C - File Handling

Sometime it is necessary to store the output in a file for permanent storage instead of just displaying it. In C Language, this can be done with the help of file handling.

Using file handling we can do the following operations on a file.

Create a new File
Open an existing File
Closing a file
Read from a file
Write in a file
Searching in a file
Updating in a file
Deleting in a file
Rename a file

There are many functions in C library which is use to open, read, write, search and close a file. A list of file functions is given below:

File handling modes tells the compiler what action to be perfom on the file eg read, write, append etc. File handling modes are listed below:

If you are going to handle binary files then you can use below mentioned access modes:

fputc() function: Use to write a single character into a file.

Example 1: WAP to input a character and write in a file.

#include<stdio.h>
#include<conio.h>
void main()
{
    char a;
    FILE *fp;
    clrscr();
    fp = fopen("file.txt","w");
    printf("Enter character: ");
    a = getchar();
    fputc(a,fp);
    fclose(fp);
}

/* Use while loop to write a string in the file. '\r' is use for carriage return.*/
while(a!='\r')
{
    a = getche();
    fputc(a,f);
}

Example 2: WAP to Input a character and append in a file.

#include<stdio.h>
#include<conio.h>
void main()
{
    char a;
    FILE *fp;
    clrscr();
    fp = fopen("file.txt","a");
    printf("Enter character");
    a = getchar();
    fputc(a,fp);
    fclose(fp);
}

#include<stdio.h>
#include<conio.h>
void main()
{ 
    FILE *fp;
    char ch;
    clrscr();
    fp=fopen("file.txt","r");
    ch = fgetc(fp);
    printf("%c",ch);
    close(fp);
    getch();
}

#include<stdio.h>
#include<conio.h>
void main()
{ 
    FILE *fp;
    char ch;
    clrscr();
    fp=fopen("file.txt","r");
    while((ch=fgetc(fp))!=EOF)
    {
       printf("%c",ch);
    } 
    close(fp);
    getch();
}

fputs() function: Write a line of characters into a file.

Example 4.1: WAP to write a string in a file.

#include<stdio.h>
#include<conio.h>
void main()
{
    FILE *fp;
    clrscr();
    fp=fopen("file.txt","w");
    fputs("Hello fgets - fputs example",fp);
    fclose(fp);
}

Example 4.2: WAP to input a string and write in a file.

#include<stdio.h>
#include<conio.h>
void main()
{
    FILE *fp;
    char ch[80];
    clrscr();
    fp=fopen("file.txt","a");
    printf("Enter sentance:");
    gets(ch);
    fputs(ch, fp);
    fclose(fp);
}

fgets() function: Read a line of characters from the file.

Example 5: fgets function

#include<stdio.h>
#include<conio.h>
void main()
{
    FILE *fp;
    char text[80];
    clrscr();
    fp=fopen("file.txt","r");
    printf("%s",fgets(text,80,fp));
    fclose(fp);
    getch();
}

fprintf() function: Use to write set of characters into the file.

Example 6: fprintf() function

#include<stdio.h>
#include<conio.h>
void main()
{
    FILE *fp;
    clrscr();
    fp = fopen("file.txt", "w");
    fprintf(fp, "Hello fprintf example.");
    fclose(fp);
    getch();
}

fscanf() function: Use to read set of characters from the file. It reads a word from file and returns EOF at the end of file.

Example 7: fscanf() function

#include<stdio.h>
#include<conio.h>
void main()
{
    FILE *fp;
    char text[255];
    clrscr();
    fp = fopen("file.txt", "r");
    while(fscanf(fp, "%s", text)!=EOF)
    {
        printf("%s ", text);
    }
    fclose(fp);
    getch();
}

Example 8: Store employee information as entered by user. Store employee id, name, salary and display it.

#include<stdio.h>
#include<conio.h>
void main()  
{  
    FILE *fptr;  
    int id;  
    char name[30];
    float salary;
    clrscr();
    fptr = fopen("emp.txt", "w+");
    if (fptr == NULL)  
    {  
        printf("File does not exists \n");  
        return;  
    }  
    printf("Enter the id: ");  
    scanf("%d", &id);  
    fprintf(fptr, "Id= %d\n", id);  
    printf("Enter the name: ");  
    scanf("%s", name);  
    fprintf(fptr, "Name= %s\n", name);  
    printf("Enter the salary: ");  
    scanf("%f", &salary);  
    fprintf(fptr, "Salary= %.2f\n", salary);  
    fclose(fptr);  
    getch();  
}

fseek() function: Use to set the file pointer to the specified offset. It is used to write data into file at desired location.

There are 3 constants used in the fseek() function: SEEK_SET, SEEK_CUR and SEEK_END.

Example 9: fseek() function

#include<stdio.h>
#include<conio.h>
void main()
{
    FILE *fp;
    clrscr();
    fp = fopen("file.txt","w+");
    fputs("This is fseek function", fp);
    fseek( fp, 7, SEEK_SET);
    fputs("replaced text", fp);
    fclose(fp);
    getch();
}

C rewind() function: Sets the file pointer at the beginning of the stream. It is useful if you have to use stream many times.

Example 10: rewind() function

#include<stdio.h>
#include<conio.h>
void main()
{  
    FILE *fp;  
    char c;  
    clrscr();  
    fp=fopen("file.txt","r");  
    while((c=fgetc(fp))!=EOF)
    {  
        printf("%c",c);  
    }  
    rewind(fp);//moves the file pointer at beginning of the file  
    while((c=fgetc(fp))!=EOF)
    {  
        printf("%c",c);  
    }  
    fclose(fp);    
    getch();    
}

As you can see, rewind() function moves the file pointer at beginning of the file that is why "this is simple text" is printed 2 times. If you don't call rewind() function, "this is simple text" will be printed only once.

ftell() function: returns the current file position of the specified stream. We can use ftell() function to get the total size of a file after moving file pointer at the end of file.

Example 11: ftell() function

#include<stdio.h>
#include<conio.h>
void main()
{
    FILE *fp;  
    int length;
    clrscr();
    fp = fopen("file.txt", "r");
    fseek(fp, 0, SEEK_END);
    length = ftell(fp);  
    fclose(fp);  
    printf("Size of file: %d bytes", length);  
    getch();  
}

fread(), fwrite() function: use to read and write a record in a data file

Example 12: fread(), fwrite() function

#include<stdio.h>
#include<conio.h>
struct student
{
    int rollno;
    char name[20];
};

void main()
{
    struct student st, st2;
    clrscr();
    printf("Enter Rollno and Name:");
    fflush(stdin);
    scanf("%d",&st.rollno);
    fflush(stdin);
    gets(st.name);

    FILE *fp;
    fp=fopen("record.dat", "a");
    fwrite(&st, sizeof(st), 1, fp);
    fclose(fp);

    fp=fopen("record.dat", "r");
    //fread(&st2, sizeof(st2), 1, fp); //read a single record
    while(fread(&st2, sizeof(st2), 1, fp))
    {
        printf("\nRollno = %d", st2.rollno);
        printf("\nName= %s", st2.name);
    }
    fclose(fp);
    getch();
}

rename() function: Use to rename a file. You can use variable or file name inside a rename function

Example 13: Input a filename and rename it with new name.

#include<stdio.h>
#include<conio.h>
void main()
{
    char oldname[50];
    char newname[50];
    clrscr();
    //rename("abc.dat","student.dat"); //using filename
    rename(oldname,newname); //using variable name
    getch();
}

remove() function: Use to remove a file. You can use variable or file name to a rename function

Example 14: Input a filename and remove it.

#include<stdio.h>
#include<conio.h>
void main()
{
    char filename[50];
    clrscr();
    //remove("student.dat"); //using filename
    remove(filename); //using variable name
    getch();
}