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It is provided "as is" without express or implied warranty. -- --><Head><Title>mem_fun_t<Result, X></Title><!-- Generated by htmldoc --></HEAD><BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b" ALINK="#ff0000"> <IMG SRC="CorpID.gif" ALT="SGI" HEIGHT="43" WIDTH="151"> <!--end header--><BR Clear><H1>mem_fun_t<Result, X></H1><Table CellPadding=0 CellSpacing=0 width=100%><TR><TD Align=left><Img src = "functors.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD><TD Align=right><Img src = "type.gif" Alt="" WIDTH = "194" HEIGHT = "39" ></TD></TR><TR><TD Align=left><Img src = "adaptors.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD><TD Align=right></TD></TR><TR><TD Align=left VAlign=top><b>Categories</b>: functors, adaptors</TD><TD Align=right VAlign=top><b>Component type</b>: type</TD></TR></Table><h3>Description</h3><tt>Mem_fun_t</tt> is an adaptor for member functions. If <tt>X</tt> is some class with a member function <tt>Result X::f()</tt> (that is, a member function that takes no arguments and that returns a value oftype <tt>Result</tt> <A href="#1">[1]</A>), then a <tt>mem_fun_t<Result, X></tt> is a <A href="functors.html">function object</A>adaptor that makes it possible to call <tt>f()</tt> as if it were an ordinary function instead of a member function.<P><tt>Mem_fun_t<Result, X></tt>'s constructor takes a pointer to one of <tt>X</tt>'s member functions. Then, like all function objects, <tt>mem_fun_t</tt> has an <tt>operator()</tt> that allows the <tt>mem_fun_t</tt>to be invoked with ordinary function call syntax. In this case,<tt>mem_fun_t</tt>'s <tt>operator()</tt> takes an argument of type <tt>X*</tt>. <P>If <tt>F</tt> is a <tt>mem_fun_t</tt> that was constructed to use the memberfunction <tt>X::f</tt>, and if <tt>x</tt> is a pointer of type <tt>X*</tt>, then theexpression <tt>F(x)</tt> is equivalent to the expression <tt>x->f()</tt>. Thedifference is simply that <tt>F</tt> can be passed to STL algorithms whosearguments must be function objects.<P><tt>Mem_fun_t</tt> is one of a family of member function adaptors. These adaptors are useful if you want to combine generic programmingwith inheritance and polymorphism, since, in C++, polymorphisminvolves calling member functions through pointers or references.<P>As with many other adaptors, it is usually inconvenient to use <tt>mem_fun_t</tt>'s constructor directly. It is usually better to usethe helper function <tt>mem_fun</tt> instead.<h3>Example</h3><pre>struct B { virtual void print() = 0;};struct D1 : public B { void print() { cout << "I'm a D1" << endl; }};struct D2 : public B { void print() { cout << "I'm a D2" << endl; }};int main(){ <A href="Vector.html">vector</A><B*> V; V.push_back(new D1); V.push_back(new D2); V.push_back(new D2); V.push_back(new D1); <A href="for_each.html">for_each</A>(V.begin(), V.end(), mem_fun(&B::print));}</pre><h3>Definition</h3>Defined in the standard header <A href="functional">functional</A>, and in the nonstandardbackward-compatibility header <A href="function.h">function.h</A>.<h3>Template parameters</h3><Table border><TR><TH>Parameter</TH><TH>Description</TH><TH>Default</TH></TR><TR><TD VAlign=top><tt>Result</tt></TD><TD VAlign=top>The member function's return type.</TD><TD VAlign=top> </TD></TR><TR><TD VAlign=top><tt>X</tt></TD><TD VAlign=top>The class whose member function the <tt>mem_fun_t</tt> invokes.</TD><TD VAlign=top> </TD></tr></table><h3>Model of</h3><A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A><h3>Type requirements</h3><UL><LI><tt>X</tt> has at least one member function that takes no arguments and that returns a value of type <tt>Result</tt>. <A href="#1">[1]</A></UL><h3>Public base classes</h3><tt><A href="unary_function.html">unary_function</A><X*, Result></tt><h3>Members</h3><Table border><TR><TH>Member</TH><TH>Where defined</TH><TH>Description</TH></TR><TR><TD VAlign=top><tt>argument_type</tt></TD><TD VAlign=top> <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A></TD><TD VAlign=top>The type of the argument: <tt>X*</tt></TD></TR><TR><TD VAlign=top><tt>result_type</tt></TD><TD VAlign=top> <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A></TD><TD VAlign=top>The type of the result: <tt>Result</tt></TD></TR><TR><TD VAlign=top><pre>Result operator()(X* x) const</pre></TD><TD VAlign=top> <A href="UnaryFunction.html">Unary Function</A></TD><TD VAlign=top>Function call operator. Invokes <tt>x->f()</tt>, where <tt>f</tt> is the member function that was passed to the constructor.</TD></TR><TR><TD VAlign=top><pre>explicit mem_fun_t(Result (X::*f)())</pre></TD><TD VAlign=top><tt>mem_fun_t</tt></TD><TD VAlign=top>See below.</TD></TR><TR><TD VAlign=top><pre>template <class Result, class X>mem_fun_t<Result, X>mem_fun(Result (X::*f)());</pre></TD><TD VAlign=top><tt>mem_fun_t</tt></TD><TD VAlign=top>See below.</TD></tr></table><h3>New members</h3>These members are not defined in the <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A>requirements, but are specific to <tt>mem_fun_t</tt>.<Table border><TR><TH>Member</TH><TH>Description</TH></TR><TR><TD VAlign=top><pre>explicit mem_fun_t(Result (X::*f)())</pre></TD><TD VAlign=top>The constructor. Creates a <tt>mem_fun_t</tt> that calls the member function <tt>f</tt>.</TD></TR><TR><TD VAlign=top><pre>template <class Result, class X>mem_fun_t<Result, X>mem_fun(Result (X::*f)());</pre></TD><TD VAlign=top>If <tt>f</tt> if of type <tt>Result (X::*)</tt> then <tt>mem_fun(f)</tt> is thesame as <tt>mem_fun_t<Result, X>(f)</tt>, but is more convenient. This is aglobal function, not a member function.</TD></tr></table><h3>Notes</h3><P><A name="1">[1]</A>The type <tt>Result</tt> is permitted to be <tt>void</tt>. That is, thisadaptor may be used for functions that return no value. However, thispresents implementation difficulties. According to the draft C++standard, it is possible to return from a <tt>void</tt> function by writing<tt>return void</tt> instead of just <tt>return</tt>. At present, however (early1998), very few compilers support that feature. As a substitute,then, <tt>mem_fun_t</tt> uses partial specialization to support <tt>void</tt> memberfunctions. If your compiler has not implemented partialspecialization, then you will not be able to use <tt>mem_fun_t</tt> withmember functions whose return type is <tt>void</tt>.<h3>See also</h3><tt><A href="mem_fun_ref_t.html">mem_fun_ref_t</A></tt>, <tt><A href="mem_fun1_t.html">mem_fun1_t</A></tt>, <tt><A href="mem_fun1_ref_t.html">mem_fun1_ref_t</A></tt><!--start footer--> <HR SIZE="6"><A href="http://www.sgi.com/"><IMG SRC="surf.gif" HEIGHT="54" WIDTH="54" ALT="[Silicon Surf]"></A><A HREF="index.html"><IMG SRC="stl_home.gif" HEIGHT="54" WIDTH="54" ALT="[STL Home]"></A><BR><FONT SIZE="-2"><A href="http://www.sgi.com/Misc/sgi_info.html" TARGET="_top">Copyright © 1999 Silicon Graphics, Inc.</A> All Rights Reserved.</FONT><FONT SIZE="-3"><a href="http://www.sgi.com/Misc/external.list.html" TARGET="_top">TrademarkInformation</A></FONT><P></BODY></HTML> ⌨️ 快捷键说明
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