recursion - Recursive directory copying in C

Question

I am very new to C programming and there is little helpful information anywhere on how to do recursive copying of the contents of a directory in C (not C++,C#, Objective-C, Java, shell, Python, or anything else--this MUST be done in C). Yes, this is homework and it is due tomorrow night, and I have been stuck for almost two weeks trying to get this done.

I am trying to search for any backup versions of a given directory (e.g. a directory "dir" with a backup directory "/dir.bak"). If there is not, create that "/dir.bak" directory, or if there is, create a backup directory named "/dir.bak.MM-DD-YY-HH-MM-SS" instead. Then copy everything from the source directory into the destination directory.

When I attempt to run this code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <dirent.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/time.h>
#include <time.h>

#define BUFSIZE 256

int main (int argc, char* argv[])
{
    DIR *dir;
    struct dirent *dentry;
    struct stat statbuff;
    char buffer[BUFSIZE];//holds time and date suffix
    ssize_t count;
    int fdin, fdout;    
    mode_t  perms =  740;//perms for file I/O ops
    char *cwdNamePntr;
    long maxpath;
    if ( argc != 3 ) //if incorrect number of args passed in...
    {
        printf( "Usage: %s Directory-Path-Name Destination-Folder
 ", argv[0] );
        exit(1);
    }
    char  buffer2[BUFSIZE];//buffer for file I/O ops
    char* datetime;
    int retval;
    time_t  clocktime;
    struct tm  *timeinfo;
    time (&clocktime);
    timeinfo = localtime( &clocktime );
    strftime(buffer, BUFSIZE, "%b-%d-%Y-%H-%M-%S", timeinfo);//store time and date suffix in case we need it
    chdir(argv[1]);
    char *path = argv[2];//source path for I/O ops
    char *newpath = malloc(strlen(path) + 26);//destination paths for I/O ops
    strcpy(newpath,path);
    strcat(newpath,".bak");//test name for backup directory
    if(chdir(newpath)==0)
    {//if our test name is already a directory
        chdir("..");
        strcat(newpath,".");
        strcat(newpath,buffer);//add time and date suffix onto the name of new backup directory
    }
    if ( (mkdir(newpath, perms)) == 0 )//if we successfully made a new backup directory
    {
        chdir(path);
        dir = opendir(".");//move into source directory
        if ( dir ==  0 )
        {//if open directory fails
                fprintf (stderr, "Error in opening directory:  %s
", path );
            perror( "Could not open directory");
                exit(2);
        }
        dentry = readdir (dir);//load directory

        while (dentry != 0)//while we are reading a directory
        {
            char *filename = dentry->d_name;//get name of file to be copied
            if( (strcmp(filename,".")!=0) && (strcmp(filename,"..")!=0) )
            {
                if  ( (fdin = open ( filename,  O_RDONLY))  == -1)
                {//if cannot open input file
                        perror ( "Error in opening the input file:");
                        exit (2);
                }
                chdir("..");//go back to parent directory
                chdir(newpath);//move to destination directory
                opendir(".");
                if  ( (fdout = open (filename, (O_WRONLY | O_CREAT), perms)) == -1 )
                {//if cannot create output file...
                        perror ( "Error in creating the output file:");
                        exit (3);
                }
                while ( (count=read(fdin, buffer2, BUFSIZE)) > 0 )
                {
                        if ( write (fdout, buffer2, count) != count )
                    {//if cannot write   
                                perror ("Error in writing" );
                                exit(3);
                        }
                } 

                    if ( count == -1 )
                    {//if cannot read
                        perror ( "Error while reading the input file: ");
                        exit(4);
                }

                close(fdin);
                close(fdout);
            }
            chdir("..");//back to parent directory again
            dir = opendir(".");
            if ( dir ==  0 )//if open directory fails
            {
                    fprintf (stderr, "Error in opening directory:  %s
", path );
                perror( "Could not open directory");
                    exit(666);
            }
            dentry = readdir (dir);//reload directory
        }
    }
    else
    {
        perror("Error in directory creation");
        exit(2);
    }
    return 0;  
}

I get THIS error:

[my-desktop]@ubuntu:~/Desktop$ ./helpmehelpyou.out ~/Desktop new
Error in creating the output file:: Permission denied

A bunch of this code was taken from sample files which our instructors said we could use. I don't understand why this is not working right? The finished function must be recursive and is part of a four-choice program with this being option 4. C is very hard for me to grasp or understand, and like I said, there is very little information about this stuff for C, but an overabundance of it for C#, C++, Objective C, and every other language. And like I also said, we MAY NOT use shell commands or anything else for this assignment.

Can someone please help me? Thanks!

Answer 1

This won't solve your problem, but I spotted a possible error in your code. I don't see the recursion happening.

You see, this code may work fine if you only have one subfolder. But what do you do, if there's a subfolder in that subfolder?

You need a recursive directory search function. This may look like this:

void SearchDirectory(const char *name) {
    DIR *dir = opendir(name);                //Assuming absolute pathname here.
    if(dir) {
        char Path[256], *EndPtr = Path;
        struct dirent *e;
        strcpy(Path, name);                  //Copies the current path to the 'Path' variable.
        EndPtr += strlen(name);              //Moves the EndPtr to the ending position.
        while((e = readdir(dir)) != NULL) {  //Iterates through the entire directory.
            struct stat info;                //Helps us know about stuff
            strcpy(EndPtr, e->d_name);       //Copies the current filename to the end of the path, overwriting it with each loop.
            if(!stat(Path, &info)) {         //stat returns zero on success.
                if(S_ISDIR(info.st_mode)) {  //Are we dealing with a directory?
                    //Make corresponding directory in the target folder here.
                    SearchDirectory(Path);   //Calls this function AGAIN, this time with the sub-name.
                } else if(S_ISREG(info.st_mode) { //Or did we find a regular file?
                    //Run Copy routine
                }
            }
        }
    }
}

This code will call the function SearchDirectory for as many times as there are subdirectories in the current folder. If the architecture runs too deep you may run out of memory and the program may crash, so please beware.

Once it cannot find any more directories in the folder (it has reached the 'leaf'-folders), it will iterate over the remaining files and then end the function, popping the last function call from the stack, allowing the previous call to SearchDirectory to continue searching.

After all is said and done, you'll have a full recursive copy.

P.S: Sorry for the spoiler, I read your comment only after I was done typing.