man3/gets.3

   1 .\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
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  23 .\" Modified Wed Jul 28 11:12:07 1993 by Rik Faith (faith@cs.unc.edu)
  24 .\" Modified Fri Sep  8 15:48:13 1995 by Andries Brouwer (aeb@cwi.nl)
  25 .TH GETS 3  1993-04-04 "GNU" "Linux Programmer's Manual"
  26 .SH NAME
  27 fgetc, fgets, getc, getchar, gets, ungetc \- input of characters and strings
  28 .SH SYNOPSIS
  29 .nf
  30 .B #include <stdio.h>
  31 .sp
  32 .BI "int fgetc(FILE *" stream );
  33 .nl
  34 .BI "char *fgets(char *" "s" ", int " "size" ", FILE *" "stream" );
  35 .nl
  36 .BI "int getc(FILE *" stream );
  37 .nl
  38 .BI "int getchar(void);"
  39 .nl
  40 .BI "char *gets(char *" "s" );
  41 .nl
  42 .BI "int ungetc(int " c ", FILE *" stream );
  43 .SH DESCRIPTION
  44 .BR fgetc ()
  45 reads the next character from
  46 .I stream
  47 and returns it as an
  48 .I unsigned char
  49 cast to an
  50 .IR int ,
  51 or
  52 .B EOF
  53 on end of file or error.
  54 .PP
  55 .BR getc ()
  56 is equivalent to
  57 .BR fgetc ()
  58 except that it may be implemented as a macro which evaluates
  59 .I stream
  60 more than once.
  61 .PP
  62 .BR getchar ()
  63 is equivalent to
  64 .BI "getc(" stdin ) \fR.
  65 .PP
  66 .BR gets ()
  67 reads a line from
  68 .I stdin
  69 into the buffer pointed to by
  70 .I s
  71 until either a terminating newline or
  72 .BR EOF ,
  73 which it replaces with
  74 .BR '\e0' .
  75 No check for buffer overrun is performed (see
  76 .B BUGS
  77 below).
  78 .PP
  79 .BR fgets ()
  80 reads in at most one less than
  81 .I size
  82 characters from
  83 .I stream
  84 and stores them into the buffer pointed to by
  85 .IR s .
  86 Reading stops after an
  87 .B EOF
  88 or a newline.  If a newline is read, it is stored into the buffer.  A
  89 .B '\e0'
  90 is stored after the last character in the buffer.
  91 .PP
  92 .BR ungetc ()
  93 pushes
  94 .I c
  95 back to
  96 .IR stream ,
  97 cast to
  98 .IR "unsigned char" ,
  99 where it is available for subsequent read operations.  Pushed-back characters
 100 will be returned in reverse order; only one pushback is guaranteed.
 101 .PP
 102 Calls to the functions described here can be mixed with each other and with
 103 calls to other input functions from the
 104 .B stdio
 105 library for the same input stream.
 106 .PP
 107 For non-locking counterparts, see
 108 .BR unlocked_stdio (3).
 109 .SH "RETURN VALUE"
 110 .BR fgetc (),
 111 .BR getc ()
 112 and
 113 .BR getchar ()
 114 return the character read as an
 115 .I unsigned char
 116 cast to an
 117 .I int
 118 or
 119 .B EOF
 120 on end of file or error.
 121 .PP
 122 .BR gets ()
 123 and
 124 .BR fgets ()
 125 return
 126 .I s
 127 on success, and NULL
 128 on error or when end of file occurs while no characters have been read.
 129 .PP
 130 .BR ungetc ()
 131 returns
 132 .I c
 133 on success, or
 134 .B EOF
 135 on error.
 136 .SH "CONFORMING TO"
 137 ANSI-C, POSIX.1.
 138 LSB deprecates
 139 .BR gets ().
 140 .SH BUGS
 141 Never use
 142 .BR gets ().
 143 Because it is impossible to tell without knowing the data in advance how many
 144 characters
 145 .BR gets ()
 146 will read, and because
 147 .BR gets ()
 148 will continue to store characters past the end of the buffer, it is extremely
 149 dangerous to use.  It has been used to break computer security.  Use
 150 .BR fgets ()
 151 instead.
 152 .PP
 153 It is not advisable to mix calls to input functions from the
 154 .B stdio
 155 library with low-level calls to
 156 .BR read ()
 157 for the file descriptor associated with the input stream; the results
 158 will be undefined and very probably not what you want.
 159 .SH "SEE ALSO"
 160 .BR read (2),
 161 .BR write (2),
 162 .BR ferror (3),
 163 .BR fgetwc (3),
 164 .BR fgets (3),
 165 .BR fopen (3),
 166 .BR fread (3),
 167 .BR fseek (3),
 168 .BR getwchar (3),
 169 .BR puts (3),
 170 .BR scanf (3),
 171 .BR ungetwc (3),
 172 .BR unlocked_stdio (3)