Reading a File Line By Line

by Dave Sinkula on Jan 12th, 2005

While not terribly difficult, first timers may not know the functions to look up and use. Here is some basic code for reading a file one line at a time. The contents of the file are printed to the stdout.

C Code Snippet (Toggle Plain Text)

#include <stdio.h>
 
int main ( void )
{
   static const char filename[] = "file.txt";
   FILE *file = fopen ( filename, "r" );
   if ( file != NULL )
   {
      char line [ 128 ]; /* or other suitable maximum line size */
 
      while ( fgets ( line, sizeof line, file ) != NULL ) /* read a line */
      {
         fputs ( line, stdout ); /* write the line */
      }
      fclose ( file );
   }
   else
   {
      perror ( filename ); /* why didn't the file open? */
   }
   return 0;
}
 
/* file.txt
This text is the contents of the file named, "file.txt".
 
It is being used with some example code to demonstrate reading a file line by
line. More interesting things could be done with the output, but I'm trying to
keep this example very simple.
*/
 
/* my output
This text is the contents of the file named, "file.txt".
 
It is being used with some example code to demonstrate reading a file line by
line. More interesting things could be done with the output, but I'm trying to
keep this example very simple.
*/

Comments on this Code Snippet

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Feb 9th, 2006

Re: Reading a File Line By Line

I thinks instead of depending on the length of the line (which can be variable depeding on the type of editor and its settings).I think it'll be better to look for '\n' which is line separator.

khuman_nb

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Mar 19th, 2006

Re: Reading a File Line By Line

Quote ...

I thinks instead of depending on the length of the line (which can be variable depeding on the type of editor and its settings).I think it'll be better to look for '\n' which is line separator.

Then you would be describing doing this "by character" rather than by line. Otherwise you are wonderfully overcomplicating this with dynamic memory allocation a la C++'s std::string.

Dave Sinkula

long time no c

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Aug 24th, 2006

Re: Reading a File Line By Line

hi this is great!

can you tell me how do i put each line to an array?

darylcharm

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since Aug 2006

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Jan 8th, 2007

Re: Reading a File Line By Line

hi guys
i just modified the one i got here: this will read line by line from a text file then stored every line to an array;

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <conio.h>
#include <ctype.h>
#include <ctype.h>
#include <time.h>
#include <sys/types.h>

int main ( void )
{
static const char filename[] = "data.txt";
FILE *file = fopen ( filename, "r" );
int i, j;
char arra[128][128];
char line[128]; /* or other suitable maximum line size */

for(i=0; i<128; i++)
for(j=0; j<128; j++)
arra[i][j] = '\0';

for(i=0; i<128; i++)
line[i] = '\0';

if ( file != NULL )
{

i=0;

while ( fgets ( line, sizeof line, file ) != NULL ) /* read a line */
{

strcpy(arra[i], line);
printf("array ----> %s ", &arra[i]);
i++;

}
fclose ( file );
}
else
{
perror ( filename ); /* why didn't the file open? */
}

return 0;
}

Tmo

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since Jan 2007

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Nov 12th, 2008

Re: Reading a File Line By Line

i want to Read a line from file then compare it to a sentense(GPS Sentence) and if its match(valid) then display this line else display Error

plz advice
Regards

tirmizi

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since Nov 2008

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Feb 13th, 2009