1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
<head>
<title>GNU Octave: Opening and Closing Files</title>
<meta name="description" content="GNU Octave: Opening and Closing Files">
<meta name="keywords" content="GNU Octave: Opening and Closing Files">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link href="index.html#Top" rel="start" title="Top">
<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="C_002dStyle-I_002fO-Functions.html#C_002dStyle-I_002fO-Functions" rel="up" title="C-Style I/O Functions">
<link href="Simple-Output.html#Simple-Output" rel="next" title="Simple Output">
<link href="C_002dStyle-I_002fO-Functions.html#C_002dStyle-I_002fO-Functions" rel="prev" title="C-Style I/O Functions">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.indentedblock {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
div.smalllisp {margin-left: 3.2em}
kbd {font-style:oblique}
pre.display {font-family: inherit}
pre.format {font-family: inherit}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: inherit; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: inherit; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.nocodebreak {white-space:nowrap}
span.nolinebreak {white-space:nowrap}
span.roman {font-family:serif; font-weight:normal}
span.sansserif {font-family:sans-serif; font-weight:normal}
ul.no-bullet {list-style: none}
-->
</style>
</head>
<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
<a name="Opening-and-Closing-Files"></a>
<div class="header">
<p>
Next: <a href="Simple-Output.html#Simple-Output" accesskey="n" rel="next">Simple Output</a>, Up: <a href="C_002dStyle-I_002fO-Functions.html#C_002dStyle-I_002fO-Functions" accesskey="u" rel="up">C-Style I/O Functions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Opening-and-Closing-Files-1"></a>
<h4 class="subsection">14.2.1 Opening and Closing Files</h4>
<p>When reading data from a file it must be opened for reading first, and
likewise when writing to a file. The <code>fopen</code> function returns a
pointer to an open file that is ready to be read or written. Once all
data has been read from or written to the opened file it should be closed.
The <code>fclose</code> function does this. The following code illustrates
the basic pattern for writing to a file, but a very similar pattern is
used when reading a file.
</p>
<div class="example">
<pre class="example">filename = "myfile.txt";
fid = fopen (filename, "w");
# Do the actual I/O here…
fclose (fid);
</pre></div>
<a name="XREFfopen"></a><dl>
<dt><a name="index-fopen"></a>Built-in Function: <em>[<var>fid</var>, <var>msg</var>] =</em> <strong>fopen</strong> <em>(<var>name</var>, <var>mode</var>, <var>arch</var>)</em></dt>
<dt><a name="index-fopen-1"></a>Built-in Function: <em><var>fid_list</var> =</em> <strong>fopen</strong> <em>("all")</em></dt>
<dt><a name="index-fopen-2"></a>Built-in Function: <em>[<var>file</var>, <var>mode</var>, <var>arch</var>] =</em> <strong>fopen</strong> <em>(<var>fid</var>)</em></dt>
<dd><p>The first form of the <code>fopen</code> function opens the named file with
the specified mode (read-write, read-only, etc.) and architecture
interpretation (IEEE big endian, IEEE little endian, etc.), and returns
an integer value that may be used to refer to the file later. If an
error occurs, <var>fid</var> is set to -1 and <var>msg</var> contains the
corresponding system error message. The <var>mode</var> is a one or two
character string that specifies whether the file is to be opened for
reading, writing, or both.
</p>
<p>The second form of the <code>fopen</code> function returns a vector of file ids
corresponding to all the currently open files, excluding the
<code>stdin</code>, <code>stdout</code>, and <code>stderr</code> streams.
</p>
<p>The third form of the <code>fopen</code> function returns information about the
open file given its file id.
</p>
<p>For example,
</p>
<div class="example">
<pre class="example">myfile = fopen ("splat.dat", "r", "ieee-le");
</pre></div>
<p>opens the file <samp>splat.dat</samp> for reading. If necessary, binary
numeric values will be read assuming they are stored in IEEE format with
the least significant bit first, and then converted to the native
representation.
</p>
<p>Opening a file that is already open simply opens it again and returns a
separate file id. It is not an error to open a file several times,
though writing to the same file through several different file ids may
produce unexpected results.
</p>
<p>The possible values ‘<samp>mode</samp>’ may have are
</p>
<dl compact="compact">
<dt>‘<samp>r</samp>’</dt>
<dd><p>Open a file for reading.
</p>
</dd>
<dt>‘<samp>w</samp>’</dt>
<dd><p>Open a file for writing. The previous contents are discarded.
</p>
</dd>
<dt>‘<samp>a</samp>’</dt>
<dd><p>Open or create a file for writing at the end of the file.
</p>
</dd>
<dt>‘<samp>r+</samp>’</dt>
<dd><p>Open an existing file for reading and writing.
</p>
</dd>
<dt>‘<samp>w+</samp>’</dt>
<dd><p>Open a file for reading or writing. The previous contents are
discarded.
</p>
</dd>
<dt>‘<samp>a+</samp>’</dt>
<dd><p>Open or create a file for reading or writing at the end of the
file.
</p></dd>
</dl>
<p>Append a <code>"t"</code> to the mode string to open the file in text mode or a
<code>"b"</code> to open in binary mode. On Windows and Macintosh systems, text
mode reading and writing automatically converts linefeeds to the
appropriate line end character for the system (carriage-return linefeed
on Windows, carriage-return on Macintosh). The default if no mode is
specified is binary mode.
</p>
<p>Additionally, you may append a <code>"z"</code> to the mode string to open a
gzipped file for reading or writing. For this to be successful, you
must also open the file in binary mode.
</p>
<p>The parameter <var>arch</var> is a string specifying the default data format
for the file. Valid values for <var>arch</var> are:
</p>
<dl compact="compact">
<dt>‘<samp>native</samp>’</dt>
<dd><p>The format of the current machine (this is the default).
</p>
</dd>
<dt>‘<samp>ieee-be</samp>’</dt>
<dd><p>IEEE big endian format.
</p>
</dd>
<dt>‘<samp>ieee-le</samp>’</dt>
<dd><p>IEEE little endian format.
</p></dd>
</dl>
<p>however, conversions are currently only supported for ‘<samp>native</samp>’
‘<samp>ieee-be</samp>’, and ‘<samp>ieee-le</samp>’ formats.
</p>
<p><strong>See also:</strong> <a href="#XREFfclose">fclose</a>, <a href="Line_002dOriented-Input.html#XREFfgets">fgets</a>, <a href="Line_002dOriented-Input.html#XREFfgetl">fgetl</a>, <a href="Formatted-Input.html#XREFfscanf">fscanf</a>, <a href="Binary-I_002fO.html#XREFfread">fread</a>, <a href="Simple-Output.html#XREFfputs">fputs</a>, <a href="Simple-File-I_002fO.html#XREFfdisp">fdisp</a>, <a href="Formatted-Output.html#XREFfprintf">fprintf</a>, <a href="Binary-I_002fO.html#XREFfwrite">fwrite</a>, <a href="Line_002dOriented-Input.html#XREFfskipl">fskipl</a>, <a href="File-Positioning.html#XREFfseek">fseek</a>, <a href="File-Positioning.html#XREFfrewind">frewind</a>, <a href="File-Positioning.html#XREFftell">ftell</a>, <a href="EOF-and-Errors.html#XREFfeof">feof</a>, <a href="EOF-and-Errors.html#XREFferror">ferror</a>, <a href="EOF-and-Errors.html#XREFfclear">fclear</a>, <a href="Paging-Screen-Output.html#XREFfflush">fflush</a>, <a href="EOF-and-Errors.html#XREFfreport">freport</a>.
</p></dd></dl>
<a name="XREFfclose"></a><dl>
<dt><a name="index-fclose"></a>Built-in Function: <em></em> <strong>fclose</strong> <em>(<var>fid</var>)</em></dt>
<dt><a name="index-fclose-1"></a>Built-in Function: <em></em> <strong>fclose</strong> <em>("all")</em></dt>
<dd><p>Close the specified file. If successful, <code>fclose</code> returns 0,
otherwise, it returns -1. The second form of the <code>fclose</code> call closes
all open files except <code>stdout</code>, <code>stderr</code>, and <code>stdin</code>.
</p>
<p><strong>See also:</strong> <a href="#XREFfopen">fopen</a>, <a href="EOF-and-Errors.html#XREFfreport">freport</a>.
</p></dd></dl>
<a name="XREFis_005fvalid_005ffile_005fid"></a><dl>
<dt><a name="index-is_005fvalid_005ffile_005fid"></a>Function File: <em></em> <strong>is_valid_file_id</strong> <em>(<var>fid</var>)</em></dt>
<dd><p>Return true if <var>fid</var> refers to an open file.
</p>
<p><strong>See also:</strong> <a href="#XREFfopen">fopen</a>.
</p></dd></dl>
<hr>
<div class="header">
<p>
Next: <a href="Simple-Output.html#Simple-Output" accesskey="n" rel="next">Simple Output</a>, Up: <a href="C_002dStyle-I_002fO-Functions.html#C_002dStyle-I_002fO-Functions" accesskey="u" rel="up">C-Style I/O Functions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>
</body>
</html>
|
