I'm not the creator of notes, I'm just a porter of notes ~
1. The constructor can be overloaded, or it can be a
parameterless constructor
string s that
matches string with default parameters ; a parameter (const char *) constructor
string s ("hello") that matches string
2, the default constructor (no parameter constructor)
1) If no constructor is defined in the class, the compiler will provide a default (no parameter) constructor for the class:
-"Do not do for basic type member variables Initialization-
"For member variables of class type (member sub-objects), it will automatically call the parameterless constructor of the corresponding class to initialize
2) If you define a constructor yourself, regardless of whether there are parameters, then the compiler will no longer provide the default parameterless constructor.
3, type conversion constructor (single-parameter constructor) // type conversion of the constructor
class class name {
// Can convert source type variables to current class type objects.
Class name (source type) {...}
};
-----------------------------------
class class name {
// Add "explicit" keyword modification, you can Mandatory that this type
// conversion must be done
explicitly . Explicit class name (source type) {...}
};
4. The copy constructor (copy constructor) I think this part is quite difficult to understand.
1) Use an existing object as the construction parameter of similar objects. When creating a new copy object, the copy constructor will be called.
class class name {
class name (const class name &) {// copy structure
...
}
};
------------
eg:
class A {...};
A a1 (.. .);
A a2 (a1); // Matching A's copy constructor
2) If a class does not define its own copy constructor, then the compiler will provide a default copy constructor for the class:
-> For member variables of the basic type, copy by byte
->> For members of the class type Variable (member sub-object), will automatically call the copy constructor of the corresponding class to initialize
Note: It is generally not necessary to define the copy constructor function by yourself, because the compiler provides it by default is already very easy to use.
class A1 {}; // No parameter by default, default copy
class A2 {// default copy
A (void) {}
};
class A3 {// default copy
A (int) {}
};
class A4 { // There is no default structure
A (const A &) {}
};
3) The timing of copy constructor call-
"Use an existing object as the construction parameter of the same kind of object-
" Pass parameters to the function in the form of object-
"Return the object from the function (it may be optimized by the compiler)
