std :: cout的字符串不起作用

Question

I have a class State that has a string data type called moveType . In the implementation of my code, I am calling a setter void setMoveType(string _moveType); and it's implemented with just moveType = _moveType;

When I call my getter string getMoveType() const; on an instance of State and output it to cout, nothing is displayed.

I am couting upon entering the getMoveType() function. The parameter indeed has the correct value, but it appears that it's not getting set at all.

Does anyone have any idea? I feel this is something simple/trivial in c++ that I'm just completely forgetting.

string  State::getMoveType() const {
    return moveType;
}

void State::setMoveType(string move_type)  {
    cout << "In setMoveType and param = " << move_type << endl;
    moveType = move_type;
}

std::cout << vec_possibleSuccessors[i].getMoveType() << endl; // within loop;

vector<State> vec_possibleSuccessors;

    if (_minState.canMoveUp()) {
        up = _minState.moveUp();
        up.setMoveType("UP");
        up.setF(f(up));
        vec_possibleSuccessors.push_back(up);
    }

In the above code, _minState and up are instances of State . Also, I have made sure that my copy constructor and assignment operator have been modified to include moveType assignments.

Answer 1

没有足够的代码可以肯定地知道，但我有一个猜测：要么你实际上分配给“set”函数中的阴影变量而根本没有设置class属性，或者你的State对象实际上已经被破坏了字符串变为空（因为在使用销毁的内存时，为空是一种可能的选项）。

Answer 2

I'm not sure on this either, but you appear to be storing this State in a vector. Could you post the code to how you set elements in the vector? Its important to note that you can't update an element in a vector once its inserted (unless you store a pointer to the element). Also depending upon how you call set, there may be problems.

Answer 3

Well not an answer but a short example that works the way you seem to intend this to work:

#include <string>

class State
{
  private:
    std::string m_moveType;

  public:
    State() : m_moveType( "unknown" ) {}

   std::string getMoveType() const { return m_moveType; }
   void setMoveType( const std::string& moveType ) { m_moveType = moveType; }
};

In your main function or were else you need a vector of States you could write this:

#include <iostream>
#include <vector>
#include "State.h"

int main()
{
  std::vector< State > states;
  for( int i=0; i<10; ++i )
  {
    State newState;
    newState.setMoveType( "state" );
    states.push_back( newState );
  }

  // do whatever you need to do....
  std::vector< State >::iterator it;
  std::vector< State >::iterator end = states.end();
  for( it=states.begin(); it != end; ++it )
    std::cout << (*it).getMoveType() << std::endl;

  return 0;
}

A few remarks:

• passing parameters by value like setMoveType( string s ) is not
  adviseable, pass const references instead. Passing by value incurrs a full copy of the passed object
• be careful with includes and namespaces, in doubt take the extra time to type std::... if you intend to use a feature defined in namespace std, and never type using namespace std in a header file.
• initialize private members to a sensible default and do it in the class initializer list