getline(3) — Linux manual page


GETLINE(3)                Linux Programmer's Manual               GETLINE(3)

NAME         top

       getline, getdelim - delimited string input

SYNOPSIS         top

       #include <stdio.h>

       ssize_t getline(char **lineptr, size_t *n, FILE *stream);

       ssize_t getdelim(char **lineptr, size_t *n, int delim, FILE *stream);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getline(), getdelim():
           Since glibc 2.10:
               _POSIX_C_SOURCE >= 200809L
           Before glibc 2.10:

DESCRIPTION         top

       getline() reads an entire line from stream, storing the address of
       the buffer containing the text into *lineptr.  The buffer is null-
       terminated and includes the newline character, if one was found.

       If *lineptr is set to NULL and *n is set 0 before the call, then
       getline() will allocate a buffer for storing the line.  This buffer
       should be freed by the user program even if getline() failed.

       Alternatively, before calling getline(), *lineptr can contain a
       pointer to a malloc(3)-allocated buffer *n bytes in size.  If the
       buffer is not large enough to hold the line, getline() resizes it
       with realloc(3), updating *lineptr and *n as necessary.

       In either case, on a successful call, *lineptr and *n will be updated
       to reflect the buffer address and allocated size respectively.

       getdelim() works like getline(), except that a line delimiter other
       than newline can be specified as the delimiter argument.  As with
       getline(), a delimiter character is not added if one was not present
       in the input before end of file was reached.

RETURN VALUE         top

       On success, getline() and getdelim() return the number of characters
       read, including the delimiter character, but not including the
       terminating null byte ('\0').  This value can be used to handle
       embedded null bytes in the line read.

       Both functions return -1 on failure to read a line (including end-of-
       file condition).  In the event of an error, errno is set to indicate
       the cause.

ERRORS         top

       EINVAL Bad arguments (n or lineptr is NULL, or stream is not valid).

       ENOMEM Allocation or reallocation of the line buffer failed.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface             Attribute     Value   │
       │getline(), getdelim() │ Thread safety │ MT-Safe │

CONFORMING TO         top

       Both getline() and getdelim() were originally GNU extensions.  They
       were standardized in POSIX.1-2008.

EXAMPLES         top

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

       main(int argc, char *argv[])
           FILE *stream;
           char *line = NULL;
           size_t len = 0;
           ssize_t nread;

           if (argc != 2) {
               fprintf(stderr, "Usage: %s <file>\n", argv[0]);

           stream = fopen(argv[1], "r");
           if (stream == NULL) {

           while ((nread = getline(&line, &len, stream)) != -1) {
               printf("Retrieved line of length %zu:\n", nread);
               fwrite(line, nread, 1, stdout);


SEE ALSO         top

       read(2), fgets(3), fopen(3), fread(3), scanf(3)

COLOPHON         top

       This page is part of release 5.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

GNU                              2020-06-09                       GETLINE(3)

Pages that refer to this page: fgetc(3)fgets(3)getc(3)getchar(3)gets(3)rpmatch(3)ungetc(3)