fgets and fputs

Learn to read and write lines with fgets and fputs.

fgets and fputs

fgets and fputs are the basic way to read and write lines to/from a file. fgets includes the newline character; fputs doesn't add an automatic newline.

Example: fputs("Merhaba\n", f); writes a line to the file. char line[64]; fgets(line, sizeof(line), f); reads a line from the file. The second parameter of fgets is the maximum bytes to read; this prevents overflow. fgets returns NULL at end of file; this feature is used to read all lines with a loop.

EOF and NULL

fgets returns NULL at end of file. This feature is used to read all lines with a loop. The NULL check is the loop's stop condition.

Example: while (fgets(line, sizeof(line), f) != NULL) { printf("%s", line); }. This loop prints every line of the file to the screen. Because fgets includes the newline, printf doesn't add an extra \n. This pattern is standard for processing text files; log files, configuration files and reports are read this way.

Exercise Write a line, read back and print

Open with FILE *f = fopen("line.txt", "w"); (check NULL). Write with fputs("Merhaba dünya\n", f);, fclose(f);. Reopen with f = fopen("line.txt", "r");. Declare char line[64];; read with fgets(line, sizeof(line), f);. fclose(f);. Print with printf("%s", line);.

Show example solution

#include <stdio.h>

int main(void) {
    FILE *f = fopen("line.txt", "w");
    if (f == NULL) return 1;
    fputs("Merhaba dünya\n", f);
    fclose(f);

    f = fopen("line.txt", "r");
    if (f == NULL) return 1;
    char line[64];
    fgets(line, sizeof(line), f);
    fclose(f);

    printf("%s", line);
    return 0;
}

Test yourself

Complete the fgets call

fgets(line, ____, f);

Show answer

fgets(line, sizeof(line), f);

Match functions to purpose

fgets

Line read
fputs

String write
sizeof(line)

Size limit
NULL

EOF indicator
What does fgets return at end of file?
- -1
- 0
- NULL
- EOF
Show answer

NULL — fgets returns NULL at EOF; this is used as a loop condition.

Next lesson: fclose

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