why does array return only last item?

cppcub (6)
Hi all,

I am new to this forum, and pretty new to C++. This is what I use:
WinXP Home SP2
mingw32: g++ (GCC) 3.4.2 (mingw-special)
Dev-C++ 4.9.9.2

My problem:
***********

*** 1 ***
I read 12 files of a directoy into a char *array. As control, I output each array item after having read each file. It looks ok, like this:

Array 0: .
Array 1: ..
Array 2: IMAG0004.JPG
Array 3: IMAG0005.JPG
Array 4: IMAG0006.JPG
Array 5: IMAG0007.JPG
Array 6: IMAG0010.JPG
Array 7: IMAG0011.JPG
Array 8: IMAG0012.JPG
Array 9: MPG_0001.MPG
Array 10: MPG_0002.MPG
Array 11: MPG_0003.MPG
Array 12: MPG_0008.MPG
Array 13: MPG_0009.MPG

*** 2 ***
If I iterate later in the program through the same array from i=0 to 12, the output is very strange, i.e., only the last directory entry is listed:

i: 0 Array 0: MPG_0009.MPG
i: 1 Array 1: MPG_0009.MPG
i: 2 Array 2: MPG_0009.MPG
i: 3 Array 3: MPG_0009.MPG
i: 4 Array 4: MPG_0009.MPG
i: 5 Array 5: MPG_0009.MPG
i: 6 Array 6: MPG_0009.MPG
i: 7 Array 7: MPG_0009.MPG
i: 8 Array 8: MPG_0009.MPG
i: 9 Array 9: MPG_0009.MPG
i: 10 Array 10: MPG_0009.MPG
i: 11 Array 11: MPG_0009.MPG
i: 12 Array 12: MPG_0009.MPG
i: 13 Array 13: MPG_0009.MPG

Can anybody help, please, what is wrong? Please find the program main.cpp at the end of my message.

Thank you,

cppcub

P.S. Now comes the listing. Note that this is only the beginning of larger program I am going to develop, to help me rename files from my digital camera. An note that I know that I should not use too many global variables and constants. Trust me, after this program will get to work, local variables and functions will folow suite.

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************************
main.cpp
************************
// reads files from subdirectory ./BB into array alleFiles[]
// 
// modified from :
// http://www.informit.com/guides/content.aspx?g=cplusplus&seqNum=245
// for details see end of program
// 2008-feb-20

#include <iostream>
#include <errno.h>
#include <dirent.h>
#include <stdio.h>
#include <stdlib.h>

const int directorySize = 20; // arbitrary size of array; currently less than 20 entries
char *alleFiles[directorySize];
int i = 0;

int main()
{
 for (i = 0; i < directorySize; i++)
     {
         alleFiles[i] = "string"; //to be on the safe side
     }
     
 DIR *pdir;
 struct dirent *pent;

 pdir=opendir("./BB"); // open directory
 if (!pdir){
 printf ("opendir() failure; terminating");
 exit(1);
 }
 errno=0;

 i = 0;
 
 //read directory ./BB and put entries into alleFiles[i]
 while ((pent=readdir(pdir))) 
 {
    //alleFiles[i] gets directory entries
	alleFiles[i] = pent->d_name; 
    std::cout << " Array " << i << ": " << alleFiles[i] << std::endl; //just to be sure it works
    i = i + 1;
    //alleFiles[5] = "fuenf"; // control: if this is outcommented, alleFiles[5] keeps the string "fuenf" 
 }
 if (errno)
 {
 printf ("readdir() failure; terminating");
 exit(1);
 }

 closedir(pdir);
 
 //check alleFiles[i] again
 for (i = 0; i < directorySize; i++)
 {
    std::cout << "i: " << i; 
    std::cout << " Array " << i << ": " << alleFiles[i]; // alleFiles[i] with i from 14, returns only last enty from ./BB! Why?
    std::cout << std::endl; // print alleFiles[i]
 } 
 
 std::cout << std::endl;
 system("PAUSE");
 return EXIT_SUCCESS;
}

/*
This is the source I modified main.cpp from. My major mdification was to 
add an array to hold all directory entries.

http://www.informit.com/guides/content.aspx?g=cplusplus&seqNum=245

Manipulating Directories

Last updated Jul 29, 2005.

Standard C++ doesn't have a library for manipulating directories. The closest 
thing you can get is Boost's filesystem library. However, most implementations 
nowadays support the quasi-standard <dirent.h> and <dir.h> libraries. These 
libraries, originally written in C, enable you to list the files in a directory, 
change the current directory, create a new directory and delete an existing 
directory.
Traversing a Directory

The <dirent.h> header declares functions for opening, reading, rewinding and 
closing a directory. To view the files in a directory, you have to open it first 
using the opendir() function:

DIR * opendir(const char * path);

opendir() returns a pointer to DIR. DIR is a data structure that represents a 
directory. A NULL return value indicates an error. path must be a name of an 
existing directory.

To traverse a successfully opened directory, use readdir():

struct dirent * readdir (DIR * pdir);

pdir is the pointer obtained from a previous opendir() call. readdir() returns 
a pointer to a dirent structure whose data member, d_name, contains the name of 
the current file (the rest of dirent's members depend on the specific file 
system installed on your machine so I won't discuss them here). Each successive 
call to readdir() advances to the next file in the directory.

readdir() returns NULL either in the event of an error or once you have 
traversed all the files in the directory. To distinguish between these two 
conditions, check errno after every readdir() call. Since readdir() changes 
errno only if an error has occurred, you need to reset it explicitly before each 
readdir() call.

The rewinddir() function resets a directory stream to the first entry:

void rewinddir(DIR *pdir);

rewinddir() also ensures that the directory accurately reflects any changes to 
the directory (file deletion, renaming etc.) since the last opendir() or 
rewinddir() calls.

Use closedir() to close the directory once you are done with it:

int closedir (DIR * pdir);

pdir is the pointer obtained from a previous opendir() call. 
*/
Last edited on
naja (18)
Well,
i compiled your code, and this is the output:

Array 0: file 4
Array 1: ..
Array 2: new file
Array 3: file 2
Array 4: file 3
Array 5: .


i: 0 Array 0: file 4
i: 1 Array 1: ..
i: 2 Array 2: new file
i: 3 Array 3: file 2
i: 4 Array 4: file 3
i: 5 Array 5: .
i: 6 Array 6: string
i: 7 Array 7: string
i: 8 Array 8: string
i: 9 Array 9: string
i: 10 Array 10: string
i: 11 Array 11: string
i: 12 Array 12: string
i: 13 Array 13: string
i: 14 Array 14: string
i: 15 Array 15: string
i: 16 Array 16: string
i: 17 Array 17: string
i: 18 Array 18: string
i: 19 Array 19: string


So according to my computer, your code works...
naja (18)
Oh,

by the way, i assume you are doing this to learn C++, because if you just want a practical solution for renaming your files from your camera, learn python. You wont regret it. It is much more suitable for small apps like this. You would probably have had a GUI and a full feature set by now in python... (its less low level and error prone, and you dont need to compile to test.)

good luck
cppcub (6)
if anybody is interested, here is the solution:

http://www.cplusplus.com/forum/general/459/
cppcub (6)
@naja

yes, I am learning C++. And since I did this renaming with Delphi before, I wonder whether one can do it with C++/Qt4, too. By the way, I have some experience with Python, e.g. with a program that reads my emails aloud to me. But I hate that I need a running Python to this end; and compiling is a snap now with a C++ IDE.

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