Problem about usage of "this" keyword in C++

class Monitor
{
private:
    int 开发者_如何学编程rate;

    Monitor(int rate)
    {
        this.rate = rate;
    }
}

This is my code. I try to set the private member "rate" with local member that passes through constructor "rate". But I could use it like that In C#.

The error is:

expression must have class type

this is a pointer, as others have said, but it's much better and more correct to use the base initializer list:

class Monitor
{
   int rate;
public:
   Monitor(int rate) : rate(rate) { }
};

That way, Monitor::rate gets initialized to the right value, rather than first default-initalized and then assigned. For more general member objects this may in fact be the only legitimate way to initialize them.

class Monitor
{
private:
    int rate;

    Monitor(int rate)
    {
        this->rate = rate;
    }
}

this needs to be treated like a pointer. Hence the ->

When you refer to this, you're accessing a pointer to the object. What you want to do is:

Monitor(int rate)
{
    this->rate = rate;
}

this keyword represent a pointer to the current object. You have to write:

this->rate = rate;

Dot notation is used if you have a instance of the class.

Monitor(int r)
    {
        rate = r;
    }

Or better still:

Monitor(int r): rate(r)
    {}

this->rate = rate. Pointers use the -> operator in C++.

Since this is a pointer to self, then you must use it as such. This fixes your problem :

class Monitor
{
private:
    int rate;

    Monitor(int rate)
    {
        this->rate = rate; // this is a pointer
    }
};

Though it is perfectly legal C++ code, one should not use same names for argument(s) and member(s) of a class. Better implementation would be:

    class Monitor
    {
    private:    
         int Rate;     // Or m_nRate
    public:
          Monitor(int rate /* OR nRate */) : Rate(rate) /* m_nRate(nRate);*/

          // OR
          Monitor(int rate /* OR nRate */)
          {
              Rate = rate; // this->Rate = rate;     // this->m_nRate = nRate;
          }
      };