fputc man page


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.

fputc — put a byte on a stream


#include <stdio.h>

int fputc(int c, FILE *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 fputc() function shall write 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 shall advance the indicator appropriately. If the file cannot support positioning requests, or if the stream was opened with append mode, the byte shall be appended to the output stream.

The last data modification and last file status change timestamps of the file shall 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().

Return Value

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


The fputc() function shall 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 thread 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.
An attempt was made to write to a file that exceeds the file size limit of the process.
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 calling thread is not blocking SIGTTOU, the process is not ignoring SIGTTOU, and the process group of the process is orphaned. This error may also be returned under implementation-defined 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 shall also be sent to the thread.

The fputc() function may fail if:

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

The following sections are informative.

See Also

Section 2.5, Standard I/O Streams, ferror(), fopen(), getrlimit(), putc(), puts(), setbuf(), ulimit()

The Base Definitions volume of POSIX.1‐2008, <stdio.h>