getdelim man page


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

getdelim, getline — read a delimited record from stream


#include <stdio.h>

ssize_t getdelim(char **restrict lineptr, size_t *restrict n,
    int delimiter, FILE *restrict stream);
ssize_t getline(char **restrict lineptr, size_t *restrict n,
    FILE *restrict stream);


The getdelim() function shall read from stream until it encounters a character matching the delimiter character. The delimiter argument is an int, the value of which the application shall ensure is a character representable as an unsigned char of equal value that terminates the read process. If the delimiter argument has any other value, the behavior is undefined.

The application shall ensure that *lineptr is a valid argument that could be passed to the free() function. If *n is non-zero, the application shall ensure that *lineptr either points to an object of size at least *n bytes, or is a null pointer.

The size of the object pointed to by *lineptr shall be increased to fit the incoming line, if it isn't already large enough, including room for the delimiter and a terminating NUL. The characters read, including any delimiter, shall be stored in the string pointed to by the lineptr argument, and a terminating NUL added when the delimiter or end of file is encountered.

The getline() function shall be equivalent to the getdelim() function with the delimiter character equal to the <newline> character.

The getdelim() and getline() functions may mark the last data access timestamp of the file associated with stream for update. The last data access timestamp shall be marked for update by the first successful execution of fgetc(), fgets(), fread(), fscanf(), getc(), getchar(), getdelim(), getline(), gets(), or scanf() using stream that returns data not supplied by a prior call to ungetc().

Return Value

Upon successful completion, the getline() and getdelim() functions shall return the number of characters written into the buffer, including the delimiter character if one was encountered before EOF, but excluding the terminating NUL character. If no characters were read, and the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-of-file indicator for the stream shall be set and the function shall return -1. If an error occurs, the error indicator for the stream shall be set, and the function shall return -1 and set errno to indicate the error.


For the conditions under which the getdelim() and getline() functions shall fail and may fail, refer to fgetc().

In addition, these functions shall fail if:

lineptr or n is a null pointer.
Insufficient memory is available.

These functions may fail if:

More than {SSIZE_MAX} characters were read without encountering the delimiter character.

The following sections are informative.


#include <stdio.h>
#include <stdlib.h>

int main(void)
    FILE *fp;
    char *line = NULL;
    size_t len = 0;
    ssize_t read;
    fp = fopen("/etc/motd", "r");
    if (fp == NULL)
    while ((read = getline(&line, &len, fp)) != -1) {
        printf("Retrieved line of length %zu :\n", read);
        printf("%s", line);
    if (ferror(fp)) {
        /* handle error */
    return 0;

Application Usage

Setting *lineptr to a null pointer and *n to zero are allowed and a recommended way to start parsing a file.

The ferror() or feof() functions should be used to distinguish between an error condition and an end-of-file condition.

Although a NUL terminator is always supplied after the line, note that strlen(*lineptr) will be smaller than the return value if the line contains embedded NUL characters.


These functions are widely used to solve the problem that the fgets() function has with long lines. The functions automatically enlarge the target buffers if needed. These are especially useful since they reduce code needed for applications.

See Also

Section 2.5, Standard I/O Streams, fgetc(), fgets(), free()

The Base Definitions volume of POSIX.1‐2008, <stdio.h>