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【cmu15445c++入门】(5)c++中的模板类

news 来源：原创 2024/5/14 6:38:25

一、template模板类

除了模板方法【cmu15445c++入门】(4)c++中的模板方法

模板也可以用来实现类

二、代码

/*** @file templated_classes.cpp* @author Abigale Kim (abigalek)* @brief Tutorial code for templated classes.*/// Includes std::cout (printing).
#include <iostream>// Templates can be also used to implement classes. For instance, here is a
// basic templated class that stores one element of a templated type and
// prints it when the print function is called.//模板也可以用来实现类
template<typename T>
class Foo {public:Foo(T var) : var_(var) {}void print() {std::cout << var_ << std::endl;}private:T var_;
};// You can also pass in multiple type names via templates into classes. 
// For instance, here's another basic templated class that stores two
// elements of a templated type and prints them when the print function
// is called.
// 模板类可以支持多个类型
template<typename T, typename U> 
class Foo2 {public:Foo2(T var1, U var2) : var1_(var1), var2_(var2) {}void print() {std::cout << var1_ << " and " << var2_ << std::endl;}private:T var1_;U var2_;
};// It is also possible to create specialized templated classes, that do
// different things for different types. Take the following contrived example,
// which instantiates a class with a print function that outputs the value of
// the variable stored if it's any other type but float. If the class is 
// instantiated with a float type, it prints out hello float and the variable
// the class stores in its var_ field.//模板类也可以针对特定的类型做特定的处理
template<typename T>
class FooSpecial {public:FooSpecial(T var) : var_(var) {}void print() {std::cout << var_ << std::endl;}private:T var_;
};// Specialized templated class, specialized on the float type.
template<>
class FooSpecial<float> {public:FooSpecial(float var) : var_(var) {}void print() {std::cout << "hello float! " << var_ << std::endl;}private:float var_;
};// Template parameters don't have to be types. They can also be values!
template<int T>
class Bar {public: Bar() {}void print_int() {std::cout << "print int: " << T << std::endl;}
};int main() {// First, let us construct an object from a templated class. The Foo// class template is instantiated with an int template argument. This// would make a's type class Foo<int> instead of Foo. a's print // function works as expected.Foo<int> a(3);std::cout << "Calling print on Foo<int> a(3): ";a.print();// It is also possible for a templated class to interpret the type// of its arguments. Once again, if you're a beginner, think twice// before doing this if you are unsure of the types you are // instantiating your class with.Foo b(3.4f);std::cout << "Calling print on Foo b(3.4f): ";b.print();// Second, we construct an object from a templated class with multiple// type arguments.Foo2<int, float> c(3, 3.2f);std::cout << "Calling print on Foo2<int, float> c(3, 3.2f): ";c.print();// Let's see what happens when we instantiate FooSpecial both with// and without the float type argument. As expected when we call// print from d, it prints the variable and not "hello float".// When we call print from e, which is an instance of the// instantiated FooSpecial<float> class, it prints hello float!FooSpecial<int> d(5);std::cout << "Calling print on FooSpecial<int> d(5): ";d.print();FooSpecial<float> e(4.5);std::cout << "Calling print on FooSpecial<float> e(4.5): ";e.print();// Lastly, let's see what happens when we construct an object from a// templated class with non-type arguments.Bar<150> f;std::cout << "Calling print_int on Bar<150> f: ";f.print_int();// Once again, these are contrived examples, but it is still important// to understand them you'll be seeing code similar to this in the Bustub// codebase, so it's good to understand templated classes in these contexts!// 最后，需要注意的是，以上大多数都是人为的示例，但还是要理解下，可能在海量的代码中看到。return 0;
}