模板特製化
模板特製化template specialization
語法
template <>
由template後面再加上尖括號<>，告知編譯器以下模板是有指定類型，參數類型都有符合才會執行。
函式模板
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#include <iostream>
using namespace std;
// 模板名為getMax，傳回類型為模板形參T，參數名為a與b
template <typename T>
T getMax(T a, T b) {
if(a > b)
return a; // 若a比較大就把a傳回去
else
return b; // 若b比較大就把b傳回去。
}
int main() {
int a = 10;
int b = 20;
int max = getMax(a,b);
cout << "max = " << max << endl;
return 0;
}
max = 20
模板特製化
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#include <iostream>
using namespace std;
class Student {
public:
void setScore(int score) {
this->score = score;
}
int getScore() {
return this->score;
}
private:
int score;
};
// 函式模板
template <typename T>
T getMax(T a, T b) {
if(a > b)
return a;
else
return b;
}
// 模板特製化
template <>
Student getMax<Student>(Student s1, Student s2) {
if(s1.getScore() > s2.getScore())
return s1;
else
return s2;
}
int main() {
int a = 10;
int b = 20;
int max = getMax(a,b);
cout << "max = " << max << endl;
Student s1;
s1.setScore(78);
cout << "s1 score = " << s1.getScore() << endl;
Student s2;
s2.setScore(50);
cout << "s2 score = " << s2.getScore() << endl;
// 呼叫模板特製化
Student rtn = getMax(s1, s2);
cout << "score = " << rtn.getScore()<< endl;
return 0;
}
max = 20
s1 score = 78
s2 score = 50
score = 78
模板函式與特製化函式傳回值與參數要一致
若模板函式是使用T，特製化模板也要使用類型。若模板函式是使用T&，特製化模板則是使用類型參考&。否則若不一致，例:模板函式用T，特製化模板用類型參考&，將會產生錯誤error: no function template matches function template specialization。
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#include <iostream>
using namespace std;
class Student {
public:
void setScore(int score) {
this->score = score;
}
int getScore() {
return this->score;
}
private:
int score;
};
template <typename T>
T& getMax(T& a, T& b) {
if(a > b)
return a;
else
return b;
}
template <>
Student& getMax<Student>(Student& s1, Student& s2) {
if(s1.getScore() > s2.getScore())
return s1;
else
return s2;
}
int main() {
int a = 10;
int b = 20;
int& max = getMax(a,b);
cout << "max = " << max << endl;
Student s1;
s1.setScore(78);
cout << "s1 score = " << s1.getScore() << endl;
Student s2;
s2.setScore(50);
cout << "s2 score = " << s2.getScore() << endl;
// 呼叫模板特製化
Student& ref = getMax(s1, s2);
cout << "score = " << ref.getScore()<< endl;
return 0;
}
max = 20
s1 score = 78
s2 score = 50
score = 78