嵌套对象的copy-constructor

代码：
#include <iostream.h>
#include <string.h>
#include <fstream.h>
ofstream out("autoclearcase/" target="_blank" >cc.out");
class inside_withCC {
        static int inside_withCC_object_count;
public:
    inside_withCC(){
    out << "inside_withCC constructions function is called" << endl;
    inside_withCC_object_count++;
    out << "inside_withCC(): inside_withCC_object_count = " << inside_withCC_object_count << endl;
    }
    inside_withCC(const inside_withCC&) {
        out << "inside_withCC copy-constructions function is called" << endl;
        inside_withCC_object_count++;
    out << "inside_withCC(const withCC&): inside_withCC_object_count = " << inside_withCC_object_count << endl;

    }
};

int inside_withCC::inside_withCC_object_count = 0;

class withCC {
    static int withCC_object_count;
    inside_withCC IWITHCC;
public:
    withCC(){
    out << "withCC constructions function is called" << endl;
    withCC_object_count++;
    out << "withCC(): withCC_object_count = " << withCC_object_count << endl;
    }
    withCC(const withCC&) {
        out << "withCC copy-constructions function is called" << endl;
        withCC_object_count++;
    out << "withCC(const withCC&): withCC_object_count = " << withCC_object_count << endl;

    }
};

int withCC::withCC_object_count = 0;

class woCC {
    enum { bsz = 30 };
    char buf[bsz];
    static int woCC_object_count;
public:
    woCC(const char* msg = 0) {
        memset(buf, 0, bsz);
        if(msg) strncpy(buf, msg, bsz);
        out << "woCC construction function is  called" << endl;
        woCC_object_count++;
        out << "woCC(): woCC_object_count: " << woCC_object_count << endl;
    }

    void print(const char* msg = 0) const {
        if(msg) out << msg << ": ";
        out << buf << endl;
    }
};
int woCC::woCC_object_count = 0;

class composite {
    withCC WITHCC;
    woCC WOCC;
    static int composite_object_count;
public:
    composite():WOCC("composite()") {
    out << "composite constructor function is called" << endl;
    composite_object_count++;
    out << "composite(): composite_object_count: " << composite_object_count << endl;
    }
    composite(const composite& cmp)
    {
        out << "composite copy-constructor function is called" << endl;
        composite_object_count++;
        out << "composite(composite&): composite_object_count:" << composite_object_count << endl;

    }

    void print(const char* msg = 0) {
        WOCC.print(msg);
    }
};


int composite::composite_object_count = 0;

int main(int argc, char* argv[])
{
    composite c;
    c.print("contents of c");
    out << "calling composite copy-constructor"
        << endl;
    composite c2 = c;
    c2.print("contents of c2");
    return 0;
}

autocc.out文件为：
inside_withCC constructions function is called
inside_withCC(): inside_withCC_object_count = 1
withCC constructions function is called
withCC(): withCC_object_count = 1
woCC construction function is  called
woCC(): woCC_object_count: 1
composite constructor function is called
composite(): composite_object_count: 1
contents of c: composite()
calling composite copy-constructor
inside_withCC constructions function is called
inside_withCC(): inside_withCC_object_count = 2
withCC constructions function is called
withCC(): withCC_object_count = 2
woCC construction function is  called
woCC(): woCC_object_count: 2
composite copy-constructor function is called
composite(composite&): composite_object_count:2
contents of c2:

可见：如果母对象中显式的定义了X(X&)，则子对象初始化时调用构造函数初始化。

现在将程序改为：
#include <iostream.h>
#include <string.h>
#include <fstream.h>
ofstream out("autocc.out");
class inside_withCC {
        static int inside_withCC_object_count;
public:
    inside_withCC(){
    out << "inside_withCC constructions function is called" << endl;
    inside_withCC_object_count++;
    out << "inside_withCC(): inside_withCC_object_count = " << inside_withCC_object_count << endl;
    }
    inside_withCC(const inside_withCC&) {
        out << "inside_withCC copy-constructions function is called" << endl;
        inside_withCC_object_count++;
    out << "inside_withCC(const withCC&): inside_withCC_object_count = " << inside_withCC_object_count << endl;

    }
};

int inside_withCC::inside_withCC_object_count = 0;

class withCC {
    static int withCC_object_count;
    inside_withCC IWITHCC;
public:
    withCC(){
    out << "withCC constructions function is called" << endl;
    withCC_object_count++;
    out << "withCC(): withCC_object_count = " << withCC_object_count << endl;
    }
    withCC(const withCC&) {
        out << "withCC copy-constructions function is called" << endl;
        withCC_object_count++;
    out << "withCC(const withCC&): withCC_object_count = " << withCC_object_count << endl;

    }
};

int withCC::withCC_object_count = 0;

class woCC {
    enum { bsz = 30 };
    char buf[bsz];
    static int woCC_object_count;
public:
    woCC(const char* msg = 0) {
        memset(buf, 0, bsz);
        if(msg) strncpy(buf, msg, bsz);
        out << "woCC construction function is  called" << endl;
        woCC_object_count++;
        out << "woCC(): woCC_object_count: " << woCC_object_count << endl;
    }

    void print(const char* msg = 0) const {
        if(msg) out << msg << ": ";
        out << buf << endl;
    }
};
int woCC::woCC_object_count = 0;

class composite {
    withCC WITHCC;
    woCC WOCC;
    static int composite_object_count;
public:
    composite():WOCC("composite()") {
    out << "composite constructor function is called" << endl;
    composite_object_count++;
    out << "composite(): composite_object_count: " << composite_object_count << endl;
    }
/*    composite(const composite& cmp)
    {
        out << "composite copy-constructor function is called" << endl;
        composite_object_count++;
        out << "composite(composite&): composite_object_count:" << composite_object_count << endl;

    }
*/
    void print(const char* msg = 0) {
        WOCC.print(msg);
    }
};


int composite::composite_object_count = 0;

int main(int argc, char* argv[])
{
    composite c;
    c.print("contents of c");
    out << "calling composite copy-constructor"
        << endl;
    composite c2 = c;
    c2.print("contents of c2");
    return 0;
}

autocc.out的内容为：
inside_withCC constructions function is called
inside_withCC(): inside_withCC_object_count = 1
withCC constructions function is called
withCC(): withCC_object_count = 1
woCC construction function is  called
woCC(): woCC_object_count: 1
composite constructor function is called
composite(): composite_object_count: 1
contents of c: composite()
calling composite copy-constructor
inside_withCC constructions function is called
inside_withCC(): inside_withCC_object_count = 2
withCC copy-constructions function is called
withCC(const withCC&): withCC_object_count = 2
contents of c2: composite()

可见，如果母对象没有定义X(X&),则母对象采用位拷贝，不掉用任何构造函数，子对象中如果有现式的定义X(X&)的，则调用之，否则采用位拷贝。

原文转自：http://www.ltesting.net