Ergonomics
tech guide & how tos..
In order to further strengthen our knowledge of file handling, in this article I am providing you with a couple of sample C programs. Go through each of these programs in detail, write your own version of these programs and run them to develop a deeper understanding of C file handling functions.
This program demonstrates the use of fseek() and ftell() functions to find the size of the file.
Give this source file a name such as findSize.c and then compile it to create the executable file as findSize.exe. You can then run the program by passing it the concerned file name as a command line argument, as -
C:\>findSize myfile.pdf
/*
* Program to find the size of a file
* Demonstrating use of functions - fseek, ftell
* --------------------------------------------------------
*/
#include <stdio.h>
main(int argc,char *argv[])
{
FILE *fp;
char ch;
double size = 0;
void printResult(char *, double);
fp = fopen(argv[1], "r");
if(fp == NULL)
{
printf("\nERROR! File %s could not be open. ", argv[1]);
printf("Check that file exists in same directory where this program is run.\n");
}
else
{
//Position the logical pointer in file to the end of file
fseek(fp, 0, 2);
//Now, tell the position of the pointer
size = ftell(fp);
fclose(fp);
printResult(argv[1], size);
}
}
//Function to print a meaningful file size with appropriate unit
void printResult(char *fileName, double size)
{
if(size<1024)
{
printf("\nThe size of file %s is %d bytes\n", fileName, size);
}
else if(size<1000*1024)
{
size = size*1.0/1024;
printf("\nThe size of file %s is %.2f Kb\n", fileName, size);
}
else
{
size = size*1.0/(1024*1024);
printf("\nThe size of file %s is %.2f MB\n", fileName, size);
}
}Here is another program to demonstrate the use of fseek and ftell and other file handling functions. Note that this program will operate on text files only - it does not make sense to reverse the characters of a binary file.
/*
* Program to Reverse the Contents of a File
* -----------------------------------------
*/
#include<stdio.h>
#include<errno.h>
long getCharCount(FILE *);
void fileCopy(char *, char *);
main(int argc, char *argv[])
{
long nchars;
char ch;
FILE *fp1, *fp2;
fp1 = fopen(argv[1], "r");
if(fp1 == NULL)
{
printf("\nERROR! File %s could not be open. ", argv[1]);
printf("Check that file exists in same directory where this program is run.\n");
return;
}
fp2 = fopen("tempfile", "w");
if(fp2 == NULL)
{
printf("\nERROR! Unable to create temporary file.\n");
return;
}
nchars = getCharCount(fp1);
//Position the logical pointer in file to the last character
fseek(fp1, -1L, 2);
while(nchars)
{
ch = fgetc(fp1); //this moves the logical pointer ahead be 1 char
fputc(ch, fp2);
//Shift logical back by 2 characters
fseek(fp1, -2L, 1);
nchars--;
}
fclose(fp1);
fclose(fp2);
//At this point we have the reversed content in tempfile
//We copy this back to the original file
fileCopy("tempfile", argv[1]);
//Now, we must delete the tempfile
//We use the standard C library function remove()
remove("tempfile");
printf("\nDONE! File %s successfully reversed.\n", argv[1]);
}
//Function to count total number of characters in the given file
long getCharCount(FILE *fp)
{
long count;
fseek(fp, 0, 2); //position logical pointer to end of file
count = ftell(fp);
return count;
}
void fileCopy(char *src, char *destn)
{
FILE *fp1, *fp2;
char ch;
fp1 = fopen(src, "r");
fp2 = fopen(destn, "w");
while((ch = fgetc(fp1)) != EOF) fputc(ch, fp2);
fclose(fp1);
fclose(fp2);
}File Handling in C - Part 1 of 7
File Handling in C - Part 2 of 7
File Handling in C - Part 3 of 7
File Handling in C - Part 4 of 7
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Rajeev Kumar is the primary author of How2Lab. He is a B.Tech. from IIT Kanpur with several years of experience in IT education and Software development. He has taught a wide spectrum of people including fresh young talents, students of premier engineering colleges & management institutes, and IT professionals.
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