类模板也可以半特化 partial specialization
意味着在模板特化的某些方法至少还有一个方法
器模板参数是开放的
//: C05:PartialOrder2.cpp
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// Reveals partial ordering of class templates.
#include <iostream>
using namespace std;
template<class T, class U> class C {
public:
void f() { cout << "Primary Template\n"; }
};
template<class U> class C<int, U> {
public:
void f() { cout << "T == int\n"; }
};
template<class T> class C<T, double> {
public:
void f() { cout << "U == double\n"; }
};
template<class T, class U> class C<T*, U> {
public:
void f() { cout << "T* used\n"; }
};
template<class T, class U> class C<T, U*> {
public:
void f() { cout << "U* used\n"; }
};
template<class T, class U> class C<T*, U*> {
public:
void f() { cout << "T* and U* used\n"; }
};
template<class T> class C<T, T> {
public:
void f() { cout << "T == U\n"; }
};
int main() {
C<float, int>().f(); // 1: Primary template
C<int, float>().f(); // 2: T == int
C<float, double>().f(); // 3: U == double
C<float, float>().f(); // 4: T == U
C<float*, float>().f(); // 5: T* used [T is float]
C<float, float*>().f(); // 6: U* used [U is float]
C<float*, int*>().f(); // 7: T* and U* used [float,int]
// The following are ambiguous:
// 8: C<int, int>().f();
// 9: C<double, double>().f();
// 10: C<float*, float*>().f();
// 11: C<int, int*>().f();
// 12: C<int*, int*>().f();
getchar();
} ///:~
输出
Primary Template
T == int
U == double
T == U
T* used
U* used
T* and U* used
可以根据模板参数是否是指针类型
或者它们是否和特化参数类型相同来部分指定模板参数
当用T*作为模板参数来进行特化时
T本身不是最高级的被传递的指针类型