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 append mode of opening a file, use the syntax given below −
FILE *fp;
fp =fopen ("sample.txt", "a");If the file doesn’t exist, then, a new file will be created.
If the file exists, the current content will be added to the old content.
Program
Following is the C program for opening a file in append 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");
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 before adding lines are: %d\n",linesCount);
fp=fopen(FILENAME,"a"); //open fine in append mode
while((ch = getchar())!=EOF){
putc(ch,fp);
}
fclose(fp);
fp=fopen(FILENAME,"r");
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 after adding lines are: %d\n",linesCount);
return 0;
}Output
When the above program is executed, it produces the following result −
Total number of lines before adding lines are: 3 WELCOME to Tutorials Its C Programming Language ^Z Total number of after adding lines are: 8