File is collection of records or is a place on hard disk, where data is stored permanently.
Need of files
Entire data is lost when a program terminates.
Storing in a file preserves the data even if, the program terminates.
If you want to enter a large amount of data, normally it takes a lot of time to enter them all.
We can easily access the content of files by using few commands.
You can easily move your data from one computer to another without changes.
By using C commands, we can access the files in different ways.
Operations on files
The operations on files in C programming language are as follows −
- Naming the file
- Opening the file
- Reading from the file
- Writing into the file
- Closing the file
Syntax
The syntax for declaring a file pointer is as follows −
FILE *File pointer;
For example, FILE * fptr;
The syntax for naming and opening a file pointer is as follows −
File pointer = fopen ("File name", "mode");For example, to read mode of opening the file, use the following syntax −
FILE *fp
fp =fopen ("sample.txt", "r");If the file does not exist, then fopen function returns NULL value.
If the file exists, then data is read successfully from file.
Example
Following is the C program for opening a file in read mode and counting number of lines present in a file −
#include<stdio.h>
#define FILENAME "Employee Details.txt"
int main(){
FILE *fp;
char ch;
int linesCount=0;
//open file in read more
fp=fopen(FILENAME,"r"); // already existing need to be open in read mode
if(fp==NULL){
printf("File \"%s\" does not exist!!!\n",FILENAME);
return -1;
}
//read character by character and check for new line
while((ch=getc(fp))!=EOF){
if(ch=='\n')
linesCount++;
}
//close the file
fclose(fp);
//print number of lines
printf("Total number of lines are: %d\n",linesCount);
return 0;
}Output
When the above program is executed, it produces the following result −
Total number of lines are: 3