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pranavjec 0 Newbie Poster

hi guys,

i have no idea how these lines work the given c program(see attachment).the program is about Read SEG-Y input data from disk file (stream of bytes)
to properly structured SEG-Y with proper IRGs on tape.The program didnt include any path of the file.does theses line works as path (i.e.frm the tape to the disk) as well.
fd_in_segy = open(argv[1],O_RDONLY);
fd_out_segy = open(argv[2],O_WRONLY);
i m bit confussed

bye

#include <stdio.h>
#include <fcntl.h>
#include <string.h>
/*
                       segyread 

   Read SEG-Y input data from disk file (stream of bytes)
   to properly structured SEG-Y with proper IRGs on tape.

  

   At command line supply following items:

   Program   Input Segy file              Tape device           tpf file   

   segyread /net/scdata1/input_segy     /dev/rmt/tps3d1nsv     /net/scdata1/khoraghat.tpf

*/

char tpf_file_name[120]; 

int  fd_in_segy;          /* SEGY          input  file descriptor */
int  fd_out_segy;         /* SEGY          output file descriptor */

FILE *tpf;                /* tpf           input  file pointer    */

main(int argc, char **argv)
{
 unsigned char tphead[3200];
 unsigned char trace[16000];
 short int bhead[200]; 
 int   i, nrec=0, recsize=0;
 int   trace_count=0; 

                                      /* Open SEG-Y disk file for reading  */

   fd_in_segy = open(argv[1],O_RDONLY);

   if ( fd_in_segy == NULL)
      {
         printf("Problem in opening *SEG Y data input file *\n");
         return(1);
      }
                                      /* Open SEG-Y Tape file for output   */

   fd_out_segy = open(argv[2],O_WRONLY);

   if ( fd_out_segy == NULL)
      {
         printf("Problem in opening *SEG Y data output file *\n");
         return(2);
      }

                                      /* Open tpf ASCII file for input  */

    tpf = fopen(argv[3],"r");
    if (tpf == NULL)
       {
             printf("Problem in opening *tpf input file *\n");
             return(4);
       }


 fscanf(tpf, "%d%d",&nrec,&recsize);
 printf("Record no.:%d recsize=%d\n",nrec,recsize);  

 if (nrec == 1 && recsize == 3200 ) 
    {
       if ( recsize != read(fd_in_segy, tphead, recsize))
          { 
            printf("Problem in reading tape header nbread=%d\n",recsize);
            exit(1);
          }
                                       /* Write tape header to output tape */  

          if ( recsize != write(fd_out_segy, tphead, recsize) )
             { 
               printf("Problem in writing tape header nbread=%d\n",recsize);
               exit(1);
             }

                                       /* read next record from tpf file */
       fscanf(tpf, "%d%d",&nrec,&recsize);

       if ( nrec == 1 && recsize == 400 ) 
          {
            if (  recsize != read(fd_in_segy, bhead, recsize) ) 
               { 
                 printf("Problem in reading binary header =%d\n",recsize);
                 exit(1);
                }

             if ( recsize != write(fd_out_segy, bhead, recsize) ) 
               { 
                 printf("Problem in writing binary header =%d\n",recsize);
                 exit(1);
                }
          }
       else
          { 
             printf("Binary header not available, check and retry \n");  
             exit(1);
          }
    }
 else 
    {
      printf("Input data is not SEG-Y check, try with correct data\n");
      exit(1);
    }
        
               /* Read number of traces with their corresponding sizes */  


while (fscanf(tpf, "%d%d",&nrec,&recsize) != EOF)
     {
       for (i=0;i<nrec;i++)
          {
             trace_count++;
             if ( recsize != read(fd_in_segy, trace, recsize) )
                {
                  printf("Problem in reading trace no: %d\n",trace_count);
                  exit(0);
                }

             if ( recsize != write(fd_out_segy, trace, recsize) ) 
                {
                  printf("Problem in writing trace no: %d\n",trace_count);
                  exit(0);
                }
              
          }
     }
     printf("Total no. of traces read and processed =%d\n",trace_count); 
     printf("JOB COMPLETED SUCCEFULLY\n"); 
}
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