subject_65475.htm

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序号：65475 发表者：由零开始 发表日期：2003-12-17 21:03:41
<br>主题：请问这个友元函数为何不能访问私有成员？？？
<br>内容：//mystring.h<BR><BR>#include &lt;iostream&gt;<BR>using namespace std;<BR><BR>class String;<BR>istream&amp; operator&gt;&gt;( istream &amp;, String &amp; );<BR>ostream&amp; operator&lt;&lt;( ostream &amp;, const String &amp; );<BR><BR>class String<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;friend bool operator==( const String &amp;, const String &amp; );<BR>&nbsp;&nbsp;&nbsp;&nbsp;friend bool operator==( const char *, const String &amp; );<BR>&nbsp;&nbsp;&nbsp;&nbsp;friend bool operator==( const String &amp;, const char * );<BR>public:<BR>&nbsp;&nbsp;&nbsp;&nbsp;//构造和析构<BR>&nbsp;&nbsp;&nbsp;&nbsp;String( const char* = 0 );<BR>&nbsp;&nbsp;&nbsp;&nbsp;String( const String &amp; );<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;~String();<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;//赋值操作符的重载集合<BR>&nbsp;&nbsp;&nbsp;&nbsp;String&amp; operator=( const String &amp; );<BR>&nbsp;&nbsp;&nbsp;&nbsp;String&amp; operator=( const char * );<BR>&nbsp;&nbsp;&nbsp;&nbsp;String&amp; operator+=( const String &amp; );<BR>&nbsp;&nbsp;&nbsp;&nbsp;String&amp; operator+=( const char * );<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;//重载的下标操作符<BR>&nbsp;&nbsp;&nbsp;&nbsp;char&amp; operator[]( int ) const;<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;//等于操作符的重载集合<BR>&nbsp;&nbsp;&nbsp;&nbsp;//str1 == str2;<BR>&nbsp;&nbsp;&nbsp;&nbsp;bool operator==( const char * ) const;<BR>&nbsp;&nbsp;&nbsp;&nbsp;bool operator==( const String &amp; ) const;<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;//成员访问函数<BR>&nbsp;&nbsp;&nbsp;&nbsp;int size() { return _size; }<BR>&nbsp;&nbsp;&nbsp;&nbsp;char* c_str() { return _string; }<BR><BR>private:<BR>&nbsp;&nbsp;&nbsp;&nbsp;int _size;<BR>&nbsp;&nbsp;&nbsp;&nbsp;char *_string;<BR>};<BR><BR>///////////////////////////////////////////////////////////////////////////<BR>//string.cpp<BR><BR>#include &lt;iostream&gt;<BR>#include &#34;mystring.h&#34;<BR>using namespace std;<BR><BR>inline String&amp; String::operator += ( const String &amp;rhs )<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;//如果rhs应用的String不为空<BR>&nbsp;&nbsp;&nbsp;&nbsp;if( rhs._string )<BR>&nbsp;&nbsp;&nbsp;&nbsp;{<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;String tmp( *this );<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//创建足够大的存储区<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//以便包含被连接之后的String<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;_size += rhs._size;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;delete [] _string;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;_string = new char[ _size + 1 ];<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//首先，把原来的String拷贝到新的存储区中<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//然后附加上rhs所指的String<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;strcpy( _string, tmp._string );<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;strcpy( _string + tmp._size, rhs._string );<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;return *this;<BR>}<BR><BR>inline String&amp; String::operator += ( const char *s )<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;//如果rhs应用的String不为空<BR>&nbsp;&nbsp;&nbsp;&nbsp;if( s )<BR>&nbsp;&nbsp;&nbsp;&nbsp;{<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;String tmp( *this );<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//创建足够大的存储区<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//以便包含被连接之后的String<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;_size += strlen( s );<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;delete [] _string;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;_string = new char[ _size + 1 ];<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//首先，把原来的String拷贝到新的存储区中<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//然后附加上rhs所指的String<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;strcpy( _string, tmp._string );<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;strcpy( _string + tmp._size, s );<BR>&nbsp;&nbsp;&nbsp;&nbsp;}<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;return *this;<BR>}<BR><BR>bool String::operator==( const String &amp;rhs ) const<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;if( _size != rhs._size )<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return false;<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;return strcmp( _string, rhs._string ) ? false : true;<BR>}<BR><BR><BR>/* 错误在这个函数里面！！！！！！*/<BR>bool operator==( const String&amp; str1, const String &amp;str2 )<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;if( str1._size != str2._size )<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return false;<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;return strcmp( str1._string, str2._string ) ? false : true;<BR>}<BR><BR>int main()<BR>{<BR>&nbsp;&nbsp;&nbsp;&nbsp;String myStr;<BR>&nbsp;&nbsp;&nbsp;&nbsp;myStr = &#34;Sherlock&#34;;<BR><BR>&nbsp;&nbsp;&nbsp;&nbsp;return 0;<BR>}<BR><BR><BR>编译提示：<BR><BR>Compiling...<BR>string.cpp<BR>F:\LJL\CPPPRIMER\string.cpp(60) : error C2248: '_size' : cannot access private member declared in class 'String'<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;f:\ljl\cppprimer\mystring.h(39) : see declaration of '_size'<BR>F:\LJL\CPPPRIMER\string.cpp(60) : error C2248: '_size' : cannot access private member declared in class 'String'<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;f:\ljl\cppprimer\mystring.h(39) : see declaration of '_size'<BR>F:\LJL\CPPPRIMER\string.cpp(63) : error C2248: '_string' : cannot access private member declared in class 'String'<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;f:\ljl\cppprimer\mystring.h(40) : see declaration of '_string'<BR>F:\LJL\CPPPRIMER\string.cpp(63) : error C2248: '_string' : cannot access private member declared in class 'String'<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;f:\ljl\cppprimer\mystring.h(40) : see declaration of '_string'<BR>Error executing cl.exe.<BR><BR>string.obj - 4 error(s), 0 warning(s)
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<font color=red>答案被接受</font><br>回复者：Cxt_ann 回复日期：2003-12-17 21:32:16
<br>内容：问题很多：首先，你使用了strcpy等函数，却没有包含#include &lt;cstring&gt;<BR>还有，既然你在类中声明了析构函数，不管他工作不工作，都要定义：<BR>String :: ~String()<BR>{}<BR>另外，你在类声明中声明了构造函数，为什么不定义，出错！<BR>2003-12-17 21:46:36