The Open Group Base Specifications Issue 7
IEEE Std 1003.1, 2013 Edition
Copyright © 2001-2013 The IEEE and The Open Group


fgetc - get a byte from a stream


#include <stdio.h>

int fgetc(FILE *


[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]

If the end-of-file indicator for the input stream pointed to by stream is not set and a next byte is present, the fgetc() function shall obtain the next byte as an unsigned char converted to an int, from the input stream pointed to by stream, and advance the associated file position indicator for the stream (if defined). Since fgetc() operates on bytes, reading a character consisting of multiple bytes (or "a multi-byte character") may require multiple calls to fgetc().

[CX] [Option Start] The fgetc() 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(). [Option End]


Upon successful completion, fgetc() shall return the next byte from the input stream pointed to by stream. If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-of-file indicator for the stream shall be set and fgetc() shall return EOF. If a read error occurs, the error indicator for the stream shall be set, fgetc() shall return EOF, [CX] [Option Start]  and shall set errno to indicate the error. [Option End]


The fgetc() function shall fail if data needs to be read and:

[CX] [Option Start] The O_NONBLOCK flag is set for the file descriptor underlying stream and the thread would be delayed in the fgetc() operation. [Option End]
[CX] [Option Start] The file descriptor underlying stream is not a valid file descriptor open for reading. [Option End]
[CX] [Option Start] The read 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 in a background process group attempting to read from its controlling terminal, and either the calling thread is blocking SIGTTIN or the process is ignoring SIGTTIN or the process group of the process is orphaned. This error may also be generated for implementation-defined reasons. [Option End]
[CX] [Option Start] The file is a regular file and an attempt was made to read at or beyond the offset maximum associated with the corresponding stream. [Option End]

The fgetc() function may fail if:

[CX] [Option Start] Insufficient storage space is available. [Option End]
[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.




If the integer value returned by fgetc() is stored into a variable of type char and then compared against the integer constant EOF, the comparison may never succeed, because sign-extension of a variable of type char on widening to integer is implementation-defined.

The ferror() or feof() functions must be used to distinguish between an error condition and an end-of-file condition.






Standard I/O Streams, feof, ferror, fgets, fread, fscanf, getchar, getc, gets, ungetc

XBD <stdio.h>


First released in Issue 1. Derived from Issue 1 of the SVID.

Issue 5

Large File Summit extensions are added.

Issue 6

Extensions beyond the ISO C standard are marked.

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

The following changes are made for alignment with the ISO/IEC 9899:1999 standard:

IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/32 is applied, updating the [EAGAIN] error in the ERRORS section from "the process would be delayed" to "the thread would be delayed".

Issue 7

Austin Group Interpretation 1003.1-2001 #051 is applied, updating the list of functions that mark the last data access timestamp for update.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0129 [79] and XSH/TC1-2008/0130 [14] are applied.

End of informative text.


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