The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group


fputc - put a byte on a stream


#include <stdio.h>

int fputc(int c, FILE *stream);


The fputc() function writes the byte specified by c (converted to an unsigned char) to the output stream pointed to by stream, at the position indicated by the associated file-position indicator for the stream (if defined), and advances the indicator appropriately. If the file cannot support positioning requests, or if the stream was opened with append mode, the byte is appended to the output stream.

The st_ctime and st_mtime fields of the file will be marked for update between the successful execution of fputc() and the next successful completion of a call to fflush() or fclose() on the same stream or a call to exit() or abort().


Upon successful completion, fputc() returns the value it has written. Otherwise, it returns EOF, the error indicator for the stream is set, and errno is set to indicate the error.


The fputc() function will fail if either the stream is unbuffered or the stream's buffer needs to be flushed, and:
The O_NONBLOCK flag is set for the file descriptor underlying stream and the process would be delayed in the write operation.
The file descriptor underlying stream is not a valid file descriptor open for writing.
An attempt was made to write to a file that exceeds the maximum file size  or the process' file size limit.
The file is a regular file and an attempt was made to write at or beyond the offset maximum.
The write operation was terminated due to the receipt of a signal, and no data was transferred.
A physical I/O error has occurred, or  the process is a member of a background process group attempting to write to its controlling terminal, TOSTOP is set, the process is neither ignoring nor blocking SIGTTOU and the process group of the process is orphaned. This error may also be returned under implementation-dependent conditions.
There was no free space remaining on the device containing the file.
An attempt is made to write to a pipe or FIFO that is not open for reading by any process. A SIGPIPE signal will also be sent to the thread.

The fputc() function may fail if:

Insufficient storage space is available.
A request was made of a non-existent device, or the request was outside the capabilities of the device.








ferror(), fopen(), getrlimit(), putc(), puts(), setbuf(), ulimit(), <stdio.h>.


Derived from Issue 1 of the SVID.

UNIX ® is a registered Trademark of The Open Group.
Copyright © 1997 The Open Group
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