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从www.CppReference.com打包的C++参考手册

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  <div class="name-format">
    strncat
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;string.h&gt;
  char *strncat( char *str1, const char *str2, size_t count );
</pre>

  <p>The function strncat() concatenates at most <em>count</em>
  characters of <em>str2</em> onto <em>str1</em>, adding a null
  termination. The resulting string is returned.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="strcat.html">strcat</a><br>
    <a href="strchr.html">strchr</a><br>
    <a href="strncmp.html">strncmp</a><br>
    <a href="strncpy.html">strncpy</a>
  </div>

  <p>Another set of related (but non-standard) functions are <a
  href="http://en.wikipedia.org/wiki/Strlcpy">strlcpy and
  strlcat</a>.</p>

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  <div class="name-format">
    strncmp
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;string.h&gt;
  int strncmp( const char *str1, const char *str2, size_t count );
</pre>

  <p>The strncmp() function compares at most <em>count</em> characters
  of <em>str1</em> and <em>str2</em>. The return value is as
  follows:</p>

  <table class="code-table">
    <tr>
      <th class="code-table-th">Return value</th>

      <th class="code-table-th">Explanation</th>
    </tr>

    <tr>
      <td class="code-table-td">less than 0</td>

      <td class="code-table-td">&#39;&#39;str1&#39;&#39; is less than
      &#39;&#39;str2&#39;&#39;</td>
    </tr>

    <tr>
      <td class="code-table-td">equal to 0</td>

      <td class="code-table-td">&#39;&#39;str1&#39;&#39; is equal to
      &#39;&#39;str2&#39;&#39;</td>
    </tr>

    <tr>
      <td class="code-table-td">greater than 0</td>

      <td class="code-table-td">&#39;&#39;str1&#39;&#39; is greater
      than str2&#39;&#39;</td>
    </tr>
  </table>

  <p>If there are less than <em>count</em> characters in either string,
  then the comparison will stop after the first null termination is
  encountered.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="strchr.html">strchr</a><br>
    <a href="strcmp.html">strcmp</a><br>
    <a href="strcpy.html">strcpy</a><br>
    <a href="strlen.html">strlen</a><br>
    <a href="strncat.html">strncat</a><br>
    <a href="strncpy.html">strncpy</a>
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<hr>

  <div class="name-format">
    strncpy
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;string.h&gt;
  char *strncpy( char *to, const char *from, size_t count );
</pre>

  <p>The strncpy() function copies at most <em>count</em> characters of
  <em>from</em> to the string <em>to</em>. If from has less than
  <em>count</em> characters, the remainder is padded with &#39;\0&#39;
  characters. The return value is the resulting string.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="memcpy.html">memcpy</a><br>
    <a href="strchr.html">strchr</a><br>
    <a href="strcpy.html">strcpy</a><br>
    <a href="strncat.html">strncat</a><br>
    <a href="strncmp.html">strncmp</a>
  </div>

  <p>Another set of related (but non-standard) functions are <a
  href="http://en.wikipedia.org/wiki/Strlcpy">strlcpy and
  strlcat</a>.</p>

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<hr>

  <div class="name-format">
    strpbrk
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;string.h&gt;
  char* strpbrk( const char* str1, const char* str2 );
</pre>

  <p>The function strpbrk() returns a pointer to the first ocurrence in
  <em>str1</em> of any character in <em>str2</em>, or
  <strong>NULL</strong> if no such characters are present.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    (C++ Algorithms) <a href=
    "../cppalgorithm/find_first_of.html">find_first_of</a><br>
    <a href="strchr.html">strchr</a><br>
    <a href="strcspn.html">strcspn</a><br>
    <a href="strrchr.html">strrchr</a><br>
    <a href="strspn.html">strspn</a><br>
    <a href="strstr.html">strstr</a><br>
    <a href="strtok.html">strtok</a>
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  <div class="name-format">
    strrchr
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;string.h&gt;
  char *strrchr( const char *str, int ch );
</pre>

  <p>The function strrchr() returns a pointer to the last occurrence of
  <em>ch</em> in <em>str</em>, or <strong>NULL</strong> if no match is
  found.</p>

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    Related topics:
  </div>

  <div class="related-content">
    <a href="strcspn.html">strcspn</a><br>
    <a href="strpbrk.html">strpbrk</a><br>
    <a href="strspn.html">strspn</a><br>
    <a href="strstr.html">strstr</a><br>
    <a href="strtok.html">strtok</a>
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<hr>

  <div class="name-format">
    strspn
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;string.h&gt;
  size_t strspn( const char *str1, const char *str2 );
</pre>

  <p>The strspn() function returns the index of the first character in
  <em>str1</em> that doesn&#39;t match any character in
  <em>str2</em>.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="strchr.html">strchr</a><br>
    <a href="strpbrk.html">strpbrk</a><br>
    <a href="strrchr.html">strrchr</a><br>
    <a href="strstr.html">strstr</a><br>
    <a href="strtok.html">strtok</a>
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<hr>

  <div class="name-format">
    strstr
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;string.h&gt;
  char *strstr( const char *str1, const char *str2 );
</pre>

  <p>The function strstr() returns a pointer to the first occurrence
  of <em>str2</em> in <em>str1</em>, or <strong>NULL</strong> if no
  match is found.  If the length of <em>str2</em> is zero, then
  strstr() will simply return <em>str1</em>.
  </p>

  <p>For example, the following code checks for the existence of one
  string within another string:</p>

  <pre class="example-code">
  char* str1 = "this is a string of characters";
  char* str2 = "a string";
  char* result = strstr( str1, str2 );
  if( result == NULL ) printf( "Could not find '%s' in '%s'\n", str2, str1 );
  else printf( "Found a substring: '%s'\n", result );
</pre>

  <p>When run, the above code displays this output:</p>
  <pre class="example-code">
  Found a substring: 'a string of characters'
</pre>

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    Related topics:
  </div>

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    <a href="memchr.html">memchr</a><br>
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    <a href="strpbrk.html">strpbrk</a><br>
    <a href="strrchr.html">strrchr</a><br>
    <a href="strspn.html">strspn</a><br>
    <a href="strtok.html">strtok</a>
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  <div class="name-format">
    strtod
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;stdlib.h&gt;
  double strtod( const char *start, char **end );
</pre>

  <p>The function strtod() returns whatever it encounters first in
  <em>start</em> as a double. <em>end</em> is set to point at whatever
  is left in <em>start</em> after that double. If overflow occurs,
  strtod() returns either <strong>HUGE_VAL</strong> or
  -<strong>HUGE_VAL</strong>.</p>

  <div class="related-name-format">
    Related topics:
  </div>

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    <a href="atof.html">atof</a>
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<hr>

  <div class="name-format">
    strtok
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;string.h&gt;
  char *strtok( char *str1, const char *str2 );
</pre>

  <p>The strtok() function returns a pointer to the next
  &quot;token&quot; in <em>str1</em>, where <em>str2</em> contains the
  delimiters that determine the token. strtok() returns
  <strong>NULL</strong> if no token is found. In order to convert a
  string to tokens, the first call to strtok() should have
  <em>str1</em> point to the string to be tokenized. All calls after
  this should have <em>str1</em> be <strong>NULL</strong>.</p>

  <p>For example:</p>
  <pre class="example-code">
   char str[] = &quot;now # is the time for all # good men to come to the # aid of their country&quot;;
   char delims[] = &quot;#&quot;;
   char *result = <strong>NULL</strong>;
   result = strtok( str, delims );
   while( result != <strong>NULL</strong> ) {
       printf( &quot;result is \&quot;%s\&quot;\n&quot;, result );
       result = strtok( <strong>NULL</strong>, delims );
   }            
</pre>

  <p>The above code will display the following output:</p>
  <pre class="example-code">
   result is &quot;now &quot;
   result is &quot; is the time for all &quot;
   result is &quot; good men to come to the &quot;
   result is &quot; aid of their country&quot;          
</pre>

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    Related topics:
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    <a href="strchr.html">strchr</a><br>
    <a href="strcspn.html">strcspn</a><br>
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    <a href="strrchr.html">strrchr</a><br>
    <a href="strspn.html">strspn</a><br>
    <a href="strstr.html">strstr</a>
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  <div class="name-format">
    strtol
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;stdlib.h&gt;
  long strtol( const char *start, char **end, int base );
</pre>

  <p>The strtol() function returns whatever it encounters first in
  <em>start</em> as a long, doing the conversion to <em>base</em> if
  necessary. <em>end</em> is set to point to whatever is left in
  <em>start</em> after the long. If the result can not be represented
  by a long, then strtol() returns either <strong>LONG_MAX</strong> or
  <strong>LONG_MIN</strong>. Zero is returned upon error.</p>

  <div class="related-name-format">
    Related topics:
  </div>

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    <a href="atol.html">atol</a><br>
    <a href="strtoul.html">strtoul</a>
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<hr>

  <div class="name-format">
    strtoul
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;stdlib.h&gt;
  unsigned long strtoul( const char *start, char **end, int base );
</pre>

  <p>The function strtoul() behaves exactly like <a href=
  "strtol.html">strtol</a>(), except that it returns an unsigned long
  rather than a mere long.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="strtol.html">strtol</a>
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<hr>

  <div class="name-format">
    strxfrm
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;string.h&gt;
  size_t strxfrm( char *str1, const char *str2, size_t num );
</pre>

  <p>The strxfrm() function manipulates the first <em>num</em>
  characters of <em>str2</em> and stores them in <em>str1</em>. The
  result is such that if a <a href="strcoll.html">strcoll</a>() is
  performed on <em>str1</em> and the old <em>str2</em>, you will get
  the same result as with a <a href="strcmp.html">strcmp</a>().</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="strcmp.html">strcmp</a><br>
    <a href="strcoll.html">strcoll</a>
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<hr>

  <div class="name-format">
    tolower
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;ctype.h&gt;
  int tolower( int ch );
</pre>

  <p>The function tolower() returns the lowercase version of the
  character <em>ch</em>.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="isupper.html">isupper</a><br>
    <a href="toupper.html">toupper</a>
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<hr>

  <div class="name-format">
    toupper
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;ctype.h&gt;
  int toupper( int ch );
</pre>

  <p>The toupper() function returns the uppercase version of the
  character <em>ch</em>.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="tolower.html">tolower</a>
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