Manual Pages  — FGETLN

fgetln – get a line from a stream

LIBRARY SYNOPSIS DESCRIPTION RETURN VALUES ERRORS SEE ALSO HISTORY CAVEATS

Standard C Library (libc, -lc)

#include <stdio.h>

char *
fgetln(FILE *stream, size_t *len);

The fgetln() function returns a pointer to the next line from the stream referenced by stream. This line is not a C string as it does not end with a terminating NUL character. The length of the line, including the final newline, is stored in the memory location to which len points. (Note, however, that if the line is the last in a file that does not end in a newline, the returned text will not contain a newline.)

The fgetln() function first appeared in BSD 4.4 .

Since the returned buffer is not a C string (it is not NUL terminated), a common practice is to replace the newline character with '\0'. However, if the last line in a file does not contain a newline, the returned text won't contain a newline either. The following code demonstrates how to deal with this problem by allocating a temporary buffer:

        char *buf, *lbuf;
        size_t len;

        lbuf = NULL;
        while ((buf = fgetln(fp, &len)) != NULL) {
                if (buf[len - 1] == '\n')
                        buf[len - 1] = '\0';
                else {
                        /* EOF without EOL, copy and add the NUL */
                        if ((lbuf = malloc(len + 1)) == NULL)
                                err(1, NULL);
                        memcpy(lbuf, buf, len);
                        lbuf[len] = '\0';
                        buf = lbuf;
                }
                printf("%s\n", buf);
        }
        free(lbuf);
        if (ferror(fp))
                err(1, "fgetln");