[Valid C ++ Reading Notes] 005 _ clause 05 _ understand which functions C ++ writes and calls in silence

In fact, this is also mentioned in C ++'s basic introductory books, such as C ++ primer, but few people pay attention to it. The author puts forward this point, to remind us.

The content of this clause is as follows 【Code snippet 1After being processed by the compiler, the code you write is essentially 【Code snippet 2]:

Code snippet 1 (manually written by you ):

1 class  A{2 3 };

Code snippet 2 (generated by the compiler for you ):

1 class A{2 public:3     A() { ... }4     A(const A& rhs) { ... }5     ~A() { ... }6 7     A& operator =(const A& rhs) { ... }8 };

As can be seen from the above, the compiler adds a statement for us:

1. No parameter Constructor

2. copy constructors

3. destructor

4. Value assignment operator =

In these terms, the author explains another point, that is, whether to generate or not the assignment operator = generation rules? Let's look at two examples:

 1 #include <iostream> 2 using namespace std; 3  4 class A{ 5 }; 6  7 int main(){ 8     A a1; 9     A a2;10     a1 = a2;11     return 0;12 }

Result: The compilation is successful!

 1 #include <iostream> 2 using namespace std; 3  4 class A{ 5 public: 6     int value; 7     const int constValue; 8     A(int v):constValue(v){} 9 };10 11 int main(){12     A a1(10);13     A a2(20);14     a1 = a2;15     return 0;16 }

Result: The compilation fails, and the message "error: There is no '=' operator matching these operands" is displayed ".

This shows that:

When a constant is defined for a reference in a class, the compiler does not generate a '=' operator for it.