fgets — Safe String Input in C

C in 100 Seconds, Episode 13

---

scanf stops at whitespace and has no buffer protection. fgets solves both problems — it reads a full line and respects a size limit.

Reading a Line

char line[20];
fgets(line, sizeof(line), stdin);

Three arguments:
1. Buffer — where to store the input
2. Size — maximum characters to read (including the null terminator)
3. Stream — stdin for keyboard input

If the user types more than 19 characters, fgets stops at 19 and adds a \0. No overflow.

The Newline Problem

fgets includes the newline character when the user hits Enter. You usually want to strip it:

line[strcspn(line, "\n")] = 0;

strcspn finds the position of the first \n in the string. Setting that character to 0 (the null terminator) effectively removes the newline.

Seeing the Result

printf("You said: [%s]\n", line);
printf("Length: %lu\n", strlen(line));

The brackets make it easy to see exactly what was captured, including any trailing spaces.

Why fgets Over scanf?

• Buffer safety — you specify a maximum size
• Full lines — spaces are included in the input
• Predictable — no leftover characters in the input buffer

For any real application that reads text from users, fgets is the standard approach.

Full Code

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

int main() {
  char line[20];

  printf("Enter a sentence: ");
  fgets(line, sizeof(line), stdin);

  line[strcspn(line, "\n")] = 0;

  printf("You said: [%s]\n", line);
  printf("Length: %lu\n", strlen(line));

  return 0;
}

Compile and Run

gcc fgets.c -o fgets
./fgets

---

Next episode: Constants and Macros — values that never change.

Student code: github.com/GoCelesteAI/c-in-100-seconds/episode13