File Handling in c

C language, allows to work with all file operations, like create, open, read, write, append, seek, delete and closing a file using FILE pointer data type.

Advantages of File handling

1. Stored data in a file does not depends on computer power, It can be stored for long time.
2. A file can hold large amount of data.
3. A file can be transferred easily, from one to another computer or over network.
4. A file data can be used a input.

File Pointer data type in C

C language provide file pointer data type to perform operations with file.

Syntax

FILE *<pointer_variable_name>;

FILE must be in capital letters.

File related operations in c

In C, with files, following operation may perform.

1. Creating a new file
2. Opening a file
3. Reading a file
4. Writing a file
5. Searching a file
6. Append a file
7. Closing a file
8. Deleting a file

In C, For reading or writing a file different file modes are provided they are:

File Access Mode	Description
r	Opens a file in read only mode
w	Opens a file in write only mode
a	Opens a file, If content exists, it does not delete the existing content. It starts writing to the file from the end of existing content.
rb	This mode works with binary file. Opens a binary file in read only mode.
wb	Opens a binary file in write only mode.
ab	Opens a binary file and start writing data from the end of existing content of a file.
r+	Opens a file for both read and write operations.
w+	Opens a file for both read and write operations.
a+	Opens a file for both read and append operations.
rb+	Opens a binary file for both read and write operations.
wb+	Opens a binary file for both read and write operations.
ab+	Opens a binary file for both read and append operations.

Open a File in C

To work with file in c, a file must be open first. To open c, provides fopen() function. fopen() opens and also creates a file, if not exist depends on provided file access mode.

Syntax

FILE* fopen(const char *file_name, const char *access_mode);

fopen() takes two arguments

const char *file_name	File name with extension to work with
const char *access_mode	Mode to perform operation on file, like r,w,a etc.

Fopen return value

fopen() returns a file pointer if file opens successfully and return NULL if file not found.

Example

#include<stdio.h>
#include<stdlib.h>

void main()
{
    // Declaring a file pointer
    FILE* fileptr;
    // Opens a file in read only mode
    fileptr = fopen("myfile.txt", "r");
}

Check file exists or not in c

#include<stdio.h>
#include<stdlib.h>

void main()
{
    // Declaring a file pointer
    FILE* fileptr;
    // Opens a file in read only mode
    fileptr = fopen("myfile.txt", "r");
    // Returns NULL, if file not exists
    if (fileptr == NULL) {
        printf("File does not exist");
    }

}

Create a File in C

In C, fopen() when used with w, w+, wb, wb+, a, a+, ab, and ab+ these file modes, creates a new file with given name, if not found.

Example

#include<stdio.h>
#include<stdlib.h>

void main()
{
    // Declaring a file pointer
    FILE* fileptr;
    // Opens a file in write only mode
    // Creates a file, if not exists
    fileptr = fopen("myfile.txt", "w"); 
}

Reading From a File in c

To read a file, c provides different functions.

fread()	Reads from a binary file
fgetc()	Reads a single character from file
fgets()	Reads a single line from file
fscanf()	Reads from file using formatted string.

File should be opened in r access mode.

Example

#include<stdio.h>
#include<stdlib.h>

void main()
{
    // Declaring a file pointer
    FILE* fileptr;
    char chr;
    // Opens a file in write only mode
    fileptr = fopen("myfile.txt", "r"); 

    while ((chr = fgetc(fileptr)) != EOF) {
        printf("%c", chr);
    }
}

Writing a File in c

To write a file, C provides following function

fprintf()	Write formatted string to a file
fwrite()	Writes given bytes to a binary file
fputc()	Writes a single character to file
fputs()	Writes a single line to file

Example

#include<stdio.h>
#include<stdlib.h>

void main()
{
    // Declaring a file pointer
    FILE* fileptr;
    char chr;
    // Opens a file in write only mode
    fileptr = fopen("myfile.txt", "w"); 

    fputc("z", fileptr);
}

Appending content of File in c

Appending means to write without deleting or removing existing contents of file. New content adds at the end of file previous content.

File must be opened in w access mode.

Example

#include<stdio.h>
#include<stdlib.h>

void main()
{
    // Declaring a file pointer
    FILE* fileptr;
    char chr;
    // Opens a file in append only mode
    fileptr = fopen("myfile.txt", "a"); 

    fputc("y", fileptr);
}

Closing a File in c

It is very important to close an opened file. If not done properly, file content may gets corrupted.

Syntax

fclose(file_pointer_variable);

Example

#include<stdio.h>
#include<stdlib.h>

void main()
{
  
    FILE* fileptr;
    fileptr = fopen("myfile.txt", "a"); 
    fputc("x", fileptr);

    fclose(fileptr); // Close an open file
}