getline(3) — Linux manual page


getline(3)              Library Functions Manual              getline(3)

NAME         top

       getline, getdelim - delimited string input

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <stdio.h>

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

   Feature Test Macro Requirements for glibc (see

       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

       If *lineptr is set to NULL 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

       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 a failure, errno is set
       to indicate the error.

       If *lineptr was set to NULL before the call, then the buffer
       should be freed by the user program even on failure.

ERRORS         top

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

       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 │

STANDARDS         top


HISTORY         top

       GNU, 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 %zd:\n", nread);
               fwrite(line, nread, 1, stdout);


SEE ALSO         top

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

COLOPHON         top

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Linux man-pages 6.9.1          2024-06-15                     getline(3)

Pages that refer to this page: fgetc(3)gets(3)rpmatch(3)scanf(3)