C program to read a file and display its contents

C Programming Language File Input/Output (Article) File Input/Output (Program)

Required knowledge

Basic Input Output, Do while loop, While loop, Pointers, File Handling

In the previous post, I explained how to use FILE pointer, fopen(), fputs() and fclose() function to create and write data into file.

In this post, we will continue further and will learn various functions in C programming to read and display file contents on console.

How to read data from a file?

C programming supports four predefined functions fgetc(), fgets(), fscanf() and fread() to read data from file. These functions are defined in stdio.h header file.

fgetc() - Used to read single character from file.
fgets() - Used to read string from file.
fscanf() - Use this to read formatted input from file.
fread() - Read block of raw bytes from file. Used to read binary files.

Step by step descriptive logic to read a file and display file contents.

• Open a file using fopen() function and store its reference in a FILE pointer say fPtr.
  

  You must open file in r(read) mode or atleast mode that support read access.

• Read content from file using any of these functions fgetc(), fgets(), fscanf() or fread().
• Finally, close the file using fclose(fPtr).

In this post I will explain how to read a file using fgetc() and fgets(). I will explain separately how to read formatted input and binary files.

How to read a file character by character using fgetc()?

int fgetc(FILE * stream);

• The function accepts pointer to FILE type, source stream to read.
• On each successful read it return character (ASCII value) read from stream and advance read position to next character.

  It returns a constant EOF (-1) on unsuccessful read or if there is no more content to read.

Suppose data/file1.txt contains

Hurray!!! I learned to create file in C programming. I also learned to write contents to file. Next, I will learn to read contents from file on Codeforwin. Happy coding ;)

Program:

/**
 * C program to read a file and display file contents character by character using fgetc() 
 */

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


int main()
{
    /* File pointer to hold reference to our file */
    FILE * fPtr;

    char ch;


    /* 
     * Open file in r (read) mode. 
     * "data/file1.txt" is complete file path to read
     */
    fPtr = fopen("data/file1.txt", "r");


    /* fopen() return NULL if last operation was unsuccessful */
    if(fPtr == NULL)
    {
        /* Unable to open file hence exit */
        printf("Unable to open file.\n");
        printf("Please check whether file exists and you have read privilege.\n");
        exit(EXIT_FAILURE);
    }


    /* File open success message */
    printf("File opened successfully. Reading file contents character by character. \n\n");

    do 
    {
        /* Read single character from file */
        ch = fgetc(fPtr);

        /* Print character read on console */
        putchar(ch);

    } while(ch != EOF); /* Repeat this if last read character is not EOF */


    /* Done with this file, close file to release resource */
    fclose(fPtr);


    return 0;
}

Output:

File opened successfully. Reading file contents character by character.

Hurray!!! I learned to create file in C programming. I also learned to write contents to file. Next, I will learn to read contents from file on Codeforwin. Happy coding ;)

Explanation:

Reading a file line by line.
--------------------------------------------
I love programming in C.
Learning programming on Codeforwin is easy.

/**
 * C program to read a file and display file contents line by line using fgets()
 */

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

#define BUFFER_SIZE 1000


int main()
{
    /* File pointer to hold reference to our file */
    FILE * fPtr;

    char buffer[BUFFER_SIZE];
    int totalRead = 0;


    /* 
     * Open file in r (read) mode. 
     * "data/file2.txt" is complete file path to read
     */
    fPtr = fopen("data/file2.txt", "r");


    /* fopen() return NULL if last operation was unsuccessful */
    if(fPtr == NULL)
    {
        /* Unable to open file hence exit */
        printf("Unable to open file.\n");
        printf("Please check whether file exists and you have read privilege.\n");
        exit(EXIT_FAILURE);
    }


    /* File open success message */
    printf("File opened successfully. Reading file contents line by line. \n\n");


    /* Repeat this until read line is not NULL */
    while(fgets(buffer, BUFFER_SIZE, fPtr) != NULL) 
    {
        /* Total character read count */
        totalRead = strlen(buffer);


        /*
         * Trim new line character from last if exists.
         */
        buffer[totalRead - 1] = buffer[totalRead - 1] == '\n' 
                                    ? '\0' 
                                    : buffer[totalRead - 1];


        /* Print line read on cosole*/
        printf("%s\n", buffer);

    } 


    /* Done with this file, close file to release resource */
    fclose(fPtr);


    return 0;
}

File opened successfully. Reading file contents line by line.

Reading a file line by line.
--------------------------------------------
I love programming in C.
Learning programming on Codeforwin is easy.