什么是“操作符T *（void）”。和什么时候调用？ [英] what is "operator T*(void)" and when it is invoked?

问题描述

我有2个档案：

  / **** demo.cpp **** / 
＃ include< iostream.h> 
 #includegc.h
 
 class foo {}; 
 
 int main（）{
 gc< foo> x1; 
 cout<< x1; 
} 
 
 /*****gc.h*****/ 
 template< class T> class gc 
 {
 T * ptr; 
 public：
 operator T *（）{} 
}; 
  

如果我不写 code>然后我得到了很多编译器错误。

所以plz告诉我什么是 关于您的问题

解决方案

运算符类型（）是所谓的cast运算符。如果需要转换为类型，则使用该运算符函数进行转换。

在您的示例中，cout使用您的运算符T *（）转换为指针，然后通过ostream的（cout是类std :: ostream）运算符< 输出，它接受一个void *。

其他问题

要帮助您找出其他问题，请更改头文件名从 iostream.h 到 iostream 。标准C ++不知道 iostream.h 。这些文件被称为像C ++之前做的标准。此外，您使用的所有C头文件，例如 math.h，stdio.h 在C ++中仍然有效，但它们是所谓的向后兼容头文件。您应该包括例如 cmath 和 cstdio 。这将把所有不是C中的宏的名字放在命名空间std 中。而不是使用 cout ，您使用 std :: cout 。对于其他标识符也是如此。

I have 2 files:

/****demo.cpp****/
#include <iostream.h>
#include "gc.h"

class foo{};

int main(){
    gc<foo> x1;
    cout<<x1;
}

/*****gc.h*****/
template <class T> class gc 
{
    T* ptr;
public:
    operator T*(){}
};

If I don't write operator T*(){} then I get a lot of compiler errors.

So plz tell me what is operator T*(void) and when it is invoked?

解决方案

Regarding your Question

operator type () is a so-called cast operator. if there is a need for conversion to type, then that operator function is used to do the conversion.

in your example, cout uses your operator T* () to convert your x1 object using a user defined implicit conversion to a pointer, which is then output by ostream's (cout is of class std::ostream) operator<< which takes a void* .

Other Problems

To help you figure out other problems, change the header file name from iostream.h to iostream . Standard C++ does not know iostream.h . Those files were called like that before C++ was made a Standard. Also, all C headers you use, like math.h, stdio.h are still valid in C++, but they are so-called backward-compatibility header files. You should include for example cmath and cstdio instead. That will put all names that are not macros in C into the namespace std. Instead of using cout , you use std::cout . Likewise for other identifiers too.

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