trouble writing file

no-reply@allegro.cc (William Labbett) — Wed, 13 Apr 2011 22:25:25 +0000

al_fseek( file, 4, ALLEGRO_SEEK_SET );
   
   pf(" writing version as 2.\n");
   
   al_fwrite32le( file, (int32_t) 2);
   
   al_fseek( file, 4, ALLEGRO_SEEK_SET );
   
   v = al_fread32le( file );
   
   pf(" version is after write is %d.\n",v);

Hi,

in this code, I'm trying to change a number from 1 to 2 in the file.

Since it's an int32_t and the version number is the second number in the file, I call al_fseek(file, 4, ALLEGRO_SEEK_SET) to get to the second int32_t.

After the write, I seek back to the position of the number and read it to v and print it out but it remains 1, not 2 like I'm trying to achieve.

Any ideas why it isn't working ?

no-reply@allegro.cc (Arthur Kalliokoski) — Wed, 13 Apr 2011 22:28:59 +0000

Try an al_fflush() after the write?

no-reply@allegro.cc (William Labbett) — Wed, 13 Apr 2011 22:32:06 +0000

Cheers Arthur. I put one in but it hasn't changed anything.

#SelectExpand
  1void convert_file_from_v1_to_v2( ALLEGRO_FILE *file )
  2{
 
 int num_reps;

 int rep_num;   
 
 int v;
 
 F_REP frep;
 
 if(file == NULL)
 {
    pf(" convert_file_from_v1_to_v2 : file is NULL.\n");
  system("PAUSE");
  exit(1);
 }
 
 al_fseek( file, 0, ALLEGRO_SEEK_SET );
 20
 num_reps = al_fread32le( file);
 
 /* Write 2 as the version number. */
 
 al_fseek( file, 4, ALLEGRO_SEEK_SET );
 
 pf(" writing version as 2.\n");
 
 al_fwrite32le( file, (int32_t) 2);
 
 al_fseek( file, 4, ALLEGRO_SEEK_SET );
 
 v = al_fread32le( file );
 
 pf(" version is after write is %d.\n",v);
 
 pf(" converting file from version 1 to version 2....\n");
 pf(" num_reps = %d.\n", num_reps);
 
 
 al_fseek( file, 8, ALLEGRO_SEEK_SET);
 
 
 for( rep_num = 0; rep_num < num_reps; ++rep_num )
 {
    al_fread( file, &frep, sizeof(F_REP));
 47
    if( frep.type > 1 )
  {
     frep.type += 1;
   
   write_f_rep_( file, rep_num, frep); 
  }
 }
 
 pf("converted file.\n\n");
 
 al_fflush(file);
 
 60}

no-reply@allegro.cc (Matthew Leverton) — Wed, 13 Apr 2011 22:32:54 +0000

What mode are you opening the file as?

no-reply@allegro.cc (William Labbett) — Wed, 13 Apr 2011 22:35:06 +0000

#SelectExpand
  1if(type == LOADED_FILE)
 {
      load :
      
  a_file = al_fopen( fn, "a + b");
  if( a_file == NULL )
  {
    printf(" edit_feature_data() : couldn't load file %s\n", fn);
    return QUIT_DUE_TO_PROBLEM;
  }
    else
  { 
    pf("loaded %s.\n", fn);
  }
  
  al_fseek( a_file, 0, ALLEGRO_SEEK_SET);
  
  num_reps = al_fread32le(a_file);
  
  eof_check_1
  
  frd_file_version = al_fread32le(a_file);
  
  eof_check_1
  
  feature_selected = num_reps - 1;
  
  load_fr = 1;
  
    pf(" num_reps is %d.\n", num_reps);
      pf("loaded frd file. Version is %d.\n", frd_file_version);
 
  if( frd_file_version == 1 && CURRENT_VERSION == 2)
  {
     convert_file_from_v1_to_v2( a_file );
     
     
     al_fclose( a_file );
     
     goto load;
  }

  
  
 }

no-reply@allegro.cc (Matthew Leverton) — Wed, 13 Apr 2011 22:37:30 +0000

I think you want "r+b". Did you check to see if all of your new integers are being appended at the end of the file?

no-reply@allegro.cc (William Labbett) — Wed, 13 Apr 2011 22:47:28 +0000

Thanks. It was "r + b" but I thought I needed to change it to "a + b" as I was trying to write to the file, not just to read from it.

I've changed it back and it's working now .

On to the next problem

/** EDIT : solved */

no-reply@allegro.cc (Thomas Fjellstrom) — Thu, 14 Apr 2011 12:57:51 +0000

yeah, when you add a + to the mode, it means to open in read/write mode. r+ means to open rw, with the file pos at the start of the file, and a+ means to open with the file pos at the end. w+ is a bit different, it'll open the file for reading and writing, but it'll truncate the file first.