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C语言字符串库函数 | 雅乐网 </title>
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<ul id="content-index-contents"><li class="content-index-level-1"><a href="http://www.yalewoo.com/c_string_h-2.html#字符串长度" title="字符串长度"><em>1</em><span>字符串长度</span></a><ul class="children"><li class="content-index-level-2"><a href="http://www.yalewoo.com/c_string_h-2.html#size_t strlen( const char *str );" title="size_t strlen( const char *str );"><em>1.1</em><span>size_t strlen( const char *str );</span></a></li></ul></li><li class="content-index-level-1"><a href="http://www.yalewoo.com/c_string_h-2.html#字符串比较函数" title="字符串比较函数"><em>2</em><span>字符串比较函数</span></a><ul class="children"><li class="content-index-level-2"><a href="http://www.yalewoo.com/c_string_h-2.html#int strcmp( const char *lhs, const char *rhs );" title="int strcmp( const char *lhs, const char *rhs );"><em>2.1</em><span>int strcmp( const char *lhs, const char *rhs );</span></a></li><li class="content-index-level-2"><a href="http://www.yalewoo.com/c_string_h-2.html#int strncmp( const char *lhs, const char *rhs, size_t count );" title="int strncmp( const char *lhs, const char *rhs, size_t count );"><em>2.2</em><span>int strncmp( const char *lhs, const char *rhs, size_t count );</span></a></li></ul></li><li class="content-index-level-1"><a href="http://www.yalewoo.com/c_string_h-2.html#字符串复制" title="字符串复制"><em>3</em><span>字符串复制</span></a><ul class="children"><li class="content-index-level-2"><a href="http://www.yalewoo.com/c_string_h-2.html#char *strcpy( char *dest, const char *src );" title="char *strcpy( char *dest, const char *src );"><em>3.1</em><span>char *strcpy( char *dest, const char *src );</span></a></li><li class="content-index-level-2"><a href="http://www.yalewoo.com/c_string_h-2.html#char *strncpy( char *dest, const char *src, size_t count );" title="char *strncpy( char *dest, const char *src, size_t count );"><em>3.2</em><span>char *strncpy( char *dest, const char *src, size_t count );</span></a></li></ul></li><li class="content-index-level-1"><a href="http://www.yalewoo.com/c_string_h-2.html# 字符串拼接函数" title=" 字符串拼接函数"><em>4</em><span> 字符串拼接函数</span></a><ul class="children"><li class="content-index-level-2"><a href="http://www.yalewoo.com/c_string_h-2.html#char *strcat( char *dest, const char *src );" title="char *strcat( char *dest, const char *src );"><em>4.1</em><span>char *strcat( char *dest, const char *src );</span></a></li><li class="content-index-level-2"><a href="http://www.yalewoo.com/c_string_h-2.html#char *strncat( char *dest, const char *src, size_t count );" title="char *strncat( char *dest, const char *src, size_t count );"><em>4.2</em><span>char *strncat( char *dest, const char *src, size_t count );</span></a></li></ul></li><li class="content-index-level-1"><a href="http://www.yalewoo.com/c_string_h-2.html#“万能”函数sprintf" title="“万能”函数sprintf"><em>5</em><span>“万能”函数sprintf</span></a><ul class="children"><li class="content-index-level-2"><a href="http://www.yalewoo.com/c_string_h-2.html#int sprintf( char *buffer, const char *format, … );" title="int sprintf( char *buffer, const char *format, … );"><em>5.1</em><span>int sprintf( char *buffer, const char *format, … );</span></a></li></ul></li></ul></div>
<p>C语言标准提供了许多处理字符串的函数。</p>
<h3 id="字符串长度">字符串长度</h3>
<h4 id="size_t strlen( const char *str );">size_t strlen( const char *str );</h4>
<p>strlen函数返回字符串的长度，不包括’\0′</p>
<p>也就是从str指向的字符开始向后数，遇到’\0’就会结束。</p>
<p>例如”Hello”字符串长度是5.</p>
<h3 id="字符串比较函数">字符串比较函数</h3>
<h4 id="int strcmp( const char *lhs, const char *rhs );">int strcmp( const char *lhs, const char *rhs );</h4>
<p>strcmp函数比较lhs和rhs两个字符串，按照字典中的顺序，返回值是 <strong>第一个字符串 – 第二个字符串</strong></p>
<p>如果返回值是0，则两个字符串相等。</p>
<p>如果返回值是正数，则第一个字符串在字典中（机器编码）在第二个字符串后面。</p>
<p>如果返回值是负数，则第一个字符串在字典中（机器编码）在第二个字符串前面。</p>
<p>如果两个字符串开始的字母相等，则会继续下一个字母，一直到两边不匹配 或者 某一个字符串遇到’\0’为止。</p>
<h4 id="int strncmp( const char *lhs, const char *rhs, size_t count );">int strncmp( const char *lhs, const char *rhs, size_t count );</h4>
<p>多加了一个参数count，指定比较前count个字符。</p>
<h3 id="字符串复制">字符串复制</h3>
<h4 id="char *strcpy( char *dest, const char *src );">char *strcpy( char *dest, const char *src );</h4>
<p>将src指向的字符串复制到dest指向的地址，包括最后的’\0′ 。如果src很长（一直遇不到’\0’），则会发生未知结果。</p>
<p>注意：必须给dest指向的地方分配内存。</p>
<p>返回值：strcpy的返回值是第一个参数dest的值。</p>
<h4 id="char *strncpy( char *dest, const char *src, size_t count );">char *strncpy( char *dest, const char *src, size_t count );</h4>
<p>strncpy第三个参数 指定最多复制多少个字符。</p>
<p>如果src的长度小于count ，则该函数作用和strcpy相同。</p>
<p>如果src的长度大于count，则会将src的前count个字符复制进dest，这时dest末尾没有结束符’\0′.因此经常用这种形式</p>
<div id="crayon-5a4560fc838f7487901766" class="crayon-syntax crayon-theme-classic crayon-font-consolas crayon-os-pc print-yes notranslate" data-settings=" minimize scroll-mouseover disable-anim wrap" style=" margin-top: 12px; margin-bottom: 12px; font-size: 20px !important; line-height: 30px !important;">
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strncpy(dest, src, count);
dest[count] = '\0';</textarea></div>
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<td class="crayon-nums " data-settings="show">
<div class="crayon-nums-content" style="font-size: 20px !important; line-height: 30px !important;"><div class="crayon-num" data-line="crayon-5a4560fc838f7487901766-1">1</div><div class="crayon-num" data-line="crayon-5a4560fc838f7487901766-2">2</div></div>
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<td class="crayon-code"><div class="crayon-pre" style="font-size: 20px !important; line-height: 30px !important; -moz-tab-size:4; -o-tab-size:4; -webkit-tab-size:4; tab-size:4;"><div class="crayon-line" id="crayon-5a4560fc838f7487901766-1"><span class="crayon-e">strncpy</span><span class="crayon-sy">(</span><span class="crayon-v">dest</span><span class="crayon-sy">,</span><span class="crayon-h"> </span><span class="crayon-v">src</span><span class="crayon-sy">,</span><span class="crayon-h"> </span><span class="crayon-v">count</span><span class="crayon-sy">)</span><span class="crayon-sy">;</span></div><div class="crayon-line" id="crayon-5a4560fc838f7487901766-2"><span class="crayon-v">dest</span><span class="crayon-sy">[</span><span class="crayon-v">count</span><span class="crayon-sy">]</span><span class="crayon-h"> </span><span class="crayon-o">=</span><span class="crayon-h"> </span><span class="crayon-s">'\0'</span><span class="crayon-sy">;</span></div></div></td>
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</table>
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</div><p></p>
<h3 id=" 字符串拼接函数"> 字符串拼接函数</h3>
<h4 id="char *strcat( char *dest, const char *src );">char *strcat( char *dest, const char *src );</h4>
<p>strcat函数将src处的字符串复制到dest字符串的结尾后面（即dest字符串后面的’\0’处）。</p>
<h4 id="char *strncat( char *dest, const char *src, size_t count );">char *strncat( char *dest, const char *src, size_t count );</h4>
<p>多了一个参数count指定最多在dest末尾加上多少个字符。</p>
<h3 id="“万能”函数sprintf">“万能”函数sprintf</h3>
<h4 id="int sprintf( char *buffer, const char *format, … );">int sprintf( char *buffer, const char *format, … );</h4>
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