Ad:

C Discussion Thread
Unsolved
Views: 12815

Jan 7th, 2007

Read file with unknown buffer length

Expand Post »

I try read a story text file using c. the problem is i want one paragraf in one variabel. i am confuse how much i should alocate the buffer size?

C Syntax (Toggle Plain Text)
#include <stdio.h>  
int main() {    
char buf[255]; <<HOW MUCH SHOULD WE ALOCATE TE BUFFER?
FILE* fp = fopen("somefile.txt","r");    
  if( fp == NULL)    {       
     printf("Can't open the file\n");       
     return 1;    
  }    // read each line of the file    
 
while( fgets(buf,sizeof(buf),1,fp) != NULL)    {       
  // count the lines or do other stuff here    
}    
// close the file    fclose(fp);    return 0; }
#include <stdio.h>  
int main() {    
char buf[255]; <<HOW MUCH SHOULD WE ALOCATE TE BUFFER?
FILE* fp = fopen("somefile.txt","r");    
  if( fp == NULL)    {       
     printf("Can't open the file\n");       
     return 1;    
  }    // read each line of the file    
 
while( fgets(buf,sizeof(buf),1,fp) != NULL)    {       
  // count the lines or do other stuff here    
}    
// close the file    fclose(fp);    return 0; }

:cheesy

sorry for my bad english, i hope u understand)

Similar Threads

xibnoe

Reputation Points: 10

Solved Threads: 0

Newbie Poster

Offline

7 posts
since Jun 2006

Permalink

Jan 7th, 2007

Re: Read file with unknown buffer length

Well, since you're only reading in one line of the file at a time, you should have some idea of how long the lines will be. Choose a buffer size that is large enough to hold these requirements. Since we don't know what files you're planning to read, we can't give a perfect guess.

This question is similar to "how large should I make this field in my database?" Well, the answer is however much you need.

In C++ this problem doesn't exist since you can use strings to dynamically allocate the memory needed to store the data.

John A

Team Colleague

Reputation Points: 2240

Solved Threads: 338

Vampirical Lurker

Offline

5,055 posts
since Apr 2006

Permalink

Jan 7th, 2007

Re: Read file with unknown buffer length

you have a couple options: (1) put each of the strings in an array of strings, or (2) keep a linked list of the lines that are read.

Here is an example of using the array.

C Syntax (Toggle Plain Text)
#include <stdio.h>  
int main() {    
int linecount = 0;
char *array[255] = {0}; // hold 255 lines
 
char buf[255]; <<HOW MUCH SHOULD WE ALOCATE TE BUFFER?
FILE* fp = fopen("somefile.txt","r");    
  if( fp == NULL)    {       
     printf("Can't open the file\n");       
     return 1;    
  }    // read each line of the file    
 
while( fgets(buf,sizeof(buf),1,fp) != NULL)    {       
  // count the lines or do other stuff here    
   array[linecount] = malloc(strlen(buf)+1);
   strcy(array[linecount],buf);
   linecount++;
}    
// close the file
#include <stdio.h>  
int main() {    
int linecount = 0;
char *array[255] = {0}; // hold 255 lines

char buf[255]; <<HOW MUCH SHOULD WE ALOCATE TE BUFFER?
FILE* fp = fopen("somefile.txt","r");    
  if( fp == NULL)    {       
     printf("Can't open the file\n");       
     return 1;    
  }    // read each line of the file    
 
while( fgets(buf,sizeof(buf),1,fp) != NULL)    {       
  // count the lines or do other stuff here    
   array[linecount] = malloc(strlen(buf)+1);
   strcy(array[linecount],buf);
   linecount++;
}    
// close the file

Ancient Dragon

Sponsor

Team Colleague

Featured Poster

Reputation Points: 5608

Solved Threads: 2283

Retired and Enjoying Life

Offline

21,963 posts
since Aug 2005

Permalink

Jan 7th, 2007

Re: Read file with unknown buffer length

Click to Expand / Collapse Quote originally posted by xibnoe ...

I try read a story text file using c. the problem is i want one paragraf in one variabel. i am confuse how much i should alocate the buffer size?

Unless you know how many characters in your paragraph, you can't just allocate a buffer. As AD suggests, you can set up an array of pointers, assuming you know how many paragraphs you need. There's another function you can use named realloc(). You malloc() for the first line you read, then realloc() to add more space for each line additional line you read. When you get to the end of the paragraph, increment the paragraph count (like AD did) and start again with a new malloc().

WaltP

Moderator

Reputation Points: 3281

Solved Threads: 896

Posting Sage

Offline

7,753 posts
since May 2006

This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.

Previous Thread in C Forum Timeline: How to deal with integer overflow

Next Thread in C Forum Timeline: Try This

DaniWeb Message

Cancel Changes

User Name
Password