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46 .TH FGETC 3C "Oct 15, 2003"
47 .SH NAME
48 fgetc, getc, getc_unlocked, getchar, getchar_unlocked, getw \- get a byte from
49 a stream
50 .SH SYNOPSIS
51 .LP
52 .nf
53 #include <stdio.h>
55 \fBint\fR \fBfgetc\fR(\fBFILE *\fR\fIstream\fR);
56 .fi
58 .LP
59 .nf
60 \fBint\fR \fBgetc\fR(\fBFILE *\fR\fIstream\fR);
61 .fi
63 .LP
64 .nf
65 \fBint\fR \fBgetc_unlocked\fR(\fBFILE *\fR\fIstream\fR);
66 .fi
68 .LP
69 .nf
70 \fBint\fR \fBgetchar\fR(\fBvoid\fR);
71 .fi
73 .LP
74 .nf
75 \fBint\fR \fBgetchar_unlocked\fR(\fBvoid\fR);
76 .fi
78 .LP
79 .nf
80 \fBint\fR \fBgetw\fR(\fBFILE *\fR\fIstream\fR);
81 .fi
83 .SH DESCRIPTION
84 .sp
85 .LP
86 The \fBfgetc()\fR function obtains the next byte (if present) as an \fBunsigned
87 char\fR converted to an \fBint\fR, from the input stream pointed to by
88 \fIstream\fR, and advances the associated file position indicator for the
89 stream (if defined).
90 .sp
91 .LP
92 For standard-conforming (see \fBstandards\fR(5)) applications, if the
93 end-of-file indicator for the stream is set, \fBfgetc()\fR returns \fBEOF\fR
94 whether or not a next byte is present.
95 .sp
96 .LP
97 The \fBfgetc()\fR function may mark the \fBst_atime\fR field of the file
98 associated with \fIstream\fR for update. The \fBst_atime\fR field will be
99 marked for update by the first successful execution of \fBfgetc()\fR,
100 \fBfgets\fR(3C), \fBfread\fR(3C), \fBfscanf\fR(3C), \fBgetc()\fR,
101 \fBgetchar()\fR, \fBgets\fR(3C) or \fBscanf\fR(3C) using \fIstream\fR that
102 returns data not supplied by a prior call to \fBungetc\fR(3C) or
103 \fBungetwc\fR(3C).
104 .sp
105 .LP
106 The \fBgetc()\fR function is functionally identical to \fBfgetc()\fR, except
107 that it is implemented as a macro. It runs faster than \fBfgetc()\fR, but it
108 takes up more space per invocation and its name cannot be passed as an argument
109 to a function call.
110 .sp
111 .LP
112 The \fBgetchar()\fR routine is equivalent to \fBgetc(stdin)\fR. It is
113 implemented as a macro.
114 .sp
115 .LP
116 The \fBgetc_unlocked()\fR and \fBgetchar_unlocked()\fR routines are variants of
117 \fBgetc()\fR and \fBgetchar()\fR, respectively, that do not lock the stream.
118 It is the caller's responsibility to acquire the stream lock before calling
119 these routines and releasing the lock afterwards; see \fBflockfile\fR(3C) and
120 \fBstdio\fR(3C). These routines are implemented as macros.
121 .sp
122 .LP
123 The \fBgetw()\fR function reads the next word from the \fIstream\fR. The size
124 of a word is the size of an \fBint\fR and may vary from environment to
125 environment. The \fBgetw()\fR function presumes no special alignment in the
126 file.
127 .sp
128 .LP
129 The \fBgetw()\fR function may mark the \fBst_atime\fR field of the file
130 associated with \fIstream\fR for update. The \fBst_atime\fR field will be
131 marked for update by the first successful execution of \fBfgetc()\fR,
132 \fBfgets\fR(3C), \fBfread\fR(3C), \fBgetc()\fR, \fBgetchar()\fR,
133 \fBgets\fR(3C), \fBfscanf\fR(3C) or \fBscanf\fR(3C) using \fIstream\fR that
134 returns data not supplied by a prior call to \fBungetc\fR(3C).
135 .SH RETURN VALUES
136 .sp
137 .LP
138 Upon successful completion, \fBfgetc()\fR, \fBgetc()\fR, \fBgetc_unlocked()\fR,
139 \fBgetchar()\fR, \fBgetchar_unlocked()\fR, and \fBgetw()\fR return the next
140 byte from the input stream pointed to by \fIstream\fR. If the stream is at
141 end-of-file, the end-of-file indicator for the stream is set and these
142 functions return \fBEOF\fR. For standard-conforming (see \fBstandards\fR(5))
143 applications, if the end-of-file indicator for the stream is set, these
144 functions return \fBEOF\fR whether or not the stream is at end-of-file. If a
145 read error occurs, the error indicator for the stream is set, \fBEOF\fR is
146 returned, and \fBerrno\fR is set to indicate the error.
147 .SH ERRORS
148 .sp
149 .LP
150 The \fBfgetc()\fR, \fBgetc()\fR, \fBgetc_unlocked()\fR, \fBgetchar()\fR,
151 \fBgetchar_unlocked()\fR, and \fBgetw()\fR functions will fail if data needs to
152 be read and:
153 .sp
154 .ne 2
155 .na
156 \fB\fBEAGAIN\fR\fR
157 .ad
158 .RS 13n
159 The \fBO_NONBLOCK\fR flag is set for the file descriptor underlying
160 \fIstream\fR and the process would be delayed in the \fBfgetc()\fR operation.
161 .RE
163 .sp
164 .ne 2
165 .na
166 \fB\fBEBADF\fR\fR
167 .ad
168 .RS 13n
169 The file descriptor underlying \fIstream\fR is not a valid file descriptor open
170 for reading.
171 .RE
173 .sp
174 .ne 2
175 .na
176 \fB\fBEINTR\fR\fR
177 .ad
178 .RS 13n
179 The read operation was terminated due to the receipt of a signal, and no data
180 was transferred.
181 .RE
183 .sp
184 .ne 2
185 .na
186 \fB\fBEIO\fR\fR
187 .ad
188 .RS 13n
189 A physical I/O error has occurred, or the process is in a background process
190 group attempting to read from its controlling terminal, and either the process
191 is ignoring or blocking the \fBSIGTTIN\fR signal or the process group is
192 orphaned. This error may also be generated for implementation-dependent
193 reasons.
194 .RE
196 .sp
197 .ne 2
198 .na
199 \fB\fBEOVERFLOW\fR\fR
200 .ad
201 .RS 13n
202 The file is a regular file and an attempt was made to read at or beyond the
203 offset maximum associated with the corresponding stream.
204 .RE
206 .sp
207 .LP
208 The \fBfgetc()\fR, \fBgetc()\fR, \fBgetc_unlocked()\fR, \fBgetchar()\fR,
209 \fBgetchar_unlocked()\fR, and \fBgetw()\fR functions may fail if:
210 .sp
211 .ne 2
212 .na
213 \fB\fBENOMEM\fR\fR
214 .ad
215 .RS 10n
216 Insufficient storage space is available.
217 .RE
219 .sp
220 .ne 2
221 .na
222 \fB\fBENXIO\fR\fR
223 .ad
224 .RS 10n
225 A request was made of a non-existent device, or the request was outside the
226 capabilities of the device.
227 .RE
229 .SH USAGE
230 .sp
231 .LP
232 If the integer value returned by \fBfgetc()\fR, \fBgetc()\fR,
233 \fBgetc_unlocked()\fR, \fBgetchar()\fR, \fBgetchar_unlocked()\fR, and
234 \fBgetw()\fR is stored into a variable of type \fBchar\fR and then compared
235 against the integer constant EOF, the comparison may never succeed, because
236 sign-extension of a variable of type \fBchar\fR on widening to integer is
237 implementation-dependent.
238 .sp
239 .LP
240 The \fBferror\fR(3C) or \fBfeof\fR(3C) functions must be used to distinguish
241 between an error condition and an end-of-file condition.
242 .sp
243 .LP
244 Functions exist for the \fBgetc()\fR, \fBgetc_unlocked()\fR, \fBgetchar()\fR,
245 and \fBgetchar_unlocked()\fR macros. To get the function form, the macro name
246 must be undefined (for example, \fB#undef getc\fR).
247 .sp
248 .LP
249 When the macro forms are used, \fBgetc()\fR and \fBgetc_unlocked()\fR evaluate
250 the \fIstream\fR argument more than once. In particular,
251 \fBgetc(*\fR\fIf++\fR\fB);\fR does not work sensibly. The \fBfgetc()\fR
252 function should be used instead when evaluating the \fIstream\fR argument has
253 side effects.
254 .sp
255 .LP
256 Because of possible differences in word length and byte ordering, files written
257 using \fBgetw()\fR are machine-dependent, and may not be read using
258 \fBgetw()\fR on a different processor.
259 .sp
260 .LP
261 The \fBgetw()\fR function is inherently byte stream-oriented and is not tenable
262 in the context of either multibyte character streams or wide-character streams.
263 Application programmers are recommended to use one of the character-based input
264 functions instead.
265 .SH ATTRIBUTES
266 .sp
267 .LP
268 See \fBattributes\fR(5) for descriptions of the following attributes:
269 .sp
271 .sp
272 .TS
273 box;
274 c | c
275 l | l .
276 ATTRIBUTE TYPE ATTRIBUTE VALUE
277 _
278 Interface Stability T{
279 \fBfgetc()\fR, \fBgetc()\fR, \fBgetc_unlocked()\fR, \fBgetchar()\fR, and \fBgetchar_unlocked()\fR are Standard.
280 T}
281 _
282 MT-Level See \fBNOTES\fR below.
283 .TE
285 .SH SEE ALSO
286 .sp
287 .LP
288 \fBIntro\fR(3), \fB__fsetlocking\fR(3C), \fBfclose\fR(3C), \fBfeof\fR(3C),
289 \fBfgets\fR(3C), \fBfgetwc\fR(3C), \fBfgetws\fR(3C), \fBflockfile\fR(3C),
290 \fBfopen\fR(3C), \fBfread\fR(3C), \fBfscanf\fR(3C), \fBgets\fR(3C),
291 \fBputc\fR(3C), \fBscanf\fR(3C), \fBstdio\fR(3C), \fBungetc\fR(3C),
292 \fBungetwc\fR(3C), \fBattributes\fR(5), \fBstandards\fR(5)
293 .SH NOTES
294 .sp
295 .LP
296 The \fBfgetc()\fR, \fBgetc()\fR, \fBgetchar()\fR, and \fBgetw()\fR routines are
297 MT-Safe in multithreaded applications. The \fBgetc_unlocked()\fR and
298 \fBgetchar_unlocked()\fR routines are unsafe in multithreaded applications.