C Program to Read Content of a File

Reading a file in C involves opening the file, retrieving its contents, and closing it after use. The C Standard Library provides several functions for reading files depending on the type and format of the data.

• Supports reading text as well as binary files.
• Different functions are available for different reading requirements.

Example: The following program reads and displays the contents of a text file.

#include <stdio.h>

int main()
{
    FILE *fp = fopen("file.txt", "r");
    char ch;

    if (fp == NULL) {
        printf("Unable to open file.");
        return 1;
    }

    while ((ch = fgetc(fp)) != EOF)
        putchar(ch);

    fclose(fp);

    return 0;
}

Output

GeeksforGeeks

Explanation: The program opens the file in read mode, reads one character at a time using fgetc(), displays it, and finally closes the file.

Steps to Read a File in C

Reading a file generally involves the following steps:

1. Open the File

Use the fopen() function in read mode ("r") to open the file.

FILE *fp = fopen("file.txt", "r");

2. Read the Data

Read the file using one of the available input functions.

• fgetc() - Reads one character.
• fgets() - Reads one line.
• fscanf() - Reads formatted data.
• fread() - Reads binary data.

3. Close the File

After reading is complete, close the file using fclose().

fclose(fp);

Methods to Read a File in C

C provides several functions for reading data from a file.

Assume that the file.txt (file to read) contains the following data:

1. Reading a File Using fgetc()

The fgetc() function reads one character at a time from a file. It returns the next character on success and EOF when the end of the file is reached.

Use it when:

• Reading files character by character.
• Processing text one character at a time.
• Counting or filtering specific characters.

Syntax

int fgetc(FILE *stream);

#include <stdio.h>

int main()
{
    FILE *fp = fopen("file.txt", "r");
    char ch;

    if (fp == NULL) {
        printf("Unable to open file.");
        return 1;
    }

    while ((ch = fgetc(fp)) != EOF)
        putchar(ch);

    fclose(fp);

    return 0;
}

Output

GeeksforGeeks

Explanation: The program reads one character at a time until fgetc() returns EOF, indicating the end of the file.

2. Reading a File Using fgets()

The fgets() function reads one line (or a specified number of characters) from a file and stores it in a character array.

Use it when:

• Reading a text file line by line.
• Processing strings that may contain spaces.
• Working with configuration files or log files.

Syntax

char *fgets(char *str, int size, FILE *stream);

#include <stdio.h>

int main()
{
    FILE *fp = fopen("file.txt", "r");
    char buffer[100];

    if (fp == NULL) {
        printf("Unable to open file.");
        return 1;
    }

    while (fgets(buffer, sizeof(buffer), fp))
        printf("%s", buffer);

    fclose(fp);

    return 0;
}

Output

GeeksforGeeks

Explanation: The program reads one line at a time into the buffer and prints it until fgets() returns NULL.

3. Reading a File Using fscanf()

The fscanf() function reads formatted input from a file. It is useful for reading structured data such as numbers, strings, or records stored in a specific format.

Use it when:

• Reading formatted text data.
• Extracting values into variables.
• Processing files containing structured records.

Syntax

int fscanf(FILE *stream, const char *format, ...);

Example

Suppose file.txt contains:

#include <stdio.h>

int main()
{
    FILE *fp = fopen("file.txt", "r");

    char name[50];
    int age;

    if (fp == NULL) {
        printf("Unable to open file.");
        return 1;
    }

    while (fscanf(fp, "%s %d", name, &age) == 2)
        printf("Name: %s  Age: %d\n", name, age);

    fclose(fp);

    return 0;
}

Output

Name: Raman  Age: 12
Name: Kunal  Age: 25
Name: Vikas  Age: 6

Explanation: The program reads a string and an integer from each line according to the specified format and stores them in variables.

4. Reading a File Using fread()

The fread() function reads blocks of binary data from a file into memory. It is commonly used for reading structures, arrays, and other binary data.

Use it when:

• Reading binary files.
• Loading structures or arrays from a file.
• Processing large blocks of data efficiently.

Syntax

size_t fread(void *ptr, size_t size, size_t count, FILE *stream);

#include <stdio.h>

struct Student {
    int roll;
    char name[30];
};

int main()
{
    FILE *fp = fopen("student.dat", "rb");
    struct Stude#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct Course {
     int price;
    char cname[100];
};

int main() {

    // Open binary file in read  mode
  	FILE *ptr = fopen("file.bin", "rb");
  
  	// Structure variable to
  	// store the  file data
    struct Course fileData;
  
 	// Start reading the data using fread
    while (fread(&fileData, sizeof(struct 
                 Course), 1, ptr)) {
        printf("Course Name = %s Price = %d\n", 
            fileData.cname, fileData.price);
    }
    
  	fclose(ptr);
  	return 0;
}nt s;

    if (fp == NULL) {
        printf("Unable to open file.");
        return 1;
    }

    while (fread(&s, sizeof(struct Student), 1, fp))
        printf("%d %s\n", s.roll, s.name);

    fclose(fp);

    return 0;
}

Output

Course Name = Data Structures and Algorithms - Self Paced Price = 6000

The binary file could look like this: