230 lines
9.7 KiB
HTML
230 lines
9.7 KiB
HTML
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<title>strtok</title>
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<basefont size="3"> <a name="strtok"></a> <a name="tag_03_742"></a><!-- strtok -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_742_01"></a>NAME</h4>
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<blockquote>strtok, strtok_r - split string into tokens</blockquote>
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<h4><a name="tag_03_742_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/string.h.html">string.h</a>><br>
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<br>
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char *strtok(char *restrict</tt> <i>s1</i><tt>, const char *restrict</tt> <i>s2</i><tt>);<br>
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</tt></code></p>
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('TSF')">TSF</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> char *strtok_r(char *restrict</tt> <i>s</i><tt>, const char *restrict</tt> <i>sep</i><tt>,<br>
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char **restrict</tt> <i>lasts</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]"
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border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_742_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>For <i>strtok</i>(): <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any
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conflict between the requirements described here and the ISO C standard is unintentional. This volume of
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IEEE Std 1003.1-2001 defers to the ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border=
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"0"></p>
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<p>A sequence of calls to <i>strtok</i>() breaks the string pointed to by <i>s1</i> into a sequence of tokens, each of which is
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delimited by a byte from the string pointed to by <i>s2</i>. The first call in the sequence has <i>s1</i> as its first argument,
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and is followed by calls with a null pointer as their first argument. The separator string pointed to by <i>s2</i> may be different
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from call to call.</p>
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<p>The first call in the sequence searches the string pointed to by <i>s1</i> for the first byte that is <i>not</i> contained in
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the current separator string pointed to by <i>s2</i>. If no such byte is found, then there are no tokens in the string pointed to
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by <i>s1</i> and <i>strtok</i>() shall return a null pointer. If such a byte is found, it is the start of the first token.</p>
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<p>The <i>strtok</i>() function then searches from there for a byte that <i>is</i> contained in the current separator string. If no
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such byte is found, the current token extends to the end of the string pointed to by <i>s1</i>, and subsequent searches for a token
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shall return a null pointer. If such a byte is found, it is overwritten by a null byte, which terminates the current token. The
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<i>strtok</i>() function saves a pointer to the following byte, from which the next search for a token shall start.</p>
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<p>Each subsequent call, with a null pointer as the value of the first argument, starts searching from the saved pointer and
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behaves as described above.</p>
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<p>The implementation shall behave as if no function defined in this volume of IEEE Std 1003.1-2001 calls
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<i>strtok</i>().</p>
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<p><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The
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<i>strtok</i>() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe.
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<img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p><sup>[<a href="javascript:open_code('TSF')">TSF</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The <i>strtok_r</i>() function considers the null-terminated string <i>s</i> as a sequence of zero or more text tokens separated by
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spans of one or more characters from the separator string <i>sep</i>. The argument <i>lasts</i> points to a user-provided pointer
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which points to stored information necessary for <i>strtok_r</i>() to continue scanning the same string.</p>
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<p>In the first call to <i>strtok_r</i>(), <i>s</i> points to a null-terminated string, <i>sep</i> to a null-terminated string of
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separator characters, and the value pointed to by <i>lasts</i> is ignored. The <i>strtok_r</i>() function shall return a pointer to
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the first character of the first token, write a null character into <i>s</i> immediately following the returned token, and update
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the pointer to which <i>lasts</i> points.</p>
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<p>In subsequent calls, <i>s</i> is a NULL pointer and <i>lasts</i> shall be unchanged from the previous call so that subsequent
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calls shall move through the string <i>s</i>, returning successive tokens until no tokens remain. The separator string <i>sep</i>
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may be different from call to call. When no token remains in <i>s</i>, a NULL pointer shall be returned. <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_742_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>strtok</i>() shall return a pointer to the first byte of a token. Otherwise, if there is no
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token, <i>strtok</i>() shall return a null pointer.</p>
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<p><sup>[<a href="javascript:open_code('TSF')">TSF</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The <i>strtok_r</i>() function shall return a pointer to the token found, or a NULL pointer when no token is found. <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_742_05"></a>ERRORS</h4>
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<blockquote>
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<p>No errors are defined.</p>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_742_06"></a>EXAMPLES</h4>
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<blockquote>
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<h5><a name="tag_03_742_06_01"></a>Searching for Word Separators</h5>
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<p>The following example searches for tokens separated by <space>s.</p>
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<pre>
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<tt>#include <string.h>
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...
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char *token;
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char *line = "LINE TO BE SEPARATED";
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char *search = " ";
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<br>
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/* Token will point to "LINE". */
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token = strtok(line, search);
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<br>
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/* Token will point to "TO". */
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token = strtok(NULL, search);
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</tt>
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</pre>
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<h5><a name="tag_03_742_06_02"></a>Breaking a Line</h5>
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<p>The following example uses <i>strtok</i>() to break a line into two character strings separated by any combination of
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<space>s, <tab>s, or <newline>s.</p>
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<pre>
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<tt>#include <string.h>
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...
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struct element {
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char *key;
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char *data;
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};
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...
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char line[LINE_MAX];
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char *key, *data;
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...
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key = strtok(line, " \n");
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data = strtok(NULL, " \n");
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...
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_742_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The <i>strtok_r</i>() function is thread-safe and stores its state in a user-supplied buffer instead of possibly using a static
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data area that may be overwritten by an unrelated call from another thread.</p>
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</blockquote>
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<h4><a name="tag_03_742_08"></a>RATIONALE</h4>
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<blockquote>
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<p>The <i>strtok</i>() function searches for a separator string within a larger string. It returns a pointer to the last substring
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between separator strings. This function uses static storage to keep track of the current string position between calls. The new
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function, <i>strtok_r</i>(), takes an additional argument, <i>lasts</i>, to keep track of the current position in the string.</p>
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</blockquote>
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<h4><a name="tag_03_742_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_742_10"></a>SEE ALSO</h4>
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<blockquote>
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<p>The Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/string.h.html"><i><string.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_742_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 1. Derived from Issue 1 of the SVID.</p>
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</blockquote>
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<h4><a name="tag_03_742_12"></a>Issue 5</h4>
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<blockquote>
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<p>The <i>strtok_r</i>() function is included for alignment with the POSIX Threads Extension.</p>
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<p>A note indicating that the <i>strtok</i>() function need not be reentrant is added to the DESCRIPTION.</p>
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</blockquote>
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<h4><a name="tag_03_742_13"></a>Issue 6</h4>
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<blockquote>
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<p>Extensions beyond the ISO C standard are marked.</p>
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<p>The <i>strtok_r</i>() function is marked as part of the Thread-Safe Functions option.</p>
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<p>In the DESCRIPTION, the note about reentrancy is expanded to cover thread-safety.</p>
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<p>The APPLICATION USAGE section is updated to include a note on the thread-safe function and its avoidance of possibly using a
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static data area.</p>
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<p>The <b>restrict</b> keyword is added to the <i>strtok</i>() and <i>strtok_r</i>() prototypes for alignment with the
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ISO/IEC 9899:1999 standard.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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