- 首页 > it技术 > >
《More Effective C++》技术篇——限制某个class所能产生的对象数量
- 【《More Effective C++》技术篇——限制某个class所能产生的对象数量】如下例，只要继承Counted template就可以限制class所能产生的对象数量，超过了设置的maxObjects就会抛出异常。
#include
#include template
class Counted {
public:
class TooManyObjects{};
//这是可能被抛出的exceptions。
static int objectCount() { return numObjects;
}protected:
Counted();
Counted(const Counted& rhs);
~Counted() { --numObjects;
}private:
static int numObjects;
static const size_t maxObjects;
void init();
//用以避免ctor码重复出现。
};
template
Counted::Counted()
{ init();
}template
Counted::Counted(const Counted& rhs)
{ init();
}template
void Counted::init()
{
if (numObjects >= maxObjects)
{
throw TooManyObjects();
}++numObjects;
}template
int Counted::numObjects = 0;
class Printer: private Counted {
public:
// pseudo-constructors
static Printer* makePrinter() { return new Printer();
}
static Printer* makePrinter(const Printer& rhs) { return new Printer(rhs);
}
~Printer() {}using Counted::objectCount;
using Counted::TooManyObjects;
private:
Printer() {}
Printer(const Printer& rhs) {}
};
template
const size_t Counted::maxObjects = 5;
int main()
{
auto p1 = Printer::makePrinter();
auto p2 = Printer::makePrinter();
auto p3 = Printer::makePrinter();
std::cout << "now Printer num = " << p1->objectCount() << std::endl;
auto p4 = Printer::makePrinter(*p1);
auto p5 = Printer::makePrinter(*p2);
std::cout << "now Printer num = " << p1->objectCount() << std::endl;
//auto p6 = Printer::makePrinter(*p3);
//抛出TooManyObjects的异常。
}
推荐阅读
