关于 Constructor&Destructor

[kwib799]

请问Constructor&Destructor是不是必须一一对应的，也就是说没调用一次CON就得调用一次DES，如果是的话，下面的程序哪位给解释一下。为什么只调用了一次CON后却调用了3次DES。

#include <fstream>
#include <string>
using namespace std;
ofstream out("HowMany.out");

class HowMany {
static int objectCount;
public:
HowMany() { objectCount++;out<<"Constructor called!"<<endl;}
static void print(const string& msg = "") {
if(msg.size() != 0) out << msg << ": ";
out << "objectCount = "
<< objectCount << endl;
}
~HowMany() {
objectCount--;
print("~HowMany()");
}
};

int HowMany::objectCount = 0;

// Pass and return BY VALUE:
HowMany f(HowMany x) {
x.print("x argument inside f()");
return x;
}

int main() {
HowMany h;
HowMany::print("after construction of h");
HowMany h2 = f(h);
HowMany::print("after call to f()");
} ///:~

[abitz]

int main() {
HowMany h; // default ctor called
HowMany::print("after construction of h");
HowMany h2 = f(h); // f(h):copy ctor called, when returning, dtor called;
// h2 = f(h); default operator = called;
HowMany::print("after call to f()");
} // at the end dtor of h and h2 called
// total dtor called: 3 times

[abitz]

改成这样就好了：
#include <fstream>
#include <string>
using namespace std;
ofstream out("HowMany.out");

class HowMany {
static int objectCount;
public:
HowMany() { objectCount++;out<<"Constructor called!"<<endl;}
HowMany(const HowMany& x) {objectCount++; out<<"Copy Ctor called!"<<endl;}
HowMany& operator=(const HowMany& x)
{objectCount++;out<<"operator = called!"<<endl;
return *this;}
static void print(const string& msg = "")
{
if(msg.size() != 0) out << msg << ": ";
out << "objectCount = "
<< objectCount << endl;
}
~HowMany() {
objectCount--;
print("~HowMany()");
}
};

int HowMany::objectCount = 0;

// Pass and return BY VALUE:
HowMany f(HowMany x) {
x.print("x argument inside f()");
return x;
}

int main() {
HowMany h;
HowMany::print("after construction of h");
HowMany h2 = f(h); // h2 = f(h)这里没有调用operator=,而是copy ctor.
// 不解
HowMany::print("after call to f()");
} ///:~

[abitz]

运行结果：
Constructor called!
after construction of h: objectCount = 1
Copy Ctor called! // f(h),pass by value,利用copy ctor产生临时对象
x argument inside f(): objectCount = 2
Copy Ctor called! // h2 = f(h);不是operator=，而是copy ctor;
~HowMany(): objectCount = 2 // 临时对象析构
after call to f(): objectCount = 2
~HowMany(): objectCount = 1
~HowMany(): objectCount = 0

[kwib799]

您在这里加进一个 OPERATOR OVERLOADING 是什么意思？

[abitz]

我以为能调用它那。
不过结果不是这样。
为什么哪？

[kahn]

运算符重载，自定义的某个运算符

[kwib799]

会不会涉及到对象之间的操作调用CC和OPERATOR OVERLOADING时编译器会选择CC