Thread: Writing to a text file

I've been away from programming for a while, and fear that I may have over-indulged in some form of brain killing activity...If one of you good people would be kind to point out what I'm doing wrong with this (simple) program, I'd be most gratefull...

Code:

#include <stdio.h>


#define STR_SIZE sizeof(struct TEST)
#define C_SCANF while(getchar() != '\n');

struct TEST{
   char msg[100];
   int  number[2];
   }msg[10];


int main(void)
{

int count = 0;

FILE *fp;


if ( (fp=fopen("test.TXT","rt+"))== NULL)
     {
      if ( (fp=fopen("test.TXT","wt"))== NULL)
         {
          printf("\nUnable to create test file");
          return 1;
         } 
      }


while(count < 10)
  {
   printf("\nEnter a message > ");
   fgets(msg[count].msg,800,stdin);

   printf("\nEnter a number (I don't care) > ");
   scanf("%d", msg[count].number);
   C_SCANF;

   fseek (fp,(count)*STR_SIZE, SEEK_SET);
   fwrite(&msg,STR_SIZE,1,fp);

   count++;
   }
}

Thanks for any help..

Well, yes... that helps.... I'm off to cower in a corner, I'm becoming worse at this...

Oooh I have a related question...

Am I correct in assuming that fseek can only be used with binary files?

Originally posted by Inept Pig
Oooh I have a related question...

Am I correct in assuming that fseek can only be used with binary files?

no.

A most insightful answer, Thanks....

> Am I correct in assuming that fseek can only be used with binary files?
Yes and no

You can't use fseek() in the way you have used it - namely calculating the position.

You can however use ftell() to tell you where you are, then use that result in future fseek() calls.

Incomplete example to read a random line from a file.

Code:

unsigned long positions[10];
int i = 0;

// produce an index of the file
positions[i++] = ftell(fp);
while ( fgets( buff, BUFSIZ, fp ) != NULL ) {
    positions[i++] = ftell(fp);
}

// use the index to select a random line in a file
int j = rand() % i;
fseek( fp, positions[j], SEEK_SET );
fgets( buff, BUFSIZ, fp );
printf( "Random line from file %s", buff );

This technique is pretty useful if your text file is very long, and fairly constant (say a dictionary). You can jump to the start of a line without having to read each line in turn from the start of the file.

Splendid!

Thanks for answering in such detail.