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  53. <a name="fwide_002d_002d_002dset-and-determine-the-orientation-of-a-FILE-stream"></a>
  54. <h3 class="section">4.31 <code>fwide</code>&mdash;set and determine the orientation of a FILE stream</h3>
  55. <a name="index-fwide"></a>
  56. <a name="index-_005ffwide_005fr"></a>
  57. <p><strong>Synopsis</strong>
  58. </p><div class="example">
  59. <pre class="example">#include &lt;wchar.h&gt;
  60. int fwide(FILE *<var>fp</var>, int <var>mode</var>);
  61. int _fwide_r(struct _reent *<var>ptr</var>, FILE *<var>fp</var>, int <var>mode</var>);
  62. </pre></div>
  63. <p><strong>Description</strong><br>
  64. When <var>mode</var> is zero, the <code>fwide</code> function determines the current
  65. orientation of <var>fp</var>. It returns a value &gt; 0 if <var>fp</var> is
  66. wide-character oriented, i.e. if wide character I/O is permitted but
  67. char I/O is disallowed. It returns a value &lt; 0 if <var>fp</var> is byte
  68. oriented, i.e. if char I/O is permitted but wide character I/O is
  69. disallowed. It returns zero if <var>fp</var> has no orientation yet; in
  70. this case the next I/O operation might change the orientation (to byte
  71. oriented if it is a char I/O operation, or to wide-character oriented
  72. if it is a wide character I/O operation).
  73. </p>
  74. <p>Once a stream has an orientation, it cannot be changed and persists
  75. until the stream is closed, unless the stream is re-opened with freopen,
  76. which removes the orientation of the stream.
  77. </p>
  78. <p>When <var>mode</var> is non-zero, the <code>fwide</code> function first attempts to set
  79. <var>fp</var>&rsquo;s orientation (to wide-character oriented if <var>mode</var> &gt; 0, or to
  80. byte oriented if <var>mode</var> &lt; 0). It then returns a value denoting the
  81. current orientation, as above.
  82. </p>
  83. <br>
  84. <p><strong>Returns</strong><br>
  85. The <code>fwide</code> function returns <var>fp</var>&rsquo;s orientation, after possibly
  86. changing it. A return value &gt; 0 means wide-character oriented. A return
  87. value &lt; 0 means byte oriented. A return value of zero means undecided.
  88. </p>
  89. <br>
  90. <p><strong>Portability</strong><br>
  91. C99, POSIX.1-2001.
  92. </p>
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