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<title>函式范本（Function template）</title>
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<h3><a href="http://caterpillar.onlyfun.net/GossipCN/index.html">From
Gossip@caterpillar</a></h3>
<h1><a href="CppGossip.html">C++
Gossip: 函式范本（Function template）</a></h1>
来看看气泡排序法：<br>
<div style="margin-left: 40px; font-weight: bold; font-family: Courier New,Courier,monospace;">// 整数气泡排序法<br>
</div>
<div style="margin-left: 40px;"><span style="font-weight: bold; font-family: Courier New,Courier,monospace;">void bubbleSort(int number[], int length) { </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> int i, j, k, flag = 1; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">
int tmp; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> for(i = 0; i <
length-1 && flag == 1; i++) { </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> flag = 0; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> for(j =
0; j < length-i-1; j++) { </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> if(number[j+1] < number[j]) {
</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> tmp = number[j]; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> number[j] =
number[j+1]; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> number[j+1] = tmp; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> flag =
1; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> } </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> } </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> } </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">} </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">
// 浮点数气泡排序</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">void bubbleSort(float
number[], int length) { </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> int i, j, k, flag = 1; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> float tmp;
</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> for(i = 0; i < length-1
&& flag == 1; i++) { </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> flag = 0; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> for(j = 0; j <
length-i-1; j++) { </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> if(number[j+1] < number[j]) { </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">
tmp = number[j]; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> number[j] = number[j+1]; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">
number[j+1] = tmp; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> flag = 1; </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> }
</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> } </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;"> } </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">}</span><br>
</div>
<br>
函式范本（Function template）又称“通用函式”（Generic
function），它可以适用于不同资料型态的参数列，但实作内容相同的函式，以上面的气泡排序法为例，除了参数列资料型态不同之外，其实排序的程式码几乎相同，实在没必要为了资料型态的不同而重覆撰写相同的程式码。
<br>
<br>
建立函式范本的方法之一是使用"template"关键字，并使用class来宣告取代用的资料型态宣告字，使用下面这个程式作个示范：<br>
<br>
<pre>#include <iostream> <br>using namespace std; <br><br>template <class X> <br>void bubbleSort(X[], int); <br><br>int main() { <br> int iarr[] = {5, 3, 11, 6, 8, 9, 20, 11}; <br> float farr[] = {5.1, 3.4, 11.3, 6.6, 8.9, 9.11, 20.2, 11.4}; <br><br> bubbleSort(iarr, 8); <br> for(int i = 0; i < 8; i++) <br> cout << " " << iarr[i]; <br> cout << endl; <br><br> bubbleSort(farr, 8); <br> for(int i = 0; i < 8; i++) <br> cout << " " << farr[i]; <br> cout << endl; <br> <br> return 0; <br>} <br><br>template <class X> <br>void bubbleSort(X number[], int length) { <br> int i, j, k, flag = 1; <br> X tmp; <br><br> for(i = 0; i < length-1 && flag == 1; i++) { <br> flag = 0; <br> for(j = 0; j < length-i-1; j++) { <br> if(number[j+1] < number[j]) { <br> tmp = number[j]; <br> number[j] = number[j+1]; <br> number[j+1] = tmp; <br> flag = 1; <br> } <br> } <br> } <br>}</pre>
<span class="postbody"><br>
执行结果：</span><br>
<table style="text-align: left; width: 100%;" border="0" cellpadding="2" cellspacing="2">
<tbody>
<tr>
<td style="background-color: rgb(0, 0, 0);"><small><span style="color: rgb(255, 255, 255);"> 3 5 6 8 9 11 11 20<br>
3.4 5.1 6.6 8.9 9.11 11.3 11.4 20.2</span></small><span style="color: rgb(255, 255, 255);"><br>
</span></td>
</tr>
</tbody>
</table>
<br>
在这个程式中，编译器会自动产生两个版本的bubbleSort()函式，一个是整数阵列的参数，一个是浮点数阵列的参数，也可以使用"typename"来取代class关键字，例如： <br>
<div style="margin-left: 40px; font-family: Courier New,Courier,monospace;"><span style="font-weight: bold;">template <typename X> </span><br style="font-weight: bold;">
<span style="font-weight: bold;">void bubbleSort(X number[], int length) { </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> .... </span><br style="font-weight: bold;">
<span style="font-weight: bold;">}</span><br>
</div>
<br>
"typename"是后来才加入至C++中的，早期的撰写风格主要都是使用"class"。<br>
<br>
在宣告了函式范本之后，您还是可以自行重载函式，例如： <br>
<div style="margin-left: 40px;"><span style="font-weight: bold; font-family: Courier New,Courier,monospace;">template <class X> </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">void bubbleSort(X number[], int length) { </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">....
</span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">} </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">void bubbleSort(int number[], int length, int descend) { </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">//
以descend决定要由大至小或由小至大排序 </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">.... </span><br style="font-weight: bold; font-family: Courier New,Courier,monospace;">
<span style="font-weight: bold; font-family: Courier New,Courier,monospace;">}</span><br>
</div>
<br>
在这个程式片段中，虽然您宣告了样版函式bubbSort()，但您仍自行重载了一个函式以自行定义特定的函式功能。 <br>
<br>
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