Reading lines with fgets in C

fgets is the safe line reader: it takes a size and always terminates.

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

int count_lines(FILE *f) {
    char line[256];
    int lines = 0;

    while (fgets(line, (int) sizeof line, f) != NULL) {
        size_t n = strlen(line);
        if (n > 0 && line[n - 1] == '\n') {
            line[n - 1] = '\0';
        }
        lines++;
    }
    return lines;
}

How it works

1. It keeps the newline, so strip it yourself.
2. A full buffer with no newline means the line was longer.
3. It returns NULL at end of file or on error.

Keywords and builtins used here

• FILE
• NULL
• char
• count_lines
• if
• int
• return
• size_t
• sizeof
• while

The run, in numbers

Lines

16

Characters to type

260

Tokens

93

Three-star pace

95 tpm

At the three-star pace of 95 tokens a minute, this run takes about 59 seconds.

Type this snippet

Step 2 of 4 in Opening & reading, step 2 of 12 in Files & I/O.

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