一.sizeof模板化

#include <stddef.h> #include <iostream>template <typename T> class TypeSize {public:static size_t const value = sizeof(T); };int main() {std::cout << "TypeSize<int>::value = "<< TypeSize<int>::value << std::endl; }

二.獲取容器元素類型

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#include <vector> #include <list> #include <stack> #include <iostream> #include <typeinfo>template <typename T> class ElementT; // primary templatetemplate <typename T> class ElementT<std::vector<T> > { // partial specializationpublic:typedef T Type; };template <typename T> class ElementT<std::list<T> > { // partial specializationpublic:typedef T Type; };template <typename T> class ElementT<std::stack<T> > { // partial specializationpublic:typedef T Type; };template <typename T> void print_element_type (T const & c) {std::cout << "Container of "<< typeid(typename ElementT<T>::Type).name()<< " elements.\n"; }int main() {std::stack<bool> s;print_element_type(s); }

通過定義一個內部變量來簡化上述工作

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template <typename C> class ElementT { public: typedef typename C::value_type Type; };

標準庫都定義了這樣的類型

std::cout << "Container of "<< typeid( std::stack<bool>::value_type).name()<< " elements.\n";

通過此方法來簡化模板參數數量.

原先原型:

template <typename T, typename C> T sum_of_elements (C const& c);

利用上面的內部type簡化參數數量

template<typename C> typename ElementT<C>::Type sum_of_elements (C const& c);

三.確定一個對象是否是類類型

參考:http://www.cnblogs.com/mightofcode/archive/2013/04/07/3005849.html

#include <iostream>template<typename T> class IsClassT {typedef char _One;typedef struct{char a[2];}_Two;template<typename T>static _One isClass(int T::* p);template<typename T>static _Two isClass(...); public:enum { Yes = sizeof(isClass<T>(NULL))==sizeof(_One) };enum { No = !Yes };};class MyClass { }; struct MyStruct { }; union MyUnion { }; void myfunc() { } enum{e1}e; // check by passing type as template argument template <typename T> void check() { if (IsClassT<T>::Yes) { std::cout << " IsClassT " << std::endl; } else { std::cout << " !IsClassT " << std::endl; } } template <typename C> class ElementT { public: typedef typename C::value_type Type; }; // check by passing type as function call argument template <typename T> void checkT (T) { check<T>(); } int main() { std::cout << "int: "; check<int>(); std::cout << "MyClass: "; check<MyClass>(); std::cout << "MyStruct:"; MyStruct s; checkT(s); std::cout << "MyUnion: "; check<MyUnion>(); std::cout << "enum: "; checkT(e); std::cout << "myfunc():"; checkT(myfunc); }

四.引用和限定符

incr 函數將會使apply模板函數演繹成T&& arg,需要注意這點

#include <iostream> template <typename T> void apply (T& arg, void (*func)(T)) { func(arg); } void incr (int& a) { ++a; } void print (int a) { std::cout << a << std::endl; } int main() { int x=7; apply (x, print); //error//apply (x, incr); }

五.IfThenElse模板

用一個布爾值和特化技術來選擇類型

template<bool C, typename Ta, typename Tb> class IfThenElse; // partial specialization: true yields second argument template<typename Ta, typename Tb> class IfThenElse<true, Ta, Tb> { public: typedef Ta ResultT; }; // partial specialization: false yields third argument template<typename Ta, typename Tb> class IfThenElse<false, Ta, Tb> { public: typedef Tb ResultT; };

總結

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