c++ 模板 指针类型偏特化

一步步来,先简单点.
目标:我们要实现一个模板类,例化后,可以通过get_val获取到值,通过get_ptr获取到指针.具体什么意思结合例子来看看吧.
例子:

struct A{     int data;     A(int _data = 0):data(_data){} }; template <typename T>  class heap_node{  public:  	 typedef T  val_type; 	 typedef T* ptr_type; 	 typedef T& ref_type; 	 ptr_type data; 	 ref_type get_val() { return *data; } 	 ptr_type get_ptr() { return data; } 	 heap_node(ptr_type d) :data(d){ 		 printf("<T> (T*)n"); 	 } 	 heap_node(ref_type d) :data(&d){ 		 printf("<T> (T)n"); 	 }  };   int main() { 	 A a(10); 	 printf("ptr=%pn",&a); 	 heap_node<A> p0(a); 	 printf("ptr=%p val=%dn", p0.get_ptr(),p0.get_val().data); 	 heap_node<A> p1(&a); 	 printf("ptr=%p val=%dn", p1.get_ptr(), p1.get_val().data); 	/* 	 heap_node<A*> p2(a); 	 printf("ptr=%p val=%dn", p2.get_ptr(), p2.get_val().data); 	 heap_node<A*> p3(&a); 	 printf("ptr=%p val=%dn", p3.get_ptr(), p3.get_val().data); 	*/      char ch = getchar(); }   

(不要在类里直接保存值类型的数据,可以用指针或者引用都可以)
发现heap_node<A> p2(a)或者heap_node<A> p3(&a)的时候,无法正常表达我们原来的意识,此时的val_type就变成指针类型,怎么解决呢.需要对<T*>特殊处理一下.

struct A{     int data;     A(int _data = 0):data(_data){} }; template <typename T>  class heap_node{  public:  	 typedef T  val_type; 	 typedef T* ptr_type; 	 typedef T& ref_type; 	 ptr_type data; 	 ref_type get_val() { return *data; } 	 ptr_type get_ptr() { return data; } 	 heap_node(ptr_type d) :data(d){ 		 printf("<T> (T*)n"); 	 } 	 heap_node(ref_type d) :data(&d){ 		 printf("<T> (T)n"); 	 }  }; //<T*>偏特化 template <typename T>  class heap_node<T*>{  public:  	 typedef T  val_type; 	 typedef T* ptr_type; 	 typedef T& ref_type; 	 ptr_type data; 	 ref_type get_val() { return *data; } 	 ptr_type get_ptr() { return data; } 	 heap_node(ptr_type d) :data(d){ 		 printf("<T*> (T*)n"); 	 } 	 heap_node(ref_type d) :data(&d){ 		 printf("<T*> (T)n"); 	 }  };  int main() { 	 A a(10); 	 printf("ptr=%pn",&a); 	 heap_node<A> p0(a); 	 printf("ptr=%p val=%dn", p0.get_ptr(),p0.get_val().data); 	 heap_node<A> p1(&a); 	 printf("ptr=%p val=%dn", p1.get_ptr(), p1.get_val().data); 	 	 heap_node<A*> p2(a); 	 printf("ptr=%p val=%dn", p2.get_ptr(), p2.get_val().data); 	 heap_node<A*> p3(&a); 	 printf("ptr=%p val=%dn", p3.get_ptr(), p3.get_val().data); 	      char ch = getchar(); } 

可能还有const修饰T,或者实例化T为原始数据类型......,都可能出现类似的问题,可以用偏特化解决.这里就不一一列举出来哈.
我们可以发现,特例化的<T*>模板与原模板代码上几乎一样的,是不是可以优化一下呢.
直接上代码:

struct A{     int data;     A(int _data = 0):data(_data){} };  template <class T>  struct heap_node_type{ 	 typedef T  val_type; 	 typedef T* ptr_type; 	 typedef T& ref_type;  };   template <class T>  struct heap_node_type<T*>{ 	 typedef T  val_type; 	 typedef T* ptr_type; 	 typedef T& ref_type;  };   template <class T>  class heap_node :heap_node_type<T>{  public: 	 ptr_type data; 	 ref_type get_val() { return *data; } 	 ptr_type get_ptr() { return data; } 	 heap_node(ptr_type d) :data(d){ 		 printf("<T> (T*)n"); 	 } 	 heap_node(ref_type d) :data(&d){ 		 printf("<T> (T)n"); 	 }  };    int main() { 	 A a(10); 	 printf("ptr=%pn",&a); 	 heap_node<A> p0(a); 	 printf("ptr=%p val=%dn", p0.get_ptr(),p0.get_val().data); 	 heap_node<A> p1(&a); 	 printf("ptr=%p val=%dn", p1.get_ptr(), p1.get_val().data);  	 heap_node<A*> p2(a); 	 printf("ptr=%p val=%dn", p2.get_ptr(), p2.get_val().data); 	 heap_node<A*> p3(&a); 	 printf("ptr=%p val=%dn", p3.get_ptr(), p3.get_val().data);  	 int b = 100; 	 printf("==========int====nptr=%pn", &b); 	 heap_node<int> p4(b); 	 printf("ptr=%p val=%dn", p4.get_ptr(), p4.get_val()); 	 heap_node<int> p5(&b); 	 printf("ptr=%p val=%dn", p5.get_ptr(), p5.get_val());  	 heap_node<int*> p6(b); 	 printf("ptr=%p val=%dn", p6.get_ptr(), p6.get_val()); 	 heap_node<int*> p7(&b); 	 printf("ptr=%p val=%dn", p7.get_ptr(), p7.get_val());  	 string str = "string"; 	 printf("==========str====nptr=%p %sn", &str,str); 	 heap_node<string> s4(str); 	 printf("ptr=%p val=%sn", s4.get_ptr(), s4.get_val()); 	 heap_node<string> s5(&str); 	 printf("ptr=%p val=%sn", s5.get_ptr(), s5.get_val());  	 heap_node<string*> s6(str); 	 printf("ptr=%p val=%sn", s6.get_ptr(), s6.get_val()); 	 heap_node<string*> s7(&str); 	 printf("ptr=%p val=%sn", s7.get_ptr(), s7.get_val());  	 const int c = 123; 	 printf("==========const int====nptr=%pn", &c); 	 heap_node<const int> c4(c); 	 printf("ptr=%p val=%dn", c4.get_ptr(), c4.get_val()); 	 heap_node<const int> c5(&c); 	 printf("ptr=%p val=%dn", c5.get_ptr(), c5.get_val());  	 heap_node<const int*> c6(c); 	 printf("ptr=%p val=%dn", c6.get_ptr(), c6.get_val()); 	 heap_node<const int*> c7(&c); 	 printf("ptr=%p val=%dn", c7.get_ptr(), c7.get_val());      char ch = getchar(); }