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gets() and puts() in C Programming

Learn string I/O with gets() and puts() in C. Understand why gets() is dangerous and deprecated, buffer overflow vulnerabilities, and safer alternatives like fgets(). Includes practical examples.

The gets() and puts() functions handle string input and output in C. While puts() remains a perfectly valid and useful function, gets() has become one of the most infamous functions in C's history — it was officially removed from the C11 standard because it's inherently unsafe and has been responsible for countless security vulnerabilities. Understanding why it's dangerous and what to use instead is essential knowledge for any C programmer.

puts() — Print a String with Newline

puts() writes a string to standard output and automatically appends a newline character. It's simpler and slightly faster than printf("%s\n", str) for plain string output.

c example

int puts(const char *str);

Returns a non-negative value on success, or EOF on error.

c example

#include <stdio.h>

int main() {
    // Simple string output
    puts("Hello, World!");
    puts("This is C programming.");

    // With variables
    char name[] = "Alice";
    char greeting[] = "Welcome to the course!";

    puts(name);
    puts(greeting);

    // Empty string just prints a newline
    puts("");

    puts("Done!");

    return 0;
}

Output

Hello, World!
This is C programming.
Alice
Welcome to the course!

Done!

puts() vs printf() for Strings

c example

#include <stdio.h>

int main() {
    char msg[] = "Hello";

    // puts() adds newline automatically
    puts(msg);

    // printf() does NOT add newline
    printf("%s", msg);
    printf("\n");

    // printf() can do formatting; puts() cannot
    printf("Name: %s, Age: %d\n", "Bob", 25);

    // puts() is slightly faster for plain strings (no format parsing)
    puts("Just a plain string");

    return 0;
}

Output

Hello
Hello
Name: Bob, Age: 25
Just a plain string

When to use puts():

Printing a complete string on its own line
No formatting needed (no variables mixed in)
Slightly better performance for simple output

gets() — The Dangerous Function

gets() reads a line from standard input (until newline or EOF) and stores it in a buffer. The newline is replaced with a null terminator.

c example

char *gets(char *str); // DEPRECATED AND REMOVED IN C11!

Why gets() is Dangerous

The fatal flaw: gets() has no way to limit input length. If the user enters more characters than the buffer can hold, it overflows into adjacent memory — corrupting data, crashing the program, or enabling code injection attacks.

Example

#include <stdio.h> int main() { char buffer[10]; // Can hold 9 chars + null terminator printf("Enter text: "); gets(buffer); // DANGEROUS! What if user types 50 characters? printf("You entered: %s\n", buffer); return 0; }

If the user enters "This is a very long string that exceeds the buffer", gets() will happily write past the 10-byte buffer, corrupting the stack. This is the classic buffer overflow vulnerability that attackers exploit.

The Morris Worm (1988)

The first major Internet worm exploited a gets() buffer overflow in the fingerd daemon. This historical event highlighted just how dangerous gets() is and eventually led to its removal from the C standard.

fgets() — The Safe Alternative

fgets() is what you should always use instead of gets(). It takes a size parameter that prevents buffer overflow:

c example

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

Reads at most n-1 characters (saves space for null terminator)
Stops at newline (which IS stored in the string, unlike gets())
Returns NULL on error or end-of-file

Example

#include <stdio.h> #include <string.h> int main() { char name[50]; char city[20]; printf("Enter your full name: "); fgets(name, sizeof(name), stdin); // Remove trailing newline if present name[strcspn(name, "\n")] = '\0'; printf("Enter your city: "); fgets(city, sizeof(city), stdin); city[strcspn(city, "\n")] = '\0'; printf("Name: %s, City: %s\n", name, city); return 0; }

Output

Enter your full name: John Smith
Enter your city: New York
Name: John Smith, City: New York

The Newline Issue with fgets()

Unlike gets(), fgets() keeps the newline in the string. You usually want to remove it:

Example

#include <stdio.h> #include <string.h> int main() { char buffer[100]; printf("Enter text: "); fgets(buffer, sizeof(buffer), stdin); printf("With newline: [%s]\n", buffer); printf("Length: %lu\n", strlen(buffer)); // Method 1: Replace newline with null terminator buffer[strcspn(buffer, "\n")] = '\0'; printf("Without newline: [%s]\n", buffer); printf("Length: %lu\n", strlen(buffer)); return 0; }

Output

Enter text: Hello World
With newline: [Hello World
]
Length: 12
Without newline: [Hello World]
Length: 11

Other Ways to Remove the Newline

Example

#include <stdio.h> #include <string.h> int main() { char buf[100]; printf("Enter text: "); fgets(buf, sizeof(buf), stdin); // Method 1: strcspn (safest) buf[strcspn(buf, "\n")] = '\0'; // Method 2: strlen approach // size_t len = strlen(buf); // if (len > 0 && buf[len-1] == '\n') // buf[len-1] = '\0'; // Method 3: strtok // strtok(buf, "\n"); printf("Result: [%s]\n", buf); return 0; }

Comparison: gets() vs fgets() vs scanf()

Feature	gets()	fgets()	scanf("%s")
Buffer overflow protection	❌ No	✅ Yes	⚠️ With width
Reads spaces	✅ Yes	✅ Yes	❌ No
Stores newline	❌ No	✅ Yes	❌ No
Standard in C11	❌ Removed	✅ Yes	✅ Yes
Input source	stdin only	Any FILE*	stdin only
Safety	Dangerous	Safe	Moderate

Example

#include <stdio.h> #include <string.h> int main() { char buf1[50], buf2[50], buf3[50]; // scanf reads only first word (stops at space) printf("scanf (enter 'Hello World'): "); scanf("%49s", buf1); printf("scanf got: [%s]\n", buf1); // Clear buffer while (getchar() != '\n'); // fgets reads full line including spaces printf("fgets (enter 'Hello World'): "); fgets(buf2, sizeof(buf2), stdin); buf2[strcspn(buf2, "\n")] = '\0'; printf("fgets got: [%s]\n", buf2); return 0; }

Output

scanf (enter 'Hello World'): Hello World
scanf got: [Hello]
fgets (enter 'Hello World'): Hello World
fgets got: [Hello World]

Practical Examples with puts() and fgets()

Reading and Displaying Multiple Lines

Example

#include <stdio.h> #include <string.h> int main() { char lines[5][100]; int count = 0; puts("Enter up to 5 lines (empty line to stop):"); for (int i = 0; i < 5; i++) { printf("%d> ", i + 1); fgets(lines[i], sizeof(lines[i]), stdin); lines[i][strcspn(lines[i], "\n")] = '\0'; if (strlen(lines[i]) == 0) break; count++; } puts("\nYou entered:"); for (int i = 0; i < count; i++) { puts(lines[i]); } return 0; }

Output

Enter up to 5 lines (empty line to stop):
1> Hello World
2> C Programming
3> Is Fun

You entered:
Hello World
C Programming
Is Fun

Simple Text Reversal

Example

#include <stdio.h> #include <string.h> int main() { char input[200]; char reversed[200]; puts("Enter a sentence:"); fgets(input, sizeof(input), stdin); input[strcspn(input, "\n")] = '\0'; int len = strlen(input); for (int i = 0; i < len; i++) { reversed[i] = input[len - 1 - i]; } reversed[len] = '\0'; puts("Reversed:"); puts(reversed); return 0; }

Output

Enter a sentence:
Hello World
Reversed:
dlroW olleH

Password Input (Masking with fgets)

Example

#include <stdio.h> #include <string.h> int main() { char username[50]; char password[50]; char correctUser[] = "admin"; char correctPass[] = "secret"; puts("=== Login System ==="); printf("Username: "); fgets(username, sizeof(username), stdin); username[strcspn(username, "\n")] = '\0'; printf("Password: "); fgets(password, sizeof(password), stdin); password[strcspn(password, "\n")] = '\0'; if (strcmp(username, correctUser) == 0 && strcmp(password, correctPass) == 0) { puts("Access granted! Welcome, admin."); } else { puts("Access denied! Invalid credentials."); } return 0; }

Output

=== Login System ===
Username: admin
Password: secret
Access granted! Welcome, admin.

Compiler Warnings for gets()

Modern compilers will warn you (or refuse to compile) when you use gets():

Code example

warning: the `gets' function is dangerous and should not be used.

GCC with -Wall flag will always warn about gets(). Some compilers define gets() as an error in C11 mode.

Interview Questions

Q1: Why was gets() removed from the C11 standard?

gets() was removed because it's inherently unsafe — there's no way to specify buffer size, making buffer overflow inevitable when user input exceeds the buffer. This has led to countless security vulnerabilities including the Morris Worm of 1988. It was deprecated in C99 and officially removed in C11.

Q2: What is the difference between gets() and fgets()?

Three key differences: (1) fgets() takes a size parameter preventing overflow; gets() does not. (2) fgets() retains the newline character in the string; gets() strips it. (3) fgets() can read from any file stream; gets() only reads from stdin.

Q3: Why does fgets() store the newline character?

fgets() keeps the newline so you can distinguish between a line that was fully read (has \n) and a line that was truncated because it exceeded the buffer size (no \n). If the newline is absent, you know more characters remain unread.

Q4: What is the difference between puts() and printf() for string output?

puts() automatically appends a newline and doesn't parse format specifiers — it just outputs the raw string. printf() requires \n explicitly and parses format specifiers (%d, %s, etc.). puts() is slightly faster for plain strings because there's no format string parsing overhead.

Q5: How do you safely remove the newline from fgets() input?

The safest method is: buffer[strcspn(buffer, "\n")] = '\0'; — strcspn() finds the position of the first \n (or returns the string length if none exists), then you replace it with a null terminator. This works correctly even if no newline is present.

Summary

puts() prints a string and adds a newline — simple and fast for string output
gets() is removed from C11 due to buffer overflow vulnerability — never use it
fgets() is the safe replacement: it limits input length and works with any file stream
fgets() keeps the newline — remove it with strcspn() or strlen() method
Always use sizeof(buffer) with fgets() for automatic size calculation
scanf("%s") doesn't read spaces; fgets() reads the entire line including spaces
Modern compilers will warn or error when you try to use gets()

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for gets() and puts() in C Programming.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this C Programming topic.

Search Terms

c-programming, c programming, programming, input, output, gets, and, puts

Continue learning this concept

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C Notes

gets() and puts() in C Programming

Learn string I/O with gets() and puts() in C. Understand why gets() is dangerous and deprecated, buffer overflow vulnerabilities, and safer alternatives like fgets(). Includes practical examples.

puts() — Print a String with Newline

puts() writes a string to standard output and automatically appends a newline character. It's simpler and slightly faster than printf("%s\n", str) for plain string output.

c example

int puts(const char *str);

Returns a non-negative value on success, or EOF on error.

c example

#include <stdio.h>

int main() {
    // Simple string output
    puts("Hello, World!");
    puts("This is C programming.");

    // With variables
    char name[] = "Alice";
    char greeting[] = "Welcome to the course!";

    puts(name);
    puts(greeting);

    // Empty string just prints a newline
    puts("");

    puts("Done!");

    return 0;
}

Output

Hello, World!
This is C programming.
Alice
Welcome to the course!

Done!

puts() vs printf() for Strings

c example

#include <stdio.h>

int main() {
    char msg[] = "Hello";

    // puts() adds newline automatically
    puts(msg);

    // printf() does NOT add newline
    printf("%s", msg);
    printf("\n");

    // printf() can do formatting; puts() cannot
    printf("Name: %s, Age: %d\n", "Bob", 25);

    // puts() is slightly faster for plain strings (no format parsing)
    puts("Just a plain string");

    return 0;
}

Output

Hello
Hello
Name: Bob, Age: 25
Just a plain string

When to use puts():

Printing a complete string on its own line
No formatting needed (no variables mixed in)
Slightly better performance for simple output

gets() — The Dangerous Function

gets() reads a line from standard input (until newline or EOF) and stores it in a buffer. The newline is replaced with a null terminator.

c example

char *gets(char *str); // DEPRECATED AND REMOVED IN C11!

Why gets() is Dangerous

Example

The Morris Worm (1988)

fgets() — The Safe Alternative

fgets() is what you should always use instead of gets(). It takes a size parameter that prevents buffer overflow:

c example

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

Reads at most n-1 characters (saves space for null terminator)
Stops at newline (which IS stored in the string, unlike gets())
Returns NULL on error or end-of-file

Example

Output

Enter your full name: John Smith
Enter your city: New York
Name: John Smith, City: New York

The Newline Issue with fgets()

Unlike gets(), fgets() keeps the newline in the string. You usually want to remove it:

Example

Output

Enter text: Hello World
With newline: [Hello World
]
Length: 12
Without newline: [Hello World]
Length: 11

Other Ways to Remove the Newline

Example

Comparison: gets() vs fgets() vs scanf()

Feature	gets()	fgets()	scanf("%s")
Buffer overflow protection	❌ No	✅ Yes	⚠️ With width
Reads spaces	✅ Yes	✅ Yes	❌ No
Stores newline	❌ No	✅ Yes	❌ No
Standard in C11	❌ Removed	✅ Yes	✅ Yes
Input source	stdin only	Any FILE*	stdin only
Safety	Dangerous	Safe	Moderate

Example

Output

scanf (enter 'Hello World'): Hello World
scanf got: [Hello]
fgets (enter 'Hello World'): Hello World
fgets got: [Hello World]

Practical Examples with puts() and fgets()

Reading and Displaying Multiple Lines

Example

Output

Enter up to 5 lines (empty line to stop):
1> Hello World
2> C Programming
3> Is Fun

You entered:
Hello World
C Programming
Is Fun

Simple Text Reversal

Example

Output

Enter a sentence:
Hello World
Reversed:
dlroW olleH

Password Input (Masking with fgets)

Example

Output

=== Login System ===
Username: admin
Password: secret
Access granted! Welcome, admin.

Compiler Warnings for gets()

Modern compilers will warn you (or refuse to compile) when you use gets():

Code example

warning: the `gets' function is dangerous and should not be used.

GCC with -Wall flag will always warn about gets(). Some compilers define gets() as an error in C11 mode.

Interview Questions

Q1: Why was gets() removed from the C11 standard?

Q2: What is the difference between gets() and fgets()?

Q3: Why does fgets() store the newline character?

Q4: What is the difference between puts() and printf() for string output?

Q5: How do you safely remove the newline from fgets() input?

Summary

puts() prints a string and adds a newline — simple and fast for string output
gets() is removed from C11 due to buffer overflow vulnerability — never use it
fgets() is the safe replacement: it limits input length and works with any file stream
fgets() keeps the newline — remove it with strcspn() or strlen() method
Always use sizeof(buffer) with fgets() for automatic size calculation
scanf("%s") doesn't read spaces; fgets() reads the entire line including spaces
Modern compilers will warn or error when you try to use gets()

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for gets() and puts() in C Programming.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this C Programming topic.

Search Terms

c-programming, c programming, programming, input, output, gets, and, puts

Continue learning this concept

Previousgetchar() and putchar() in C Programming NextC Input Output Programs and Examples