📄 atl under the hood - part 3.mht

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	<SPAN class=3Dcpp-keyword>return</SPAN> a &gt; b ? a : b;
}

<SPAN class=3Dcpp-keyword>class</SPAN> Point {
<SPAN class=3Dcpp-keyword>private</SPAN>:
	<SPAN class=3Dcpp-keyword>int</SPAN> m_x, m_y;

<SPAN class=3Dcpp-keyword>public</SPAN>:
	Point(<SPAN class=3Dcpp-keyword>int</SPAN> p_x =3D <SPAN =
class=3Dcpp-literal>0</SPAN>, <SPAN class=3Dcpp-keyword>int</SPAN> p_y =
=3D <SPAN class=3Dcpp-literal>0</SPAN>) : m_x(p_x), m_y(p_y) {
	}

	<SPAN class=3Dcpp-keyword>bool</SPAN> friend <SPAN =
class=3Dcpp-keyword>operator</SPAN> &gt; (<SPAN =
class=3Dcpp-keyword>const</SPAN> Point&amp; lhs, <SPAN =
class=3Dcpp-keyword>const</SPAN> Point&amp; rhs) {
		<SPAN class=3Dcpp-keyword>return</SPAN> lhs.m_x &gt; rhs.m_x =
&amp;&amp; lhs.m_y &gt; rhs.m_y;
	}

	friend ostream&amp; <SPAN class=3Dcpp-keyword>operator</SPAN> &lt;&lt; =
(ostream&amp; os, <SPAN class=3Dcpp-keyword>const</SPAN> Point&amp; p) {
		<SPAN class=3Dcpp-keyword>return</SPAN> os &lt;&lt; "(" &lt;&lt; p.m_x =
&lt;&lt; ", " &lt;&lt; p.m_y  &lt;&lt; ")";
	}
};

<SPAN class=3Dcpp-keyword>int</SPAN> main() {
	Point a(<SPAN class=3Dcpp-literal>5</SPAN>, <SPAN =
class=3Dcpp-literal>10</SPAN>), b(<SPAN class=3Dcpp-literal>15</SPAN>, =
<SPAN class=3Dcpp-literal>20</SPAN>);
	cout &lt;&lt; Maximum(a, b) &lt;&lt; endl;

	<SPAN class=3Dcpp-keyword>return</SPAN> <SPAN =
class=3Dcpp-literal>0</SPAN>;
}
</PRE>
      <P>The output of this program is</P><PRE lang=3Dtext>(15, =
20)</PRE>
      <P>We can also pass the template class as a template parameter. =
Let's make=20
      this Point class template and pass it as a template parameter to =
Stack=20
      template class.</P>
      <H3>Program 40</H3><PRE><SPAN class=3Dcpp-preprocessor>#include =
&lt;iostream&gt;</SPAN>
using <SPAN class=3Dcpp-keyword>namespace</SPAN> std;

<SPAN class=3Dcpp-keyword>template</SPAN> &lt;<SPAN =
class=3Dcpp-keyword>typename</SPAN> T&gt;
<SPAN class=3Dcpp-keyword>class</SPAN> Point {
<SPAN class=3Dcpp-keyword>private</SPAN>:
	T m_x, m_y;

<SPAN class=3Dcpp-keyword>public</SPAN>:
	Point(T p_x =3D <SPAN class=3Dcpp-literal>0</SPAN>, T p_y =3D <SPAN =
class=3Dcpp-literal>0</SPAN>) : m_x(p_x), m_y(p_y) {
	}

	<SPAN class=3Dcpp-keyword>bool</SPAN> friend <SPAN =
class=3Dcpp-keyword>operator</SPAN> &gt; (<SPAN =
class=3Dcpp-keyword>const</SPAN> Point&lt;T&gt;&amp; lhs, <SPAN =
class=3Dcpp-keyword>const</SPAN> Point&lt;T&gt;&amp; rhs) {
		<SPAN class=3Dcpp-keyword>return</SPAN> lhs.m_x &gt; rhs.m_x =
&amp;&amp; lhs.m_y &gt; rhs.m_y;
	}

	friend ostream&amp; <SPAN class=3Dcpp-keyword>operator</SPAN> &lt;&lt; =
(ostream&amp; os, <SPAN class=3Dcpp-keyword>const</SPAN> =
Point&lt;T&gt;&amp; p) {
		<SPAN class=3Dcpp-keyword>return</SPAN> os &lt;&lt; "(" &lt;&lt; p.m_x =
&lt;&lt; ", " &lt;&lt; p.m_y  &lt;&lt; ")";
	}
};

<SPAN class=3Dcpp-keyword>template</SPAN> &lt;<SPAN =
class=3Dcpp-keyword>typename</SPAN> T, <SPAN =
class=3Dcpp-keyword>int</SPAN> iSize =3D <SPAN =
class=3Dcpp-literal>10</SPAN>&gt;
<SPAN class=3Dcpp-keyword>class</SPAN> Stack {
<SPAN class=3Dcpp-keyword>private</SPAN>:
	T m_pData[iSize];
	<SPAN class=3Dcpp-keyword>int</SPAN> m_iTop;

<SPAN class=3Dcpp-keyword>public</SPAN>:
	Stack() : m_iTop(<SPAN class=3Dcpp-literal>0</SPAN>) {
	}

	<SPAN class=3Dcpp-keyword>void</SPAN> Push(T p_iData) {
		m_pData[m_iTop++] =3D p_iData;
	}

	T Pop() {
		<SPAN class=3Dcpp-keyword>return</SPAN> m_pData[--m_iTop];
	}

	T Top() {
		<SPAN class=3Dcpp-keyword>return</SPAN> m_pData[m_iTop];
	}

<SPAN class=3Dcpp-keyword>private</SPAN>:
	Stack(<SPAN class=3Dcpp-keyword>const</SPAN> Stack&lt;T&gt;&amp;);
	Stack&lt;T&gt;&amp; <SPAN class=3Dcpp-keyword>operator</SPAN> =3D =
(<SPAN class=3Dcpp-keyword>const</SPAN> Stack&lt;T&gt;&amp;);
};

<SPAN class=3Dcpp-keyword>int</SPAN> main() {
	Stack&lt;Point&lt;<SPAN class=3Dcpp-keyword>int</SPAN>&gt; &gt; st;

	st.Push(Point&lt;<SPAN class=3Dcpp-keyword>int</SPAN>&gt;(<SPAN =
class=3Dcpp-literal>5</SPAN>, <SPAN class=3Dcpp-literal>10</SPAN>));
	st.Push(Point&lt;<SPAN class=3Dcpp-keyword>int</SPAN>&gt;(<SPAN =
class=3Dcpp-literal>15</SPAN>, <SPAN class=3Dcpp-literal>20</SPAN>));

	cout &lt;&lt; st.Pop() &lt;&lt; endl;
	cout &lt;&lt; st.Pop() &lt;&lt; endl;

	<SPAN class=3Dcpp-keyword>return</SPAN> <SPAN =
class=3Dcpp-literal>0</SPAN>;
}
</PRE>
      <P>The output of this program is</P><PRE lang=3Dtext>(15, 20)
(5, 10)</PRE>
      <P>The most important part of this program =
is</P><PRE>Stack&lt;Point&lt;<SPAN class=3Dcpp-keyword>int</SPAN>&gt; =
&gt; st;</PRE>
      <P>Here you have to pass the space between the two angle brackets, =
other=20
      wise compiler treat it &gt;&gt; (shift right operator) and =
generate=20
      error.</P>
      <P>There is one more thing we can do with this program. We can =
pass the=20
      default type value of template parameter too. We can change =
</P><PRE><SPAN class=3Dcpp-keyword>template</SPAN> &lt;<SPAN =
class=3Dcpp-keyword>typename</SPAN> T, <SPAN =
class=3Dcpp-keyword>int</SPAN> iSize =3D <SPAN =
class=3Dcpp-literal>10</SPAN>&gt;</PRE>to=20
<PRE><SPAN class=3Dcpp-keyword>template</SPAN> &lt;<SPAN =
class=3Dcpp-keyword>typename</SPAN> T =3D <SPAN =
class=3Dcpp-keyword>int</SPAN>, <SPAN class=3Dcpp-keyword>int</SPAN> =
iSize =3D <SPAN class=3Dcpp-literal>10</SPAN>&gt;</PRE>
      <P>Now we don't have to pass the data type at the time of creating =
the=20
      object from Stack class. But you have to write the blank angle =
brackets at=20
      the time of creating the object to order the compiler to use =
default data=20
      type. You will create object something like =
this.</P><PRE>Stack&lt;&gt; st;</PRE>
      <P>When you declare template class member function outside the =
class then=20
      you have to give the complete name of template class with its =
Template=20
      parameter.</P>
      <H3>Program 41</H3><PRE><SPAN class=3Dcpp-preprocessor>#include =
&lt;iostream&gt;</SPAN>
using <SPAN class=3Dcpp-keyword>namespace</SPAN> std;

<SPAN class=3Dcpp-keyword>template</SPAN> &lt;<SPAN =
class=3Dcpp-keyword>typename</SPAN> T&gt;
<SPAN class=3Dcpp-keyword>class</SPAN> Point {
<SPAN class=3Dcpp-keyword>private</SPAN>:
	T m_x, m_y;

<SPAN class=3Dcpp-keyword>public</SPAN>:
	Point(T p_x =3D <SPAN class=3Dcpp-literal>0</SPAN>, T p_y =3D <SPAN =
class=3Dcpp-literal>0</SPAN>);
	<SPAN class=3Dcpp-keyword>void</SPAN> Setxy(T p_x, T p_y);
	T getX() <SPAN class=3Dcpp-keyword>const</SPAN>;
	T getY() <SPAN class=3Dcpp-keyword>const</SPAN>;

	friend ostream&amp; <SPAN class=3Dcpp-keyword>operator</SPAN> &lt;&lt; =
(ostream&amp; os, <SPAN class=3Dcpp-keyword>const</SPAN> =
Point&lt;T&gt;&amp; p) {
		<SPAN class=3Dcpp-keyword>return</SPAN> os &lt;&lt; "(" &lt;&lt; p.m_x =
&lt;&lt; ", " &lt;&lt; p.m_y  &lt;&lt; ")";
	}
};

<SPAN class=3Dcpp-keyword>template</SPAN> &lt;<SPAN =
class=3Dcpp-keyword>typename</SPAN> T&gt;
Point&lt;T&gt;::Point(T p_x, T p_y) : m_x(p_x), m_y(p_y) {
}

<SPAN class=3Dcpp-keyword>template</SPAN> &lt;<SPAN =
class=3Dcpp-keyword>typename</SPAN> T&gt;
<SPAN class=3Dcpp-keyword>void</SPAN> Point&lt;T&gt;::Setxy(T p_x, T =
p_y) {
	m_x =3D p_x;
	m_y =3D p_y;
}

<SPAN class=3Dcpp-keyword>template</SPAN> &lt;<SPAN =
class=3Dcpp-keyword>typename</SPAN> T&gt;
T Point&lt;T&gt;::getX() <SPAN class=3Dcpp-keyword>const</SPAN> {
	<SPAN class=3Dcpp-keyword>return</SPAN> m_x;
}

<SPAN class=3Dcpp-keyword>template</SPAN> &lt;<SPAN =
class=3Dcpp-keyword>typename</SPAN> T&gt;
T Point&lt;T&gt;::getY() <SPAN class=3Dcpp-keyword>const</SPAN> {
	<SPAN class=3Dcpp-keyword>return</SPAN> m_y;
}

<SPAN class=3Dcpp-keyword>int</SPAN> main() {
	Point&lt;<SPAN class=3Dcpp-keyword>int</SPAN>&gt; p;
	p.Setxy(<SPAN class=3Dcpp-literal>20</SPAN>, <SPAN =
class=3Dcpp-literal>30</SPAN>);
	cout &lt;&lt; p &lt;&lt; endl;

	<SPAN class=3Dcpp-keyword>return</SPAN> <SPAN =
class=3Dcpp-literal>0</SPAN>;
}
</PRE>
      <P>The output of the program is </P><PRE lang=3Dtext>(20, =
30)</PRE>
      <P>Lets change program 35 little bit and pass string value rather =
than int=20
      or float and see the result.</P>
      <H3>Program 42</H3><PRE><SPAN class=3Dcpp-preprocessor>#include =
&lt;iostream&gt;</SPAN>
using <SPAN class=3Dcpp-keyword>namespace</SPAN> std;

<SPAN class=3Dcpp-keyword>template</SPAN> &lt;<SPAN =
class=3Dcpp-keyword>typename</SPAN> T&gt;
T Maximum(T a, T b) {
	<SPAN class=3Dcpp-keyword>return</SPAN> a &gt; b ? a : b;
}

<SPAN class=3Dcpp-keyword>int</SPAN> main() {
	cout &lt;&lt; Maximum("Pakistan", "Karachi") &lt;&lt; endl;
=09
	<SPAN class=3Dcpp-keyword>return</SPAN> <SPAN =
class=3Dcpp-literal>0</SPAN>;
}
</PRE>
      <P>The output of this program is Karachi. Why? Because here char* =
is=20
      passed as a template parameter. Karachi is stored at higher memory =

      location so the &gt; operator just compare the value of address =
rather=20
      then the string itself.</P>
      <P>What should we do if we want the comparison on the basis of =
length of=20
      string not on the basis of their address?</P>
      <P>The solution is to specialized the template on char* data type. =
Here is=20
      an example of template specialization.</P>
      <H3>Program 43</H3><PRE><SPAN class=3Dcpp-preprocessor>#include =
&lt;iostream&gt;</SPAN>
using <SPAN class=3Dcpp-keyword>namespace</SPAN> std;

<SPAN class=3Dcpp-keyword>template</SPAN> &lt;<SPAN =
class=3Dcpp-keyword>typename</SPAN> T&gt;
T Maximum(T a, T b) {
	<SPAN class=3Dcpp-keyword>return</SPAN> a &gt; b ? a : b;
}

<SPAN class=3Dcpp-keyword>template</SPAN> &lt;&gt;
<SPAN class=3Dcpp-keyword>char</SPAN>* Maximum(<SPAN =
class=3Dcpp-keyword>char</SPAN>* a, <SPAN =
class=3Dcpp-keyword>char</SPAN>* b) {
	<SPAN class=3Dcpp-keyword>return</SPAN> strlen(a) &gt; strlen(b) ? a : =
b;
}

<SPAN class=3Dcpp-keyword>int</SPAN> main() {
	cout &lt;&lt; Maximum("Pakistan", "Karachi") &lt;&lt; endl;
=09
	<SPAN class=3Dcpp-keyword>return</SPAN> <SPAN =
class=3Dcpp-literal>0</SPAN>;
}
</PRE>
      <P>Classes can be specialized in the same way. </P>.=20
      <H3>Program 44</H3><PRE><SPAN class=3Dcpp-preprocessor>#include =
&lt;iostream&gt;</SPAN>
using <SPAN class=3Dcpp-keyword>namespace</SPAN> std;

<SPAN class=3Dcpp-keyword>template</SPAN> &lt;<SPAN =
class=3Dcpp-keyword>typename</SPAN> T&gt;
<SPAN class=3Dcpp-keyword>class</SPAN> TestClass {
<SPAN class=3Dcpp-keyword>public</SPAN>:
	<SPAN class=3Dcpp-keyword>void</SPAN> F(T pT) {
		cout &lt;&lt; "T version" &lt;&lt; <SPAN =
class=3Dcpp-string>'\t'</SPAN>;
		cout &lt;&lt; pT &lt;&lt; endl;
	}
};

<SPAN class=3Dcpp-keyword>template</SPAN> &lt;&gt;
<SPAN class=3Dcpp-keyword>class</SPAN> TestClass&lt;<SPAN =
class=3Dcpp-keyword>int</SPAN>&gt; {
<SPAN class=3Dcpp-keyword>public</SPAN>:
	<SPAN class=3Dcpp-keyword>void</SPAN> F(<SPAN =
class=3Dcpp-keyword>int</SPAN> pT) {
		cout &lt;&lt; "<SPAN class=3Dcpp-keyword>int</SPAN> version" &lt;&lt; =
<SPAN class=3Dcpp-string>'\t'</SPAN>;
		cout &lt;&lt; pT &lt;&lt; endl;
	}
};

<SPAN class=3Dcpp-keyword>int</SPAN> main() {
	TestClass&lt;<SPAN class=3Dcpp-keyword>char</SPAN>&gt; obj1;
	TestClass&lt;<SPAN class=3Dcpp-keyword>int</SPAN>&gt; obj2;

	obj1.F(<SPAN class=3Dcpp-string>'A'</SPAN>);
	obj2.F(<SPAN class=3Dcpp-literal>10</SPAN>);

	<SPAN class=3Dcpp-keyword>return</SPAN> <SPAN =
class=3Dcpp-literal>0</SPAN>;
}
</PRE>
      <P>The output of this program is</P><PRE lang=3Dtext>T version	A
int version	10</PRE>
      <P>ATL has several classes which have specialized version like =
this, such=20
      as CComQIPtr define in ATLBASE.H</P>
      <P>Template can also be used in different design patter. E.g. =
Strategy=20
      design pattern can be implemented by using template.</P>
      <H3>Program 45</H3><PRE><SPAN class=3Dcpp-preprocessor>#include =
&lt;iostream&gt;</SPAN>
using <SPAN class=3Dcpp-keyword>namespace</SPAN> std;

<SPAN class=3Dcpp-keyword>class</SPAN> Round1 {
<SPAN class=3Dcpp-keyword>public</SPAN>:
	<SPAN class=3Dcpp-keyword>void</SPAN> Play() {
		cout &lt;&lt; "Round1::Play" &lt;&lt; endl;
	}
};

<SPAN class=3Dcpp-keyword>class</SPAN> Round2 {
<SPAN class=3Dcpp-keyword>public</SPAN>:
	<SPAN class=3Dcpp-keyword>void</SPAN> Play() {
		cout &lt;&lt; "Round2::Play" &lt;&lt; endl;
	}
};

<SPAN class=3Dcpp-keyword>template</SPAN> &lt;<SPAN =
class=3Dcpp-keyword>typename</SPAN> T&gt;
<SPAN class=3Dcpp-keyword>class</SPAN> Strategy {
<SPAN class=3Dcpp-keyword>private</SPAN>:
	T objT;
<SPAN class=3Dcpp-keyword>public</SPAN>:
	<SPAN class=3Dcpp-keyword>void</SPAN> Play() {
		objT.Play();
	}
};

<SPAN class=3Dcpp-keyword>int</SPAN> main() {
	Strategy&lt;Round1&gt; obj1;
	Strategy&lt;Round2&gt; obj2;
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