Displaying portion of text from text file in C - c

Question

I have a text file and I wanted to extract only a specific part of it at a particular time.For that ,I used ftell() while writing to note the start and end positions and then use fseek() to jump to that particular location.
int main()
{
FILE *fp=fopen("myt","w+");
char s[80];
printf ( "\nEnter a few lines of text:\n" ) ;
while ( strlen ( gets ( s ) ) > 0 ) //user inputs random data
{ //till enter is pressed
fputs ( s, fp ) ;
fputs ( "\n", fp ) ;
}
long int a=ftell(fp);
fputs("this line is supposed to be printed only ",fp);//line to be
// displayed
fputs("\n",fp);
long int b=ftell(fp);
printf("start is %ld",a);
printf("\nend is %ld",b);
printf("here is the data...\n");
rewind(fp);
fseek(fp,a,SEEK_CUR); //move to the starting position of text to be
//displayed
char x[1000];
fgets(x,b-a,SEEK_CUR);
printf("%s",x);
return 1;
}
I tried this but face a unexpected abnormal termination of program.Please guide me as to how correctly implement my task.

Answer 1

You want this:
Comments starting with //// are mine
#include <stdio.h> //// include required header files
#include <string.h>
int main()
{
FILE *fp = fopen("myt", "w+");
if (fp == NULL) //// test if file has been opened sucessfully
{
printf("Can't open file\n");
return 1; //// return 1 in case of failure
}
char s[80];
printf("\nEnter a few lines of text:\n");
while (strlen(gets(s)) > 0) //user inputs random data
{ //till enter is pressed
fputs(s, fp);
fputs("\n", fp);
}
long int a = ftell(fp);
fputs("this line is supposed to be printed only ", fp);//line to be
// displayed
fputs("\n", fp);
long int b = ftell(fp);
printf("start is %ld", a);
printf("\nend is %ld", b);
printf("here is the data...\n");
rewind(fp);
fseek(fp, a, SEEK_CUR); //move to the starting position of text to be
//displayed
char x[1000];
fgets(x, sizeof(x), fp); //// the usage of fgets was totally wrong
printf("%s", x);
return 0; //// return 0 in case of success, no one
}
Disclaimer: The first part reading the strings using gets is still sloppy, you should never use gets, it's an old deprecated function. Use fgets instead.