Thread: Reverse the Order of Lines

Here's a loose example reversing then replacing original file, you'll have to adapt to suit your needs

Code:

#include <stdio.h>
#define TXT_MAX_LINE_LEN 0xFFFF
typedef long int li;
int main(void)
{
  int _count = 100, count = 0;
  size_t size = (sizeof(li) * _count), clearSize = size;
  li *lines = (li*)memset( malloc( size ), 0, size );
  FILE *oldFile = fopen( ".\example.txt", "r" );
  FILE *curFile = fopen( ".\example_to_be_renamed.txt", "w" );
  char buff[TXT_MAX_LINE_LEN] = {0};
  while ( !feof( oldFile ) )
  {
    lines[count] = ftell( oldFile );
    fgets( buff, TXT_MAX_LIN_LEN, oldFile );
    if ( (++count) == _count )
    {
      lines = (int*)realloc( lines, (size += clearSize) );
      memset( &lines[count], 0, clearSize );
      _count += 100;
    }
  }
  while ( count > 0 )
  {
    fseek( oldFile, lines[--count], SEEK_SET );
    fgets( buff, TXT_MAX_LINE_LEN, oldFile );
    fputs( buff, TXT_MAX_LINE_LEN, curFile );
  }
  free( lines);
  fclose( oldFile );
  fflush( curFile );
  fclose( curFile );
  remove( ".\example.txt" );
  rename( ".\example_to_be_renamed.txt", ".\example.txt" );
  return 0;
}

Edit:Made slight mistake with fgets usage at the start, corrected
Edit:Forgot to add the file flush, corrected

Originally Posted by awsdert

Here's a loose example reversing then replacing original file, you'll have to adapt to suit your needs

Code:

#include <stdio.h>
#define TXT_MAX_LINE_LEN 0xFFFF
typedef long int li;
int main(void)
{
  int _count = 100, count = 0;
  size_t size = (sizeof(li) * _count), clearSize = size;
  li *lines = (li*)memset( malloc( size ), 0, size );
  FILE *oldFile = fopen( ".\example.txt", "r" );
  FILE *curFile = fopen( ".\example_to_be_renamed.txt", "w" );
  char buff[TXT_MAX_LINE_LEN] = {0};
  while ( !feof( oldFile ) )
  {
    lines[count] = ftell( oldFile );
    fgets( buff, TXT_MAX_LIN_LEN, oldFile );
    if ( (++count) == _count )
    {
      lines = (int*)realloc( lines, (size += clearSize) );
      memset( &lines[count], 0, clearSize );
      _count += 100;
    }
  }
  while ( count > 0 )
  {
    fseek( oldFile, lines[--count], SEEK_SET );
    fgets( buff, TXT_MAX_LINE_LEN, oldFile );
    fputs( buff, TXT_MAX_LINE_LEN, curFile );
  }
  free( lines);
  fclose( oldFile );
  fflush( curFile );
  fclose( curFile );
  remove( ".\example.txt" );
  rename( ".\example_to_be_renamed.txt", ".\example.txt" );
  return 0;
}

Edit:Made slight mistake with fgets usage at the start, corrected
Edit:Forgot to add the file flush, corrected

That code is a complete mess though.

For starters: You don't check the return value from malloc(3). You don't check the return value of fopen. You shouldn't control a while loop with feof(3). The way you use fgets(3) is broken. The way you use realloc(3) is broken.

Those are the problems I spotted in 30 s.

If you are going to post a "complete" solution and disregard the homework rules, at least post one that is correct.

A linked list can make it easy too.

Code:

while (fgets(buffer, sizeof buffer, read_me) != NULL) {
   elem = make_node(buffer);
   list_push(&head, elem);
}

/* later */

while ((cur = list_pop(&head)) != NULL) {
   fputs(cur->line, write_me);
   delete_node(cur);
}

Requisite parts being available of course