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FGETS(3P) POSIX Programmer's Manual FGETS(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.
fgets — get a string from a stream
#include <stdio.h>
char *fgets(char *restrict s, int n, FILE *restrict stream);
The functionality described on this reference page is aligned with
the ISO C standard. Any conflict between the requirements described
here and the ISO C standard is unintentional. This volume of
POSIX.1‐2008 defers to the ISO C standard.
The fgets() function shall read bytes from stream into the array
pointed to by s, until n−1 bytes are read, or a <newline> is read and
transferred to s, or an end-of-file condition is encountered. The
string is then terminated with a null byte.
The fgets() function 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, fgets() shall return s. If the stream is
at end-of-file, the end-of-file indicator for the stream shall be set
and fgets() shall return a null pointer. If a read error occurs, the
error indicator for the stream shall be set, fgets() shall return a
null pointer, and shall set errno to indicate the error.
Refer to fgetc(3p).
The following sections are informative.
Reading Input
The following example uses fgets() to read lines of input. It assumes
that the file it is reading is a text file and that lines in this
text file are no longer than 16384 (or {LINE_MAX} if it is less than
16384 on the implementation where it is running) bytes long. (Note
that the standard utilities have no line length limit if
sysconf(_SC_LINE_MAX) returns −1 without setting errno. This example
assumes that sysconf(_SC_LINE_MAX) will not fail.)
#include <limits.h>
#include <stdio.h>
#include <unistd.h>
#define MYLIMIT 16384
char *line;
int line_max;
if (LINE_MAX >= MYLIMIT) {
// Use maximum line size of MYLIMIT. If LINE_MAX is
// bigger than our limit, sysconf() can't report a
// smaller limit.
line_max = MYLIMIT;
} else {
long limit = sysconf(_SC_LINE_MAX);
line_max = (limit < 0 || limit > MYLIMIT) ? MYLIMIT : (int)limit;
}
// line_max + 1 leaves room for the null byte added by fgets().
line = malloc(line_max + 1);
if (line == NULL) {
// out of space
...
return error;
}
while (fgets(line, line_max + 1, fp) != NULL) {
// Verify that a full line has been read ...
// If not, report an error or prepare to treat the
// next time through the loop as a read of a
// continuation of the current line.
...
// Process line ...
...
}
free(line);
...
None.
None.
None.
Section 2.5, Standard I/O Streams, fgetc(3p), fopen(3p), fread(3p),
fscanf(3p), getc(3p), getchar(3p), getdelim(3p), gets(3p), ungetc(3p)
The Base Definitions volume of POSIX.1‐2008, stdio.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/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 2013 FGETS(3P)
Pages that refer to this page: stdio.h(0p), fgetc(3p), getdelim(3p), gets(3p)