Section: POSIX Programmer's Manual (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.
--- put a string on a stream
int fputs(const char *restrict s, 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.1-2017 defers to the ISO C standard.
function shall write the null-terminated string pointed to by
to the stream pointed to by
The terminating null byte shall not be written.
The last data modification and last file status change timestamps
of the file shall be marked for update between the successful
and the next successful completion of a call to
on the same stream or a call to
Upon successful completion,
shall return a non-negative number. Otherwise, it shall return EOF,
set an error indicator for the stream,
to indicate the error.
The following sections are informative.
Printing to Standard Output
The following example gets the current time, converts it to a string
and prints it to standard output using
It then prints the number of minutes to an event for which it is
printf("The time is ");
printf("There are still %d minutes to the event.\n",
function appends a
This volume of POSIX.1-2017 requires that successful completion simply return a non-negative
integer. There are at least three known different implementation
conventions for this requirement:
Return a constant value.
Return the last character written.
Return the number of bytes written. Note that this implementation
convention cannot be adhered to for strings longer than
bytes as the value would not be representable in the return type of the
function. For backwards-compatibility, implementations can return the
number of bytes for strings of up to
bytes, and return
for all longer strings.
function is one whose source code was specified in the referenced The C Programming Language
. In the
original edition, the function had no defined return value, yet many
practical implementations would, as a side-effect, return the value of the
last character written as that was the value remaining in the accumulator
used as a return value. In the second edition of the book, either the
fixed value 0 or EOF would be returned depending upon the return value of
however, for compatibility with extant implementations, several
implementations would, upon success, return a positive value representing
the last byte written.
, Standard I/O Streams,
The Base Definitions volume of POSIX.1-2017,
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
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