needed to get real path for "pnReadFile"
                snprintf(strSrcFileName, MAX_FILE_NAME_LEN, "%s/%s", arSrcPath, spnDirPtr->d_name);
                FILE* pnReadFile;
                pnReadFile = fopen(strSrcFileName, "r");

                if (pnReadFile == NULL)
                    cerr << endl << "Null pointer on read file ..." << endl;

                if (pnReadFile)
                {
                    cerr << endl << "Now reading file " << strSrcFileName << endl;
                    char strDestFileName[MAX_FILE_NAME_LEN] = { 0 };
                    memset(strDestFileName, 0, MAX_FILE_NAME_LEN);
                    // Following line needed to get real path for "pnWriteFile"
                    snprintf(strDestFileName, MAX_FILE_NAME_LEN, "%s/%s", arDestPath, spnDirPtr->d_name);
                    FILE* pnWriteFile = fopen(strDestFileName, "w");    /*File Pointer to write in file*/

                    if (pnWriteFile)
                    {
                        cerr << endl << "Now writing file " << strDestFileName << endl;
                        char buffer[MAX] = { 0 };    /*Buffer to store files content*/

                        while (fgets(buffer, MAX, pnReadFile))
                        {
                            fputs(buffer, pnWriteFile);
                        }
                        fclose(pnWriteFile);
                    }
                    else
                    {
                        cerr << endl << "Error! Unable to open file for writing " << strDestFileName << endl;
                    }
                    fclose(pnReadFile);
                }
                else
                {
                    cerr << endl << "ERROR! File Could not be open for reading" << endl;
                }
            }
        }
        if (nErrNo != errno)
            cerr << endl << "ERROR Occurred!" << endl;
        else
            cerr << endl << "Process Completed" << endl << endl;
    }
    closedir(pnReadDir);
    closedir(pnWriteDir);

    return 0;
}

Visual Studio C++ dll:

 // copy_all_dll.cpp : Defines the exported functions for the DLL application.
//

#include "stdafx.h"
#include
#include"dirent.h"   //Copy dirent.h to folder where stdafx.h is and add to project
#include
#include
#include 

#define MAX 1024
#define MAX_FILE_NAME_LEN 256

using namespace std;

BOOL DirectoryExists(const char* dirName);

extern "C"  __declspec(dllexport) char*  copy_combos_all(char *source, char *dest)

{
    char *pnError = "";

    BOOL dest_exists = DirectoryExists(dest);

    if (!dest_exists)
    {
        string DestPath(dest);
        DestPath = "\"" + DestPath + "\"";
        string command = "mkdir " + DestPath;
        system(command.c_str());
    }

    const char *arSrcPath = source;
    const char *arDestPath = dest;

    struct dirent* spnDirPtr;    /* struct dirent to store all files*/
    DIR* pnWriteDir = NULL;    /*DIR Pointer to open Dir*/
    pnWriteDir = opendir(arDestPath);
    if (!pnWriteDir)
    {
        pnError =  "ERROR! Write Directory can not be open";
        return pnError;
    }
    DIR* pnReadDir = NULL;    /*DIR Pointer to open Dir*/
    pnReadDir = opendir(arSrcPath);

    if (!pnReadDir) 
    {
        pnError = "ERROR! Read Directory can not be open";
        if (pnWriteDir)
        {
            closedir(pnWriteDir);
        }
        return pnError;
    }
    else
    {
        int nErrNo = 0;

        while ((spnDirPtr = readdir(pnReadDir)) != NULL)
        {
            char readPath[MAX_FILE_NAME_LEN] = { 0 };
            memset(readPath, 0, MAX_FILE_NAME_LEN);

            // Following line needed to get real path for "stat" call
            _snprintf_s(readPath, MAX_FILE_NAME_LEN, _TRUNCATE, "%s/%s", arSrcPath, spnDirPtr->d_name);
            struct stat st_buf;
            stat(readPath, &st_buf);

            if (S_ISDIR(st_buf.st_mode))
            {
                continue;
            }
            else if (S_ISREG(st_buf.st_mode))
            {
                if (nErrNo == 0)
                    nErrNo = errno;

                char strSrcFileName[MAX_FILE_NAME_LEN] = { 0 };
                memset(strSrcFileName, 0, MAX_FILE_NAME_LEN);

                // Following line needed to get real path for "pnReadFile"
                _snprintf_s(strSrcFileName, MAX_FILE_NAME_LEN, _TRUNCATE, "%s/%s", arSrcPath, spnDirPtr->d_name);

                FILE* pnReadFile;
                errno_t err_read;

                if ((err_read = fopen_s(&pnReadFile, strSrcFileName, "r")) == 0)
                {
                    char strDestFileName[MAX_FILE_NAME_LEN] = { 0 };
                    memset(strDestFileName, 0, MAX_FILE_NAME_LEN);

                    // Following line needed to get real path for "pnWriteFile"
                    _snprintf_s(strDestFileName, MAX_FILE_NAME_LEN, _TRUNCATE, "%s/%s", arDestPath, spnDirPtr->d_name);

                    FILE* pnWriteFile;
                    errno_t err_write;

                    if ((err_write = fopen_s(&pnWriteFile, strDestFileName, "w")) == 0)    /*File Pointer to write in file*/
                    {
                        char buffer[MAX] = { 0 };    /*Buffer to store files content*/

                        while (fgets(buffer, MAX, pnReadFile))
                        {
                            fputs(buffer, pnWriteFile);
                        }
                        fclose(pnWriteFile);
                    }
                    else
                    {
                        pnError = "Error! Unable to open file for writing ";
                        return pnError;
                    }
                    fclose(pnReadFile);
                }
                else
                {
                    pnError = "ERROR! File Could not be open for reading";
                    return pnError;
                }
            }
        }
        if (nErrNo != errno)
        {
            pnError = "ERROR Occurred!";
        }
        else
        {
            pnError = "Process Completed";
        }
    }
    if (pnReadDir)
    {
        closedir(pnReadDir);
    }
    if (pnWriteDir)
    {
        closedir(pnWriteDir);
    }

    return pnError;
}

BOOL DirectoryExists(const char* dirName) {
    DWORD attribs = ::GetFileAttributesA(dirName);
    if (attribs == INVALID_FILE_ATTRIBUTES) {
        return false;
    }
    return (attribs & FILE_ATTRIBUTE_DIRECTORY);
}

For the dll, you call call it as following:

VB.Net:


Public Shared Function copy_all(source As String, dest As String) As StringBuilder
End Function

Sub copyAll()

    Dim source, dest, homedir As String
    homedir = System.Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)
    source = homedir & "\Source"
    dest = homedir & "\Dest"

    If Not My.Computer.FileSystem.DirectoryExists(dest) Then
        My.Computer.FileSystem.CreateDirectory(dest)
    End If

    Dim errorMessage As String
    errorMessage = ""
    Dim sb As New StringBuilder()
    sb = copy_all(source, dest)
    errorMessage = sb.ToString

    If (errorMessage <> "") Then
        MessageBox.Show(errorMessage)
    End If


End Sub

Visual C#:

[DllImport("copy_all.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern IntPtr copy_all(string source, string dest);

public void copyAll()
{

    string homedir = System.Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
    string source = homedir + "\\Source";
    string dest = homedir + "\\Dest";
    string error = "";

    if (!Directory.Exists(dest))
        Directory.CreateDirectory(dest);

    IntPtr ptr = copy_all(source, dest);

    error = Marshal.PtrToStringAnsi(ptr);

    if (error != "")

        MessageBox.Show(error);

}

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