C中的fgets不返回字符串的一部分

Question

I'm totally new in C, and I'm trying to do a little application that searches for a string in a file. My problem is that I need to open a big file (more than 1GB) with just one line inside and fgets return me the entire file (I'm doing test with a 10KB file).

Actually this is my code:

#include <stdio.h>
#include <string.h>


int main(int argc, char *argv[]) {
 char *search = argv[argc-1];

 int retro = strlen(search);
 int pun  = 0;
 int sortida;
 int limit = 10;

 char ara[20];

 FILE *fp; 
 if ((fp = fopen ("SEARCHFILE", "r")) == NULL){
  sortida = -1;
  exit (1);
 }

 while(!feof(fp)){
  if (fgets(ara, 20, fp) == NULL){
   break;
  }
  //this must be a 20 bytes line, but it gets the entyre 10Kb file
  printf("%s",ara);
 }

    sortida = 1;

 if(fclose(fp) != 0){
  sortida = -2;
  exit (1);
 }

 return 0;
}

What can I do to find an string into a file?

I've tried with GREP but it don't helps, because it returns the position:ENTIRE_STRING.

I'm open to ideas.

Answer 1

Try

printf("%s\n",ara);     

Also consider initializing variables before you use them:

char ara[20]={0x0};

Answer 2

You only allocated 20 bytes for the input buffer, but told the fgets to read 20 bytes.

Make this change:

  if (fgets(ara, sizeof(ara)-1, fp) == NULL){ 

remember, if you want 20 characters PLUS the trailing '\\0' that marks the end of the string you have to allocate 21 bytes.