c++编程思想chapter12，简单的内存管理系统

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本文介绍了一个自定义内存管理实现的例子，通过重载new和delete操作符来管理内存池，展示了如何分配和释放内存块。

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#include <stddef.h>
#include <fstream.h>

ofstream out("framis.out");

class Framis
{
	char c[10];
	static unsigned char pool[];
	static unsigned char alloc_map[];
public:
	enum { PSIZE = 100 };
	Framis() { out << "framis()\n"; };
	~Framis() { out << "~framis()...\n"; };
	void * operator new (size_t);
	void operator delete(void *);
};

unsigned char Framis::pool[PSIZE * sizeof(Framis)];
unsigned char Framis::alloc_map[PSIZE] = { 0} ;

void * Framis::operator new(size_t sz)
{
	for(int i = 0; i < PSIZE; i++)
		if(!alloc_map[i])
		{
			out << "using block " << i << "...";
			alloc_map[i] = 1;
			return pool + (i * sizeof(Framis));
		}
	out << "out of memory" << endl;
	return 0;
}

void Framis::operator delete(void * m)
{
	if(!m)
		return;
	unsigned long block = (unsigned long)m
		- (unsigned long)pool;
	block /= sizeof(Framis);
	out << "freeing block " << endl;
	alloc_map[block] = 0;
}

int main()
{
	Framis * f[Framis::PSIZE];
	for (int i = 0; i < Framis::PSIZE; i++)
	{
		f[i] = new Framis;
	}
	new Framis;
	delete f[10];

	Framis * x = new Framis;
	delete x;
	for (int j = 0; j < Framis::PSIZE; j++)
	{
		delete f[j];
	}
	
	return 0;
}