getdelim(3p) — Linux manual page


GETDELIM(3P)            POSIX Programmer's Manual           GETDELIM(3P)

PROLOG         top

       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.

NAME         top

       getdelim, getline — read a delimited record from stream

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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.

       If *lineptr is a null pointer or if the object pointed to by
       *lineptr is of insufficient size, an object shall be allocated as
       if by malloc() or the object shall be reallocated as if by
       realloc(), respectively, such that the object is large enough to
       hold the characters to be written to it, including the
       terminating NUL, and *n shall be set to the new size. If the
       object was allocated, or if the reallocation operation moved the
       object, *lineptr shall be updated to point to the new object or
       new location.  The characters read, including any delimiter,
       shall be stored in the object, 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>

       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         top

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

ERRORS         top

       For the conditions under which the getdelim() and getline()
       functions shall fail and may fail, refer to fgetc(3p).

       In addition, these functions shall fail if:

       EINVAL lineptr or n is a null pointer.

       ENOMEM Insufficient memory is available.

       These functions may fail if:

              The number of bytes to be written into the buffer,
              including the delimiter character (if encountered), would
              exceed {SSIZE_MAX}.

       The following sections are informative.

EXAMPLES         top

           #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;


       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.

RATIONALE         top

       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         top

       Section 2.5, Standard I/O Streams, fgetc(3p), fgets(3p),
       free(3p), malloc(3p), realloc(3p)

       The Base Definitions volume of POSIX.1‐2017, stdio.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any
       discrepancy between this version and the original IEEE and The
       Open Group Standard, the original IEEE and The Open Group
       Standard is the referee document. The original Standard can be
       obtained online at .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see .

IEEE/The Open Group               2017                      GETDELIM(3P)

Pages that refer to this page: stdio.h(0p)fgets(3p)getline(3p)