File Handling in C

A file is a place on disk where a group of related data is stored. Like most other High Level Languages, C supports a number of functions that have the ability to perform basic file operations which includes:

1. Naming the file

2. Opening a file

3. Closing the file

4. Reading data from a file

5. Writing data to a file

Functions of file handling

Function Name Operation                                                  

fopen() : Create a file for use and/or Open an existing file.

fclose() : Close a file which has been opened.

getc() : Read a character from a file.

putc() : Write a character to a file.

fprintf() : Write a set of data values to a file.

fscanf() : Read a set of data values from a file.

getw() : Read an integer from a file.

putw() : Read an integer into a file.

fseek() : Set the position to the desired point in a file.

ftell() : Give current position in the file.

rewind() : Set the position to the beginning of a file.

Defining and Opening a file

For defining a file we have to include three things

• File name
• Data Structure
• Purpose

File name is a string of characters that make a valid file name for operating system. E.g., ABC.C, XYZ.txt etc.

Data Structure of a file is defined as FILE in the library of Standard Input Output function definition.

Purpose includes that in which mode we are to open a file i.e., read(r), write(r) or append(a) mode.

Syntax for defining a file

FILE *fp;

fp=fopen("File_name","mode");

Here FILE is a data structure and fp is a pointer of type FILE.

Simple Program to Read data from keyboard and write it to a file "File_name" and again read the same data from file the same file and display it on the screen.

#include<conio.h>

#include<stdio.h>

void main()

{

FILE *fp;

char c;

printf("Enter data into file:\n");

fp=fopen("File_name","w");

while((c=getchar())!=EOF)

{

putc(c,fp);

}

fclose(fp);

printf("Data Output:\n");

fp=fopen("File_name","r");

while((c=getc(fp)!=EOF)

{

printf("%c",c);

}

fclose(fp);

getch();

}

Error Handling in C

It is possible that an error may occur during Input/Output operation on a file. Typical error situation include

1. Trying to read beyond the EOF (End Of File).

2. Device Overflow.

3. Trying to use a file that has not been opened.

4. Trying to perform an operation on a file, when the file is opened for another type of operation.

5. Opening an file with an invalid name.

6. Attempting to write to a write protected file.

C language provides some error handling functions to handle these kind of errors

• feof(): This function can be used to test for End of File condition. It takes a file pointer as its argument and returns a non-zero integer value if all the data from the specified file has been read. It returns zero otherwise.
• ferror(): This function reports the status of the indicated. It takes file pointer as its argument and returns a non-zero value if an error has been detected up to that point during the processing. It returns zero otherwise.