Changing writing code to reading code

[binks]

Hi, I have a program that writes out a list of files to a single or multi volume archive. It works very well. I need to write code that can extract the files though. Can most of the work be done by changing the fwrite's to fread's and vice versa?

I know that it won't work 100% just by changing function calls, but I need to first understand the difficulty of this before I can tackle it.

I can post my source code for archiving if needed.

Thanks

[itCbitC]

Hi, I have a program that writes out a list of files to a single or multi volume archive. It works very well. I need to write code that can extract the files though. Can most of the work be done by changing the fwrite's to fread's and vice versa?

Yep! by changing fwrite() to fread() you can read all the data that's been written to the output file.

I know that it won't work 100% just by changing function calls, but I need to first understand the difficulty of this before I can tackle it.

I can post my source code for archiving if needed.

Thanks

It'd be good to post the code, but in a nutshell it is doable by simply changing fwrite() to fread().

[stahta01]

Yep! by changing fwrite() to fread() you can read all the data that's been written to the output file.

It'd be good to post the code, but in a nutshell it is doable by simply changing fwrite() to fread().

And, Changing the fopen command.

Tim S.

[iMalc]

It may be that simple, or there may be much more to it.

[itsme86]

Be aware that if the data file is moved to a different platform, you might run into endianness issues unless you're writing/reading 1 byte at a time.

[binks]

Ok, here is the code archive the files. This code works great.

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define BUFFER_SIZE 4096

// Error function for outputting error
void Error(char *output)
{
    MessageBox(NULL, output, "Error", MB_OK);
    //PostQuitMessage(1);
    exit(1);
}

// Functions to obtain file information
long int GetFileSize(char *fileName)
{
    long int fileSize;

    FILE *fp = fopen(fileName, "rb");

    fseek(fp, 0, SEEK_END);
    fileSize = ftell(fp);
    fclose(fp);
    return fileSize;
}

int min3(size_t a, size_t b, size_t c)
{
      if (a < b)
         return a < c ? a : c;
      else
         return b < c ? b : c;
}

FILE *OpenVolumeFile(char *archiveName, int volume)
{
      char volumeName[256];

      FILE *fArchive;

      if (volume > 0)
          sprintf(volumeName, "%s-%d", archiveName, volume);

      else
         sprintf(volumeName, "%s", archiveName);

      if (!(fArchive = fopen(volumeName, "wb"))) Error("No file handle\n");

      printf("Volume = %d, creating archive file %s\n", volume, volumeName);

      return fArchive;

}

size_t ReadBuffer(FILE *fin, char *buffer, size_t bytesToRead)
{
      size_t bytesRead;

      bytesRead = fread(buffer, 1, bytesToRead, fin);
      if(bytesRead < bytesToRead) Error("fread failure");

      return bytesRead;

}

// Write file header
void WriteArchiveHeaderRecord(FILE* out, char fileName[][256], int fileNameLen, int fileSize)
{
     // write filesize to bin
     if( fwrite(&fileSize, sizeof(fileSize), 1, out) != 1) Error("Could not write filesize header\n");

     // write filename length to bin
     if( fwrite(&fileNameLen, sizeof(fileNameLen), 1, out) != 1) Error("Could not write filename length to header\n");

     // write filename to header
     if( fwrite(fileName, 1, fileNameLen, out) != fileNameLen) Error("Could not write filename to header\n");

}

size_t WriteArchiveHeader(FILE *fArchive, size_t volSize, int numFiles,
                          char fileNames[][256], size_t *fileSizes)
{
      size_t headerSize = sizeof numFiles + sizeof volSize +
                          numFiles * (sizeof *fileSizes + sizeof (size_t));
      int i;

      if( fwrite(&numFiles, sizeof(numFiles), 1, fArchive) != 1) Error("Error writing number of files to bin\n");

      if( fwrite(&volSize, sizeof(volSize), 1, fArchive) != 1) Error("Error writing volume size to bin\n");

      for(i = 0; i < numFiles; i++)
      {
                size_t fileNameLen = strlen(fileNames[i]);

                WriteArchiveHeaderRecord(fArchive, &fileNames[i], fileNameLen, fileSizes[i]);

                printf("Filename: %s\tSize: %i\tFilename Length: %i\n", fileNames[i], fileSizes[i], fileNameLen);

                headerSize += fileNameLen;

      }

      printf("Wrote file header -> Size: %d\n\n", headerSize);

      return headerSize;
}

// Write file to bin
void WriteBuffer(FILE* out, char *buffer, size_t size)
{
    // write data to outfile
    if( fwrite(buffer, 1, size, out) != size)  Error("Error writing file to bin\n");

}

void CreateArchive(char *archiveName, size_t  volSize, int numFiles, char fileNames[][256])
{
      FILE   *fArchive;

      size_t  volBytesLeft;
      size_t  headerSize;
      size_t  fileSizes[numFiles]; // I got rid of the "file" struct

      int     i;
      int     volume = 0;

      for(i = 0; i < numFiles; i++)
            fileSizes[i] = GetFileSize(fileNames[i]);

      fArchive = OpenVolumeFile(archiveName, volSize>0 ? ++volume : 0);

      headerSize = WriteArchiveHeader(fArchive, volSize, numFiles, fileNames, fileSizes);

      if (volSize > 0)
         volBytesLeft = volSize - headerSize;

      else
         volBytesLeft = BUFFER_SIZE + 1; // ensure that it's greater than buffer size

      //volume = 0;

      for(i = 0; i < numFiles; i++)
      {
                size_t fileBytesLeft = fileSizes[i];

                FILE *fData = fopen(fileNames[i], "rb");
                if(fData == NULL)  Error("Error opening file\n");

                printf("File %i: %.2f MB\n", i + 1, (double)fileSizes[i] / 1024 / 1024);

                do
                {
                              char buffer[BUFFER_SIZE];
                              size_t bytesToRead, bytesRead;

                              if(volBytesLeft == 0)
                              {
                                                fclose(fArchive);

                                                volume++;

                                                fArchive = OpenVolumeFile(archiveName, volume);

                                                volBytesLeft = volSize;
                              }

                              bytesToRead = min3(sizeof buffer, fileBytesLeft, volBytesLeft);

                              bytesRead = ReadBuffer(fData, buffer, bytesToRead);

                              WriteBuffer(fArchive, buffer, bytesRead);

                              fileBytesLeft -= bytesRead;

                              volBytesLeft -= bytesRead;

                }
                while(fileBytesLeft > 0);

                fclose(fData);

                printf("Wrote file %i: %s\n\n", i + 1, &fileNames[i]);

      }

      fclose(fArchive);
      printf("Success!");
}


int main()
{
    char fileNames[][256] = {"Test1.zip", "Test2.rar"};
    int volSize = 5;
    int numFiles = 2;

    //CreateArchive(char *archiveName, size_t  volSize, int numFiles, char *fileNames);
    CreateArchive("ArchiveName.bin", (size_t)volSize*1024*1024, numFiles, fileNames);

    return 0;
}

Here is what I have done so far to change it for extracting the files. Help is appreciated!

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define BUFFER_SIZE 4096

// Error function for outputting error
void Error(char *output)
{
    MessageBox(NULL, output, "Error", MB_OK);
    //PostQuitMessage(1);
    exit(1);
}

int min3(size_t a, size_t b, size_t c)
{
      if (a < b)
         return a < c ? a : c;
      else
         return b < c ? b : c;
}

FILE *OpenVolumeToExtract(char *archiveName)
{
      char volumeName[256];

      FILE *fArchive;

      if (!(fArchive = fopen(archiveName, "wb"))) Error("No file handle\n");

      printf("Volume = %d, creating archive file %s\n", volume, volumeName);

      return fArchive;

}

size_t ReadBuffer(FILE *fin, char *buffer, size_t bytesToRead)
{
      size_t bytesRead;

      bytesRead = fread(buffer, 1, bytesToRead, fin);
      if(bytesRead < bytesToRead) Error("fread failure");

      return bytesRead;

}

// Write file header
void ReadArchiveHeaderRecord(FILE* out, char fileName[][256], int fileNameLen, int fileSize)
{
     // write filesize to bin
     if( fread(&fileSize, sizeof(fileSize), 1, out) != 1) Error("Could not read filesize header\n");

     // write filename length to bin
     if( fread(&fileNameLen, sizeof(fileNameLen), 1, out) != 1) Error("Could not read filename length from header\n");

     // write filename to header
     if( fread(fileName, 1, fileNameLen, out) != fileNameLen) Error("Could not read filename from header\n");

}

size_t ReadArchiveHeader(FILE *fArchive, size_t volSize, int numFiles,
                          char fileNames[][256], size_t *fileSizes)
{
      size_t headerSize = sizeof numFiles + sizeof volSize + numFiles * (sizeof *fileSizes + sizeof (size_t));
      int i;

      if( fread(&numFiles, sizeof(numFiles), 1, fArchive) != 1) Error("Error reading number of files from bin\n");

      if( fread(&volSize, sizeof(volSize), 1, fArchive) != 1) Error("Error reading volume size from bin\n");

      for(i = 0; i < numFiles; i++)
      {
                size_t fileNameLen = strlen(fileNames[i]);

                ReadArchiveHeaderRecord(fArchive, &fileNames[i], fileNameLen, fileSizes[i]);

                printf("Filename: %s\tSize: %i\tFilename Length: %i\n", fileNames[i], fileSizes[i], fileNameLen);

                headerSize += fileNameLen;

      }

      printf("Read file header -> Size: %d\n\n", headerSize);

      return headerSize;
}

// Write file to bin
void WriteBuffer(FILE* out, char *buffer, size_t size)
{
    // write data to outfile
    if( fwrite(buffer, 1, size, out) != size)  Error("Error writing file to bin\n");

}

void ExtractArchive(char *archiveName)
{
      FILE   *fArchive;

      size_t  volBytesLeft;
      size_t  headerSize;
      size_t  fileSizes[numFiles]; // I got rid of the "file" struct

      int     i;
      int     volume = 0;

      fArchive = OpenVolumeFile(archiveName, volSize>0 ? ++volume : 0);

      headerSize = WriteArchiveHeader(fArchive, volSize, numFiles, fileNames, fileSizes);

      if (volSize > 0)
         volBytesLeft = volSize - headerSize;

      else
         volBytesLeft = BUFFER_SIZE + 1; // ensure that it's greater than buffer size

      //volume = 0;

      for(i = 0; i < numFiles; i++)
      {
                size_t fileBytesLeft = fileSizes[i];

                FILE *fData = fopen(fileNames[i], "rb");
                if(fData == NULL)  Error("Error opening file\n");

                printf("File %i: %.2f MB\n", i + 1, (double)fileSizes[i] / 1024 / 1024);

                do
                {
                              char buffer[BUFFER_SIZE];
                              size_t bytesToRead, bytesRead;

                              if(volBytesLeft == 0)
                              {
                                                fclose(fArchive);

                                                volume++;

                                                fArchive = OpenVolumeFile(archiveName, volume);

                                                volBytesLeft = volSize;
                              }

                              bytesToRead = min3(sizeof buffer, fileBytesLeft, volBytesLeft);

                              bytesRead = ReadBuffer(fData, buffer, bytesToRead);

                              WriteBuffer(fArchive, buffer, bytesRead);

                              fileBytesLeft -= bytesRead;

                              volBytesLeft -= bytesRead;

                }
                while(fileBytesLeft > 0);

                fclose(fData);

                printf("Wrote file %i: %s\n\n", i + 1, &fileNames[i]);

      }

      fclose(fArchive);
      printf("Success!");
}


int main()
{
    char fileNames[][256] = {"Test1.zip", "Test2.rar"};
    int volSize = 5;
    int numFiles = 2;

    //CreateArchive(char *archiveName, size_t  volSize, int numFiles, char *fileNames);
    CreateArchive("ArchiveName.bin", (size_t)volSize*1024*1024, numFiles, fileNames);

    return 0;
}

[rags_to_riches]

And, Changing the fopen command.

Quoted for truth.

[binks]

Ok, so I have a problem. For the archiver, when I write the filenames, I write the full path. But if your extracting the files, the full path might not exist so it will fail. How can I remove the path upto the filename? Can I use strrchr to find the last '\' and only copy the letters after that? How?

[binks]

Oh, and I have changed some of the function parameters because they weren't necessary for the way of extraction.