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fseek(file, -1, SEEK_CUR);

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//Open appending to continue expanding file:
///
 fHandle=fopen(creatFileName, "ab+");


//We opened the file for appending, so try to move
//1 byte right before EOF:
///
 fseek(file, -1, SEEK_CUR);   //Move before EOF...

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#include <stdio.h>

//NOTE: These two libraries seem to need to be together
//      to avoid an error message that says:
//
//      "warning: incompatible implicit declaration of built-in
//                function 'memset'":
///
 #include <stdlib.h>
 #include <string.h>


//This is a macro to easily access the first command line
//as the file name the program should use as a big file
//to create:
///
 #define creatFileName   argv[1]
 #define sectors512Count argv[2]


//(bytes_per_sect*sects)-zero_addressing
//
//for completing aligned/full file bytes
///
 #define creatFileSize____512MB          (512*1048576)-1
 #define creatFileSize____20GB0          39070080
 #define creatFileSize____875GBytes      939524096000
 #define creatFileSize____8754ksects     229376000
 #define creatFileSize____875GB512sects  1835008000



int main(int argc, char *argv[])
{
 //Here we just declare the variables
 //to handle the simple big file to create:
 ///
  void *buff;
  FILE *fHandle;
  const char *fName = "hard_disk.img";
  long int numsects = creatFileSize____512MB;


 if(argc<3)
 {
  printf("ERROR: Please specify a file name and a number of 512-byte sectors");
  printf("\r\n");
  return;
 }


 //Let's open (and create or overwrite)
 //the specified file name:
 ///
//if(!fHandle=fopen(creatFileName, "wb+"))  //Create new file...
  if(!fHandle=fopen(creatFileName, "ab+"))  //Append, continue expanding file...
  {
   printf("ERROR: Couldn't open %s\r\n", creatFileName);
   return -1;
  }


  if(!(abs(numsects=atol(sectors512Count))))
  {
   printf("ERROR: Sector count (%ld) must be greater than 0\r\n", numsects);
   return -2;
  }


 //We opened the file for appending, so try to move
 //1 byte right before EOF.
 //
 //These lines are unnecessary since the pointer
 //will be set at the end of file on the first
 //fwrite (in this case) or fread
 //(see http://f.osdev.org/viewtopic.php?f=13&p=258018#p258018)
 ///
//fseek(file, -1, SEEK_CUR);   //Move before EOF...
//fseek(file, 0,  SEEK_SET);   //Move to start... optional...


 //Reserve and clear a 512-byte buffer:
 ///
  buff=malloc(512);
  memset(
         buff,   //Buffer to zero out
         0,      //(int)(unsigned char) value to write (0 in this case)
         512     //Number of bytes to write
        );


 //Write as many 512-byte buffers as the requested
 //size in 512-byte sectors:
 ///
  do
  {
   fwrite(buff, 1, 512, fHandle);
  }
  while(--numsects);


 free(buff);
 fclose(fHandle);

 return 0;
}