C ++中此星号(*)的含义是什么? -指向成员的指针 [英] What is the meaning of this star (*) symbol in C++? -- Pointer to member

问题描述

在我的项目中，MyClass.h文件中有几行

In my project, there are a few lines in a MyClass.h file

class MyClass{
public:
....

#ifndef __MAKECINT__
  std::vector<Status_e(MyClass::*)(TupleInfo & info)> m_processObjects; //!
#endif
....
}
//The Status_e is an enum type
//The TupleInfo is a struct

我不明白上面的代码片段中此*的用法.在MyClass.cxx文件中，m_processObjects用作:

I can't understand what the usage of this * in above code snippet. And in the MyClass.cxx file, the m_processObjects used as this:

for (unsigned int f = 0; f < m_processObjects.size(); ++f) {
    status = (this->*m_processObjects[f])( m_tuples[i] );
    if ( status == FAILURE ) {
      return EL::StatusCode::FAILURE;
    }
....
}
....

我从未听说过像this->*blabla这样的用法，但是此代码段有效.那是什么意思?

I have never heard about the usage like this->*blabla, but this code snippet works. So what it means?

推荐答案

::*表示与周围的代码一起，它实际上是指向成员函数的指针.

With the surrounding code it's actually a Pointer to member function.

Status_e(MyClass::*)(TupleInfo & info)

是class MyClass的成员函数，返回Status_e，并具有一个参数TupleInfo&. (参数名称info在这里没有用，但显然被编译器默默忽略了.)

is a member function of class MyClass, returning Status_e, and having one paramter TupleInfo&. (The argument name info is useless here but obviously silently ignored by the compiler.)

OP问题中的另一个代码片段显示了如何调用它:

The other snippet in OP's question shows how to call it:

status = (this->*m_processObjects[f])(m_tuples[i]);

存储方法指针如下所示:

Storing a method pointer would look like this:

std::vector<Status_e(MyClass::*)(TupleInfo & info)> m_processObjects;

...

m_processObjects.push_back(&MyClass::aMethod);

当然，MyClass::aMethod的签名必须匹配.

Of course, the signature of MyClass::aMethod must match.

一个简单的示例来演示它:

A simplified sample to demonstrate it:

#include <iostream>
#include <vector>

class Test {

  private:
    std::vector<int(Test::*)(const char*)> _tblTestFuncs;
  public:
    Test()
    {
       _tblTestFuncs.push_back(&Test::func1);
       _tblTestFuncs.push_back(&Test::func2);
       _tblTestFuncs.push_back(&Test::func3);
    }

    int func1(const char *caller) { std::cout << "Test::func1 called from '"<< caller << "': "; return 1; }
    int func2(const char *caller) { std::cout << "Test::func2 called from '"<< caller << "': "; return 2; }
    int func3(const char *caller) { std::cout << "Test::func3 called from '"<< caller << "': "; return 3; }

    void call()
    {
      for (size_t i = 0, n = _tblTestFuncs.size(); i < n; ++i) {
        int result = (this->*_tblTestFuncs[i])("Test::call()");
        std::cout << "Return: " << result << '\n';
      }
    }
};

int main()
{
  Test test;
  // test method vector in main()
  std::vector<int(Test::*)(const char*)> tblTestFuncs;
  tblTestFuncs.push_back(&Test::func1);
  tblTestFuncs.push_back(&Test::func2);
  tblTestFuncs.push_back(&Test::func3);
  for (size_t i = 0, n = tblTestFuncs.size(); i < n; ++i) {
    int result = (test.*tblTestFuncs[i])("main()");
    std::cout << "Return: " << result << '\n';
  }
  // test method vector in Test
  test.call();
  // done
  return 0;
}

输出:

Test::func1 called from 'main()': Return: 1
Test::func2 called from 'main()': Return: 2
Test::func3 called from 'main()': Return: 3
Test::func1 called from 'Test::call()': Return: 1
Test::func2 called from 'Test::call()': Return: 2
Test::func3 called from 'Test::call()': Return: 3

coliru.com上的实时演示

这篇关于C ++中此星号(*)的含义是什么? -指向成员的指针的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！