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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(), getdelim(3C), getline(3C), 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 argu‐
ment 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 afterward; 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 environ‐
ment. 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 under‐
lying 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 con‐
trolling 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 implementa‐
tion-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 corre‐
sponding 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 com‐
parison 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 evalu‐
ating 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 ten‐
able in the context of either multibyte character streams or wide-char‐
acter streams. Application programmers are recommended to use one of
the character-based input functions instead.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityT{ fgetc(), getc(), getc_unlocked(),
getchar(), and getchar_unlocked() are Standard. T} _ MT-LevelSee NOTES
below.
SEE ALSO
__fsetlocking(3C), fclose(3C), feof(3C), fgets(3C), fgetwc(3C),
fgetws(3C), flockfile(3C), fopen(3C), fread(3C), fscanf(3C), getde‐
lim(3C), getline(3C), gets(3C), putc(3C), scanf(3C), stdio(3C),
ungetc(3C), ungetwc(3C), intro(3), attributes(7), standards(7)
NOTES
The fgetc(), getc(), getchar(), and getw() routines are MT-Safe in mul‐
tithreaded applications. The getc_unlocked() and getchar_unlocked()
routines are unsafe in multithreaded applications.
Oracle Solaris 11.4 11 May 2021 fgetc(3C)