getline(3) - Linux manual page (original) (raw)

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 feature_test_macros(7)):

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

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 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)](../man3/malloc.3.html)-allocated buffer _*n_ bytes in size.  If the
   buffer is not large enough to hold the line, **getline**() resizes it
   with [realloc(3)](../man3/realloc.3.html), 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.

   At end of file, both functions return -1 with the file stream end-
   of-file indicator set.  On error, both functions return -1 with
   the file stream error indicator set, and _[errno](../man3/errno.3.html)_ 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
          valid).

   **ENOMEM** Allocation or reallocation of the line buffer failed.

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────────────────┼───────────────┼─────────┤
   │ **getline**(), **getdelim**()                │ Thread safety │ MT-Safe │
   └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

   POSIX.1-2008.

HISTORY top

   GNU, POSIX.1-2008.

EXAMPLES top

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

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

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

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

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

       free(line);
       fclose(stream);
       exit(EXIT_SUCCESS);
   }

SEE ALSO top

   [read(2)](../man2/read.2.html), [fgets(3)](../man3/fgets.3.html), [fopen(3)](../man3/fopen.3.html), [fread(3)](../man3/fread.3.html), [scanf(3)](../man3/scanf.3.html)

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Linux man-pages 6.10 2024-12-20 getline(3)

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