容器之分类与各种测试（四）——map

map和set的区别在于，前者key和value是分开的，前者的key不会重复，value可以重复；后者的key即为value，后者的value不允许重复。还有，map在插入时可以使用 [ ]进行（看插入时代码），其采用了看起来像是数组插值的方法进行元素的插入。

 例程

#include<stdexcept>
#include<string>
#include<cstdlib>
#include<cstdio>
#include<algorithm>
#include<iostream>
#include<ctime>
#include<map>
using namespace std;
long get_a_target_long()
{
	long target = 0;
	cout<<"target(0~"<<RAND_MAX<<"):";
	cin>>target;
	return target;
}
string get_a_target_string()
{
	long target = 0;
	char buf[10];
	cout<<"target(0~"<<RAND_MAX<<"):";
	cin>>target;
	snprintf(buf, 10, "%ld", target);
	return string(buf);
}
int compareLongs(const void* a, const void* b)
{
	return (*(long*)a - *(long*)b);
}

int compareStrings(const void *a, const void *b)
{
	if(*(string*)a > *(string*)b)
		return 1;
	else if(*(string*)a < *(string*)b)
		return -1;
	else
		return 0;
}
void test_map(long& value)
{
	cout << "\ntest_map().......... \n";

	map<long, string> c;
	char buf[10];

	clock_t timeStart = clock();
	for(long i=0; i< value; ++i)
	{
		try
		{
			snprintf(buf, 10, "%d", rand());
			c[i] = string(buf);  //表现上像是数组插入值，实际上在其内部会自动将i 和 buf 合成为一个pair进行插入
		}
		catch(exception& p)
		{
			cout << "i=" << i << " " << p.what() << endl;
			abort();
		}
	}
	cout << "milli-seconds : " << (clock()-timeStart) << endl;
	cout << "map.size()= " << c.size() << endl;	//元素个数
	cout << "map.max_size()= " << c.max_size() << endl;

	long target = get_a_target_long();
	timeStart = clock();
	auto pItem = c.find(target);
	cout << "c.find(), milli-seconds : " << (clock()-timeStart) << endl;
	if (pItem != c.end())
		cout << "found, value=" << (*pItem).second << endl;
	else
		cout << "not found! " << endl;
}
int main()
{
	long int value;
	cout<<"how many elements: ";
	cin>>value;
	test_map(value);
	return 0;
}

 运行结果