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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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GETDELIM(3P) POSIX Programmer's Manual GETDELIM(3P)
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.
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>
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().
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.
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:
EOVERFLOW
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.
#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)
exit(1);
while ((read = getline(&line, &len, fp)) != -1) {
printf("Retrieved line of length %zu :\n", read);
printf("%s", line);
}
if (ferror(fp)) {
/* handle error */
}
free(line);
fclose(fp);
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.
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.
None.
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)
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
http://www.opengroup.org/unix/online.html .
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
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 GETDELIM(3P)
Pages that refer to this page: stdio.h(0p), fgets(3p), getline(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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