Map使用之关联数组
背景：在C++ Standard Library中，Map容器使用pair(Key/Value)存储元素，而且不允许重复元素。如果给定一个Key，存在着唯一的对应的Value，Key与Value存在着某种关联，由此，可将Map作为关联数组使用。现举例如下
Test OS: Windows 7
Test IDE: Visual Studio 2005
Code Example:
[cpp]
#include "stdafx.h"
#include <iostream>
#include <map>
#include <string>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
/* Create map / associative map
* - keys are strings
* - values are float
*/
typedef map<string, float> StringFloatMap;
// create empty container
StringFloatMap stocks;
// insert some elements
stocks["TXKG"] = 276.50;
stocks["GOOG"] = 700.34;
stocks["AAPL"] = 498.26;
stocks["BMW"] = 823.23;
stocks["NONE"] = 0.72;
stocks["NOKIA"] = 12.25;
// print all elements
StringFloatMap::iterator pos;
for(pos = stocks.begin(); pos != stocks.end(); ++pos)
{
cout << "stock:" << pos->first << "\t"
<< "price:" << pos->second << endl;
}
cout << endl;
// all stocks doubled
for(pos = stocks.begin(); pos != stocks.end(); ++pos)
{
pos->second *= 2;
}
// print all elements
for(pos = stocks.begin(); pos != stocks.end(); ++pos)
{
cout << "stock:" << pos->first << "\t"
<< "price:" << pos->second << endl;
}
cout << endl;
// rename key from "AAPL" to "APPLE"
stocks["APPLE"] = stocks["AAPL"];
stocks.erase("AAPL");
// print all elements
for(pos = stocks.begin(); pos != stocks.end(); ++pos)
{
cout << "stock:" << pos->first << "\t"
<< "price:" << pos->second << endl;
}
cout << endl;
system("pause");
return 0;
}
#include "stdafx.h"
#include <iostream>
#include <map>
#include <string>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
/* Create map / associative map
* - keys are strings
* - values are float
*/
typedef map<string, float> StringFloatMap;
// create empty container
StringFloatMap stocks;
// insert some elements
stocks["TXKG"] = 276.50;
stocks["GOOG"] = 700.34;
stocks["AAPL"] = 498.26;
stocks["BMW"] = 823.23;
stocks["NONE"] = 0.72;
stocks["NOKIA"] = 12.25;
// print all elements
StringFloatMap::iterator pos;
for(pos = stocks.begin(); pos != stocks.end(); ++pos)
{
cout << "stock:" << pos->first << "\t"
<< "price:" << pos->second << endl;
}
cout << endl;
// all stocks doubled
for(pos = stocks.begin(); pos != stocks.end(); ++pos)
{
pos->second *= 2;
}
// print all elements
for(pos = stocks.begin(); pos != stocks.end(); ++pos)
{
cout << "stock:" << pos->first << "\t"
<< "price:" << pos->second << endl;
}
cout << endl;
// rename key from "AAPL" to "APPLE"
stocks["APPLE"] = stocks["AAPL"];
stocks.erase("AAPL");
// print all elements
for(pos = stocks.begin(); pos != stocks.end(); ++pos)
{
cout << "stock:" << pos->first << "\t"
<< "price:" << pos->second << endl;
}
cout << endl;
system("pause");
return 0;
}
Test Result as follow:
可见，使用pair第一元素类型作为下标，寻址到该Key对应的Value的引用，可以很方便地操纵元素。
这里需要注意：
当使用Key作为下标时，如果Map中已经存在该元素，则返回该元素Value的引用，如果不存在，则会插入一个以下标为Key的元素，并使用Value对应数据类型的Default构造函数初始化Value。即上例中中如果使用语句stocks["abcd"] = 5.0,则插入Key为“abcd”的元素，并以float 0 初始化，紧接着，将该元素的Value赋值为5.0。
补充：软件开发 , C++ ,
