The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group


fsetpos - set current file position


#include <stdio.h>

int fsetpos(FILE *
stream, const fpos_t *pos);


[CX] [Option Start] 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. [Option End]

The fsetpos() function shall set the file position and state indicators for the stream pointed to by stream according to the value of the object pointed to by pos, which the application shall ensure is a value obtained from an earlier call to fgetpos() on the same stream. If a read or write error occurs, the error indicator for the stream shall be set and fsetpos() fails.

A successful call to the fsetpos() function shall clear the end-of-file indicator for the stream and undo any effects of ungetc() on the same stream. After an fsetpos() call, the next operation on an update stream may be either input or output.

[CX] [Option Start] The behavior of fsetpos() on devices which are incapable of seeking is implementation-defined. The value of the file offset associated with such a device is undefined. [Option End]

The fsetpos() function shall not change the setting of errno if successful.


The fsetpos() function shall return 0 if it succeeds; otherwise, it shall return a non-zero value and set errno to indicate the error.


The fsetpos() function shall fail if, [CX] [Option Start]  either the stream is unbuffered or the stream's buffer needed to be flushed, and the call to fsetpos() causes an underlying lseek() or write() to be invoked, and: [Option End]

[CX] [Option Start] The O_NONBLOCK flag is set for the file descriptor and the thread would be delayed in the write operation. [Option End]
[CX] [Option Start] The file descriptor underlying the stream file is not open for writing or the stream's buffer needed to be flushed and the file is not open. [Option End]
[CX] [Option Start] An attempt was made to write a file that exceeds the maximum file size. [Option End]
[XSI] [Option Start] An attempt was made to write a file that exceeds the file size limit of the process. [Option End]
[CX] [Option Start] The file is a regular file and an attempt was made to write at or beyond the offset maximum associated with the corresponding stream. [Option End]
[CX] [Option Start] The write operation was terminated due to the receipt of a signal, and no data was transferred. [Option End]
[CX] [Option Start] A physical I/O error has occurred, or the process is a member of a background process group attempting to perform a 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. [Option End]
[CX] [Option Start] There was no free space remaining on the device containing the file. [Option End]
[CX] [Option Start] An attempt was 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. [Option End]
[CX] [Option Start] The file descriptor underlying stream is associated with a pipe, FIFO, or socket. [Option End]

The fsetpos() function may fail if:

[CX] [Option Start] A request was made of a nonexistent device, or the request was outside the capabilities of the device. [Option End]

The following sections are informative.










Standard I/O Streams, fopen, ftell, lseek, rewind, ungetc, write

XBD <stdio.h>


First released in Issue 4. Derived from the ISO C standard.

Issue 6

Extensions beyond the ISO C standard are marked.

The normative text is updated to avoid use of the term "must" for application requirements.

The DESCRIPTION is updated to clarify that the error indicator is set for the stream on a read or write error. This is for alignment with the ISO/IEC 9899:1999 standard.

IEEE Std 1003.1-2001/Cor 1-2002, item XSH/TC1/D6/21 is applied, deleting an erroneous [EINVAL] error case from the ERRORS section.

IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/43 is applied, updating the [EAGAIN] error in the ERRORS section from "the process would be delayed" to "the thread would be delayed".

Issue 7

SD5-XSH-ERN-220 is applied.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0192 [105], XSH/TC1-2008/0193 [79], XSH/TC1-2008/0194 [225], XSH/TC1-2008/0195 [450], XSH/TC1-2008/0196 [450], and XSH/TC1-2008/0197 [14] are applied.

End of informative text.


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