fgets() in C: A Beginner’s Tutorial

Reading input safely is an essential part of C programming. While functions like gets() exist, they can be dangerous because they don’t check the buffer size. The safer alternative is fgets(), which allows you to read strings from the user or a file safely.

In this tutorial, you’ll learn how fgets() works, its syntax, examples, and outputs.

What is fgets()?

fgets() is a standard function in <stdio.h> used to read lines of text into a string. It stops reading when:

1. A newline character (\n) is encountered.
2. The specified number of characters has been read.
3. The end-of-file (EOF) is reached.

Because you can specify the buffer size, it prevents buffer overflow—something gets() cannot do.

Syntax

// Syntax of fgets() in C
char *fgets(char *str, int n, FILE *stream);

Parameters:

• str: Array to store the input.
• n: Maximum number of characters to read (including \0).
• stream: Input source (stdin for keyboard or a file pointer).

Return Value:

• Returns str if successful.
• Returns NULL if an error occurs or EOF is reached.

Example 1: Reading Input from the User

// Example: Reading input using fgets()
#include <stdio.h>

int main() {
    char name[50];

    printf("Enter your name: ");

    fgets(name, sizeof(name), stdin);

    printf("Hello, %s", name);

    return 0;
}

Sample Output 1:

Explanation:

• fgets() reads up to 49 characters and adds a null terminator.
• If the input is shorter than the buffer, it stops at the newline.

Example 2: Removing the Newline Character

fgets() keeps the newline (\n) if the user presses Enter. To remove it:

// Example: fgets() with newline removal
#include <stdio.h>
#include <string.h>

int main() {
    char name[50];

    printf("Enter your name: ");
    fgets(name, sizeof(name), stdin);

    // Remove newline character if present
    name[strcspn(name, "\n")] = '\0';

    printf("Hello, %s", name);

    return 0;
}

Sample Output 2:

Explanation:

• strcspn(name, “\n”) finds the newline position and replaces it with \0.
• The string is now clean for printing or comparisons.

Example 3: Reading a Limited Number of Characters

// Example: fgets() with limited buffer size
#include <stdio.h>

int main() {
    char buffer[10];

    printf("Enter a string: ");
    fgets(buffer, sizeof(buffer), stdin);

    printf("You entered: %s", buffer);

    return 0;
}

Sample Output 3:

Explanation:

• The buffer size is 10, so fgets() reads 9 characters and adds the null terminator.
• The newline character is included if space allows.

Example 4: Reading from a File

// Example: fgets() reading from a file
#include <stdio.h>

int main() {

    FILE *file = fopen("example.txt", "r");
    char line[50];

    if(file) {
        while(fgets(line, sizeof(line), file)) {
            printf("%s", line);
        }
        fclose(file);
    } else {
        printf("Could not open the file.\n");
    }

    return 0;
}

Assume example.txt contains:

Hello World

C programming is fun

fgets() is safe

Sample Output 4:

Explanation:

• Reads one line at a time, up to the buffer size.
• Safe and avoids buffer overflow when reading files.

gets() vs fgets()

Tips for Using fgets()

1. Use a large enough buffer for input.
2. Remove the newline if needed.
3. Don’t mix fgets() with scanf() carelessly; leftover input can cause issues.
4. Use it for file reading to safely read line by line.

Also Read: How to get the length of a string in python

Summary

fgets() is a safe, reliable, and flexible way to read strings in C. It works for both keyboard input and file reading, preventing common mistakes like buffer overflow.

By practicing with fgets(), you’ll be able to handle user input safely and write more robust C programs.

Perguntas frequentes