这个star(*)符号在C++中的含义是什么？ - 指向会员的指针

Question

在我的项目中,MyClass.h文件中有几行

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*在上面的代码片段中无法理解这个用法.在MyClass.cxx文件中,m_processObjects用作:

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;
    }
....
}
....

我从来没有听说过这样的用法this->*blabla,但这段代码片段有效.那意味着什么？

Answer 1

::*表示成员的指针.

使用周围的代码,它实际上是指向成员函数的指针.

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

是一个成员函数class MyClass,返回Status_e,并有一个参数TupleInfo&.(参数名称info在这里没用,但编译器显然会默默忽略.)

OP问题中的另一个片段显示了如何调用它:

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

存储方法指针看起来像这样:

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

...

m_processObjects.push_back(&MyClass::aMethod);

当然,签名MyClass::aMethod必须匹配.

一个简化的示例来演示它:

#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

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