C++ Passing `this` into method by reference

I have a class constructor that expects a reference to another class object to be passed in as an argument. I understand that references are preferable to pointers when no pointer arithmetic will be performed or when a null value will not exist.

This is the header declaration of the constructor:

class MixerLine {

private:
    MIXERLINE _mixerLine;

public:

    MixerLine(const MixerDevice& const parentMixer, DWORD destinationIndex); 

    ~MixerLine();
}

This is the code that calls the constructor (MixerDevice.cpp):

void MixerDevice::enumerateLines() {

    DWORD numLines = getDestinationCount();
    for(DWORD i=0;i<numLines;i++) {

        MixerLine mixerLine( this, i );
        // other code here removed
    }
}

Compilation of MixerDevice.cpp fails with this error:

Error 3 error C2664: 'MixerLine::MixerLine(const MixerDevice &,DWORD)' : cannot convert parameter 1 from 'MixerDevice *const ' to 'const MixerDevice &'

But I thought pointer values could be assigned to pointers, eg

Foo* foo = new Foo();
Foo& bar = foo;

---

this是一个指针，要得到一个引用，你必须解除引用（ *this ）它：

MixerLine mixerLine( *this, i );

---

You should dereference this , because this is a pointer, not a reference. To correct your code you should write

for(DWORD i=0;i<numLines;i++) {

    MixerLine mixerLine( *this, i ); // Ok, this dereferenced
    // other code here removed
}

Note: the second const at the constructor's parameter const MixerDevice& const parentMixer is completely useless.

---

To obtain a reference from a pointer you need to dereference the pointer, as it has already been mentioned. Additionally (maybe due to copying into the question?) the constructor should not compile:

const MixerDevice& const parentMixer

That is not a proper type, references cannot be const qualified, only the referred type can be, so the two (exactly equivalent) options are:

const MixerDevice& parentMixer
MixerDevice const& parentMixer

(Note that the const qualifying of MixerDevice can be done at either way, and it means exactly the same).

链接地址: http://www.djcxy.com/p/20784.html

上一篇: 通过引用或指针返回并检查null？

下一篇: C ++通过引用将`this`传入方法