Grep a string from pdb file

Hi,
Im new to c programming.
I have one pdb file. i want to extract a string starting with ATOM and store it in a text file.

here is my program,

Code:

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<fcntl.h>
#define size 50
main()
{
char temp[300],*ptr;
char sname[50],ws[50],buf[50],buf1[50],field[32];
FILE *file,*file1;
int n;
printf("Enter the Filename\n");
scanf("%s",sname);
file=fopen(sname,"r");
printf("Enter the Word to Search\n");
scanf("%s",ws);
file1=fopen("grep.txt","w");
while(fgets(temp,200,file)!=NULL)
{
ptr=strstr(temp,ws);
if(ptr!=NULL)
fprintf(file1,"%s",ptr);
}
fclose(file);

strstr function extract the intermediate ATOM and ATOMS too. but i want a string staring with ATOM.

Thanks in advance..

Have you tried strnstr()? Then you can restrict the length.

Originally Posted by Subsonics

Have you tried strnstr()? Then you can restrict the length.

when i use strnstr() it gives the following error
(.text+0xbd): undefined reference to `strnstr'
collect2: ld returned 1 exit status

Hm, yeah it's not a standard C function I noticed your fcntl.h and thought it belonged to POSIX but apparently it's a BSD extension. That leaves you to implement a simple parsing function yourself, either as a second step to what strstr catches or make something from scratch that scans the lines from fgets.

BTW, you should indent the code, that way you might get more responses here.

Originally Posted by Subsonics

Hm, yeah it's not a standard C function I noticed your fcntl.h and thought it belonged to POSIX but apparently it's a BSD extension. That leaves you to implement a simple parsing function yourself, either as a second step to what strstr catches or make something from scratch that scans the lines from fgets.

BTW, you should indent the code, that way you might get more responses here.

sorry I can't understand yours plz explain it in a clear manner.

Code:

#include<stdio.h>
#include<string.h>
int main()
{
  const char filename[] = "3IL8.pdb";
  char temp[300],*ptr;
  FILE *file,*file1;
  file = fopen(filename, "r");
  file1=fopen("grep.txt","w");
  while(fgets(temp,200,file)!=NULL)
  {
    ptr=strstr(temp,"ATOM");
    if(ptr!=NULL)
    fprintf(file1,"%s",ptr);  
  }  
  fclose(file);
}

I want the strings starting with "ATOM". but this program output will contain "ATOMS" and "intermediate ATOM" too.