1、函数模板
思考：如果重载的函数，其解决问题的逻辑是一致的、函数体语句相同，只是处理的数据类型不同，那么写多个相同的函数体，是重复劳动，而且还可能因为代码的冗余造成不一致性。
解决：使用模板
例：求绝对值函数的模板
主函数如下
int main()
{
int n=-5;
double d=-5.5;
cout<<abs(n)<<endl;
cout<<abs(d)<<endl;
return 0;
}
#include <iostream>
using namespace std;template<typename T>
T abs(T x) {return x < 0? -x : x;
}int main() {int n = -5;double d = -5.5;cout << abs(n) << endl; // 调用 abs<int>cout << abs(d) << endl; // 调用 abs<double>return 0;
}
2、排序函数模板
Description：
已知主函数如程序后缀代码所示，请为其编写适当的模板函数，使主函数的bubbleSort函数可以对一个整型数组和一个浮点数数组进行输入、排序、输出操作。
Sample Input：
无
Sample Output：
#include <iostream>
#include <iomanip>
using namespace std;// 模板函数声明
template <typename T>
void bubbleSort(T arr[], int size);//StudybarCommentBegin
int main()
{ const int arraySize = 10; // size of arrayint a[ arraySize ] = { 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 }, i;// display int array in original ordercout << "Integer data items in original order\n";for ( i = 0; i < arraySize; ++i )cout << setw( 6 ) << a[ i ];bubbleSort( a, arraySize ); // sort the array// display int array in sorted ordercout << "\nInteger data items in ascending order\n";for ( i = 0; i < arraySize; ++i )cout << setw( 6 ) << a[ i ];cout << "\n\n";// initialize double arraydouble b[ arraySize ] = { 10.1, 9.9, 8.8, 7.7, 6.6, 5.5,4.4, 3.3, 2.2, 1.1 };// display double array in original order cout << "double point data items in original order\n";for ( i = 0; i < arraySize; ++i )cout << setw( 6 ) << b[ i ];bubbleSort( b, arraySize ); // sort the array// display sorted double arraycout << "\ndouble point data items in ascending order\n";for ( i = 0; i < arraySize; ++i )cout << setw( 6 ) << b[ i ];cout << endl;return 0;} // end main
//StudybarCommentEnd// 模板函数实现
template <typename T>
void bubbleSort(T arr[], int size) {for (int i = 0; i < size - 1; ++i) {for (int j = 0; j < size - i - 1; ++j) {if (arr[j] > arr[j + 1]) {// 交换元素T temp = arr[j];arr[j] = arr[j + 1];arr[j + 1] = temp;}}}
}
3、重载函数模板printArray
Description：
重载第七章课件10页中的printArray函数模板，代码如下：
#include
using namespace std;
// function template printArray definition
template< typename T >
void printArray( const T *arrayset, int count )
{
for ( int i = 0; i < count && arrayset[i]!=‘\0’ ; i++ )
cout << arrayset[ i ] << " ";
cout << endl;
} // end function template printArray
int main()
{
const int aCount = 5; // size of array a
const int bCount = 7; // size of array b
const int cCount = 6; // size of array c
int a[ aCount ] = { 1, 2, 3, 4, 5 };
double b[ bCount ] = { 1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 7.7 };
char c[ cCount ] = “HELLO”; // 6th position for null
cout << “Array a contains:” << endl;
// call integer function-template specialization
printArray( a, aCount );
cout << “Array b contains:” << endl;
// call double function-template specialization
printArray( b, bCount );
cout << “Array c contains:” << endl;
// call character function-template specialization
printArray( c, cCount );
return 0;
} // end main
重载上述函数模板，使它包含两个额外的名为 int lowSubscript （范围下限）和 int highSubscript（范围上限）的整型参数。调用这个函数会打印出数组中指定范围的元素。函数将判定lowSubscript和highSubscript是否有效，如果超出数组下标范围或highSubscript比lowSubscript小，重载的printArray函数将返回0，否则，返回打印出的元素的个数。然后修改main函数，通过三个数组a、b、c来对两个版本的printArray进行测试。
注：程序后缀代码已给出。
提示：字符’\0’是不可打印字符，因此，cout<<‘\0’; 将导致输出不确定数值。
Sample Input：
无
Sample Output：
#include <iostream>using namespace std;// Original function template printArray definition
template< typename T >
void printArray( const T *arrayset, int count )
{for ( int i = 0; i < count && arrayset[i]!='\0'; i++ )cout << arrayset[ i ] << " ";cout << endl;
} // end function template printArray// Overloaded function template printArray with range parameters
template< typename T >
int printArray( const T *arrayset, int count, int lowSubscript, int highSubscript )
{// Check for invalid subscriptsif (lowSubscript < 0 || highSubscript >= count || lowSubscript > highSubscript) {return 0;}int elementsPrinted = 0;for (int i = lowSubscript; i <= highSubscript; i++) {// For char arrays, don't print null terminatorsif (arrayset[i] != '\0') {cout << arrayset[i] << " ";elementsPrinted++;}}cout << endl;return elementsPrinted;
} // end overloaded function template printArray//StudybarCommentBegin
int main()
{// sizes of arraysconst int aCount = 5;const int bCount = 7;const int cCount = 6;// declare and initialize arraysint a[ aCount ] = { 1, 2, 3, 4, 5 };double b[ bCount ] = { 1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 7.7 };char c[ cCount ] = "HELLO"; // 6th position for nullint elements;// display array a using original printArray functioncout << "\nUsing original printArray function\n";printArray( a, aCount );// display array a using new printArray functioncout << "\nArray a contains:\n";elements = printArray( a, aCount, 0, aCount - 1 );cout << elements << " elements were output\n";// display elements 1-3 of array acout << "Array a from 1 to 3 is:\n";elements = printArray( a, aCount, 1, 3 );cout << elements << " elements were output\n";// try to print an invalid elementcout << "Array a output with invalid subscripts:\n";elements = printArray( a, aCount, -1, 10 );cout << elements << " elements were output\n\n";// display array b using original printArray functioncout << "\nUsing original printArray function\n";printArray( a, aCount );// display array b using new printArray functioncout << "Array b contains:\n";elements = printArray( b, bCount, 0, bCount - 1 );cout << elements << " elements were output\n";// display elements 1-3 of array bcout << "Array b from 1 to 3 is:\n";elements = printArray( b, bCount, 1, 3 );cout << elements << " elements were output\n";// try to print an invalid elementcout << "Array b output with invalid subscripts:\n";elements = printArray( b, bCount, -1, 10 );cout << elements << " elements were output\n\n";// display array c using original printArray functioncout << "\nUsing original printArray function\n";printArray( a, aCount );// display array c using new printArray functioncout << "Array c contains:\n";elements = printArray( c, cCount, 0, cCount - 1 );cout << elements << " elements were output\n";// display elements 1-3 of array ccout << "Array c from 1 to 3 is:\n";elements = printArray( c, cCount, 1, 3 );cout << elements << " elements were output\n";// try to display an invalid elementcout << "Array c output with invalid subscripts:\n";elements = printArray( c, cCount, -1, 10 );cout << elements << " elements were output" << endl;return 0;} // end main
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4、类模板
类模板的作用
使用类模板使用户可以为类声明一种模式，使得类中的某些数据成员、某些成员函数的参数、某些成员函数的返回值，能取任意类型（包括基本类型的和用户自定义类型）。
类模板的声明
类模板 template <模板参数表> class 类名 {类成员声明};
如果需要在类模板以外定义其成员函数，则要采用以下的形式： template <模板参数表> 类型名 类名<模板参数标识符列表>::函数名（参数表）
例9-2 类模板示例
#include <iostream>
#include <cstdlib>
using namespace std;
struct Student {int id; //学号float gpa; //平均分
};
template <class T>
class Store {//类模板：实现对任意类型数据进行存取
private:T item; // item用于存放任意类型的数据bool haveValue; // haveValue标记item是否已被存入内容
public:Store();T &getElem(); //提取数据函数void putElem(const T &x); //存入数据函数
};template <class T>
Store<T>::Store(): haveValue(false) { }
template <class T>
T &Store<T>::getElem() {//如试图提取未初始化的数据，则终止程序if (!haveValue) { cout << "No item present!" << endl;exit(1); //使程序完全退出，返回到操作系统。}return item; // 返回item中存放的数据
}
template <class T>
void Store<T>::putElem(const T &x) {// 将haveValue 置为true，表示item中已存入数值 haveValue = true; item = x; // 将x值存入item
}int main() {Store<int> s1, s2; s1.putElem(3); s2.putElem(-7);cout << s1.getElem() << " " << s2.getElem() << endl;Student g = { 1000, 23 };Store<Student> s3;s3.putElem(g); cout << "The student id is " << s3.getElem().id << endl;Store<double> d;cout << "Retrieving object D... ";cout << d.getElem() << endl;//d未初始化，执行函数D.getElement()时导致程序终止return 0;
}
5、整数集合类
实现整数集合类
要求：1、类中含两个私有变量，集合中元素的个数和集合中元素组成的数组。
2、用Set函数输入，Show函数输出结果（按从小到大的顺序输出各个元素）。3、实现运算符+的重载，表示两个集合的并集。实现运算符&的重载，表示两个集合的交集。实现运算符-的重载，表示两个集合的差。
提示：1、集合中不可出现重复元素。
2、空集时，输出empty。
样例1
输入
3
1 2 3
4
1 2 5 6
输出
1 2 3 5 6
1 2
3
样例2
输入
3
1 2 3
3
1 2 3
输出
1 2 3
1 2 3
empty
#include <iostream>
#include <algorithm>
using namespace std;class Cassemblage {
private:int num;int elements[1000]; // Assuming a maximum size for simplicitypublic:Cassemblage() : num(0) {}void Set(int arr[], int n) {num = 0;for (int i = 0; i < n; ++i) {bool found = false;for (int j = 0; j < num; ++j) {if (elements[j] == arr[i]) {found = true;break;}}if (!found) {elements[num++] = arr[i];}}sort(elements, elements + num);}void Show() {if (num == 0) {cout << "empty";} else {for (int i = 0; i < num; ++i) {cout << elements[i];if (i != num - 1) {cout << " ";}}}}Cassemblage operator+(const Cassemblage& other) const {Cassemblage result;int i = 0, j = 0;while (i < num && j < other.num) {if (elements[i] < other.elements[j]) {if (result.num == 0 || result.elements[result.num - 1] != elements[i]) {result.elements[result.num++] = elements[i];}++i;} else if (elements[i] > other.elements[j]) {if (result.num == 0 || result.elements[result.num - 1] != other.elements[j]) {result.elements[result.num++] = other.elements[j];}++j;} else {if (result.num == 0 || result.elements[result.num - 1] != elements[i]) {result.elements[result.num++] = elements[i];}++i;++j;}}while (i < num) {if (result.num == 0 || result.elements[result.num - 1] != elements[i]) {result.elements[result.num++] = elements[i];}++i;}while (j < other.num) {if (result.num == 0 || result.elements[result.num - 1] != other.elements[j]) {result.elements[result.num++] = other.elements[j];}++j;}return result;}Cassemblage operator&(const Cassemblage& other) const {Cassemblage result;int i = 0, j = 0;while (i < num && j < other.num) {if (elements[i] < other.elements[j]) {++i;} else if (elements[i] > other.elements[j]) {++j;} else {if (result.num == 0 || result.elements[result.num - 1] != elements[i]) {result.elements[result.num++] = elements[i];}++i;++j;}}return result;}Cassemblage operator-(const Cassemblage& other) const {Cassemblage result;int i = 0, j = 0;while (i < num && j < other.num) {if (elements[i] < other.elements[j]) {if (result.num == 0 || result.elements[result.num - 1] != elements[i]) {result.elements[result.num++] = elements[i];}++i;} else if (elements[i] > other.elements[j]) {++j;} else {++i;++j;}}while (i < num) {if (result.num == 0 || result.elements[result.num - 1] != elements[i]) {result.elements[result.num++] = elements[i];}++i;}return result;}
};//StudybarCommentBegin
int main(int argc, char* argv[])
{Cassemblage z1, z2, x1, x2, x3;int i, n1, n2, a1[1000], a2[1000];cin >> n1;for(i=0; i<n1; i++){cin >> a1[i];}z1.Set(a1, n1);cin >> n2;for(i=0; i<n2; i++){cin >> a2[i];} z2.Set(a2, n2);x1=z1+z2;x1.Show();cout << endl;x2=z1&z2;x2.Show();cout << endl;x3=z1-z2;x3.Show();return 0;
}
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