"Go" How to call another constructor in a constructor in C + +

In C + +, a class's constructor cannot directly invoke another constructor, such as:

1 #ifndef _a_h_2     #define_a_h_3#include <stdio.h>4#include <New>5     classA6     {7      Public:8 A ()9             {Tenprintf"In A::(). m_x=%d\n", m_x); OneA0); Aprintf"Out A::(). m_x=%d\n", m_x); -  -             } the  -  -Aintx) -             { +printf"In A::(int x). x=%d\n", x); -m_x=x; +             } A  at     Private: -             intm_x; -};

Here the 11th line calls a (0); just constructs a temporary object, and does not call a (int x) to initialize itself. The result of the operation is:

[Email protected] utcov]#./utest.  out In A::(). m_x=4268020inA::(int x). x=0outA::(). m_x=4268020

As you can see, although a (0) is called, m_x still does not change, which is 4268020.
The correct approach is to use placement NEW:

1     //A.h2 #ifndef _a_h_3     #define_a_h_4#include <stdio.h>5#include <New>6     classA7     {8      Public:9 A ()Ten             { Oneprintf"In A::(). m_x=%d\n", m_x); A                     New( ThisA0); -printf"Out A::(). m_x=%d\n", m_x); -  the             } -  -  -Aintx) +             { -printf"In A::(int x). x=%d\n", x); +m_x=x; A             } at  -  -     Private: -             intm_x; -     }; -  in     #endif

The 11th line shall be: New (This) A (0); That is, the constructor a (int x) is called with the current object to construct a "new" object. The result of the operation is:

    [Email protected] utcov]#./utest.  out In     A::(). m_x=4268020in    A::(int x). x=0out    A::(). m_x=0

As you can see, the current object is indeed changed.

"Go" How to call another constructor in a constructor in C + +