Tribblix: manual page: fgetc.3c

FGETC(3C) Standard C Library Functions FGETC(3C)

NAME

fgetc, getc, getc_unlocked, getchar, getchar_unlocked, getw - get a
byte from a stream

SYNOPSIS

#include <stdio.h>

int fgetc(FILE *stream);

int getc(FILE *stream);

int getc_unlocked(FILE *stream);

int getchar(void);

int getchar_unlocked(void);

int getw(FILE *stream);

DESCRIPTION

The fgetc() function obtains the next byte (if present) as an
unsigned char converted to an int, from the input stream pointed to
by stream, and advances the associated file position indicator for
the stream (if defined).

For standard-conforming (see standards(7)) applications, if the end-
of-file indicator for the stream is set, fgetc() returns EOF whether
or not a next byte is present.

The fgetc() function may mark the st_atime field of the file
associated with stream for update. The st_atime field will be marked
for update by the first successful execution of fgetc(), fgets(3C),
fread(3C), fscanf(3C), getc(), getchar(), gets(3C) or scanf(3C) using
stream that returns data not supplied by a prior call to ungetc(3C)
or ungetwc(3C).

The getc() function is functionally identical to fgetc(), except that
it is implemented as a macro. It runs faster than fgetc(), but it
takes up more space per invocation and its name cannot be passed as
an argument to a function call.

The getchar() routine is equivalent to getc(stdin). It is implemented
as a macro.

The getc_unlocked() and getchar_unlocked() routines are variants of
getc() and getchar(), respectively, that do not lock the stream. It
is the caller's responsibility to acquire the stream lock before
calling these routines and releasing the lock afterwards; see
flockfile(3C) and stdio(3C). These routines are implemented as
macros.

The getw() function reads the next word from the stream. The size of
a word is the size of an int and may vary from environment to
environment. The getw() function presumes no special alignment in
the file.

The getw() function may mark the st_atime field of the file
associated with stream for update. The st_atime field will be marked
for update by the first successful execution of fgetc(), fgets(3C),
fread(3C), getc(), getchar(), gets(3C), fscanf(3C) or scanf(3C) using
stream that returns data not supplied by a prior call to ungetc(3C).

RETURN VALUES

Upon successful completion, fgetc(), getc(), getc_unlocked(),
getchar(), getchar_unlocked(), and getw() return the next byte from
the input stream pointed to by stream. If the stream is at end-of-
file, the end-of-file indicator for the stream is set and these
functions return EOF. For standard-conforming (see standards(7))
applications, if the end-of-file indicator for the stream is set,
these functions return EOF whether or not the stream is at end-of-
file. If a read error occurs, the error indicator for the stream is
set, EOF is returned, and errno is set to indicate the error.

ERRORS

The fgetc(), getc(), getc_unlocked(), getchar(), getchar_unlocked(),
and getw() functions will fail if data needs to be read and:

EAGAIN
The O_NONBLOCK flag is set for the file descriptor
underlying stream and the process would be delayed in
the fgetc() operation.

EBADF
The file descriptor underlying stream is not a valid
file descriptor open for reading.

EINTR
The read operation was terminated due to the receipt of
a signal, and no data was transferred.

EIO
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 process is ignoring
or blocking the SIGTTIN signal or the process group is
orphaned. This error may also be generated for
implementation-dependent reasons.

EOVERFLOW
The file is a regular file and an attempt was made to
read at or beyond the offset maximum associated with the
corresponding stream.

The fgetc(), getc(), getc_unlocked(), getchar(), getchar_unlocked(),
and getw() functions may fail if:

ENOMEM
Insufficient storage space is available.

ENXIO
A request was made of a non-existent device, or the request
was outside the capabilities of the device.

USAGE

If the integer value returned by fgetc(), getc(), getc_unlocked(),
getchar(), getchar_unlocked(), and getw() 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-dependent.

The ferror(3C) or feof(3C) functions must be used to distinguish
between an error condition and an end-of-file condition.

Functions exist for the getc(), getc_unlocked(), getchar(), and
getchar_unlocked() macros. To get the function form, the macro name
must be undefined (for example, #undef getc).

When the macro forms are used, getc() and getc_unlocked() evaluate
the stream argument more than once. In particular, getc(*f++); does
not work sensibly. The fgetc() function should be used instead when
evaluating the stream argument has side effects.

Because of possible differences in word length and byte ordering,
files written using getw() are machine-dependent, and may not be read
using getw() on a different processor.

The getw() function is inherently byte stream-oriented and is not
tenable in the context of either multibyte character streams or wide-
character streams. Application programmers are recommended to use
one of the character-based input functions instead.

ATTRIBUTES

NOTES

The fgetc(), getc(), getchar(), and getw() routines are MT-Safe in
multithreaded applications. The getc_unlocked() and
getchar_unlocked() routines are unsafe in multithreaded applications.

October 15, 2003 FGETC(3C)