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map与multimap为关联容器,结构如下
map底层实现依然是rb_tree 他的data可以改,但是key不能改,因此map仍然具有自动排序的功能
我们无法使用迭代器改变元素的key(const key),但是可以改变元素的data.
map的key必须独一无二,multimap的key可以重复
map的定义函数
template <typename _Key, typename _Tp, typename _Compare = std::less<_Key>,
typename _Alloc = std::allocator<std::pair<const _Key, _Tp> > >
class map
{
public:
typedef _Key key_type;
typedef _Tp mapped_type;
typedef std::pair<const _Key, _Tp> value_type;
typedef _Compare key_compare;
typedef _Alloc allocator_type;
...
}
参数1 class key 键值key
参数2 class T data
参数3 class compare 排序key的函数 默认为less() 升序
参数4 alloc 分配器
map的基本使用
一 定义
//构造函数
map<int, int> c;
c[1] = 10;
c[2] = 20;
c[3] = 30;
c[4] = 40;
c[5] = 50;
for(auto i : c)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
//operator =
map<int, int> c1;
c1 = c;
for(auto i : c)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
二 迭代器操作 map的迭代器就是红黑树的迭代器
//迭代器操作
/*
map<int, int> c;
c.insert({pair<int, int>(1,10),pair<int, int>(2,20),pair<int, int>(3,30),pair<int, int>(4,40),pair<int, int>(5,50),pair<int, int>(6,60)});
*/
//begin()
map<int, int>::iterator iter;
iter = c.begin();
cout<< "begin(): "<<"["<< iter->first <<"] = " << iter->second <<endl;
//end()
iter = c.end();
iter--;
cout<<"end(): " <<"["<< iter->first <<"] = " << iter->second <<endl;
//rbegin()反向头迭代器
map<int, int>::reverse_iterator riter;
riter = c.rbegin();
cout << "rbegin(): "<<"["<< riter->first <<"] = " << riter->second <<endl;
//rend()反向头迭代器
riter = c.rend();
riter--;
cout << "rend(): "<<"["<< riter->first <<"] = " << riter->second <<endl;
//cbegin() const 迭代器 正向 头迭代器
map<int, int>::const_iterator citer;
citer = c.cbegin();
cout << "cbegin(): "<<"["<< citer->first <<"] = " << citer->second <<endl;
//cend() const 迭代器 反向 尾迭代器
citer = c.cend();
citer--;
cout<< "cend(): "<<"["<< citer->first <<"] = " << citer->second <<endl;
三 容量
//容量
/*
map<int, int> c;
c.insert({pair<int, int>(1,10),pair<int, int>(2,20),pair<int, int>(3,30),pair<int, int>(4,40),pair<int, int>(5,50),pair<int, int>(6,60)});
*/
//是否为kong
cout << "empty: " << c.empty() <<endl;
//元素个数
cout << "size: " << c.size() <<endl;
//最大容量
cout << "max_size: " << c.max_size() <<endl;
四 基本操作
//基本操作
/*
map<int, int> c;
c.insert({pair<int, int>(1,10),pair<int, int>(2,20),pair<int, int>(3,30),pair<int, int>(4,40),pair<int, int>(5,50),pair<int, int>(6,60)});
*/
//operator[] 这个和其他容器的operator有些不同,如果[index] 的index(key) 在map中存在则直接返回该key对应的data ,如果不存在则想该位置插入默认值
cout << "operator[]: " << c[1] << endl;
cout << "operator[]: " << c[10] << endl; //这时你会发现 map自动插入一个c[10]
for(auto i : c)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
//at() 取data
cout<< "at(): " << c.at(3) << endl;
//插入insert() map 不允许key重复 插入重复key 不会报错但插入不成功
c.insert(pair<int, int>(6, 15));
cout <<"insetr(): ";
for(auto i : c)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
map<int, int> c_insert;
map<int, int>::iterator insert_iter = c_insert.begin();
c_insert.insert(insert_iter,pair<int, int>(100, 10000));
cout <<"insetr(): ";
for(auto i : c_insert)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
//删除
map<int,int>::iterator erase_iter = c.begin();
c.erase(erase_iter);
cout <<"erase(): ";
for(auto i : c)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
//指定下表删除
c.erase(10);
cout <<"erase(): ";
for(auto i : c)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
//指定元素删除
erase_iter = c.find(6);
if(erase_iter != c.end())
{
cout<<"found index: "<< erase_iter->first <<endl;
c.erase(erase_iter);
}
else{
cout<< "Not found" <<endl;
}
for(auto i : c)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
//交换swap
map<int, int> c_swap1;
c_swap1.insert({pair<int, int>(1,10),pair<int, int>(2,20),pair<int, int>(3,30),pair<int, int>(4,40),pair<int, int>(5,50),pair<int, int>(6,60)});
map<int, int> c_swap2;
cout<<"swap() before: "<<endl;
cout<<"c_swap1: ";
for(auto i : c_swap1)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
cout<<"c_swap2: ";
for(auto i : c_swap2)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
cout<<"swap() after: ";
c_swap2.swap(c_swap1);
cout<<"c_swap1: ";
for(auto i : c_swap1)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
cout<<"c_swap2: ";
for(auto i : c_swap2)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
//清除clear
c_insert.clear();
cout <<"clear(): ";
for(auto i : c_insert)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
//elements() 插入 如果存在什么也不做 如果不存在插入
map<int, int>::iterator element_iter = c_swap2.begin();
auto xxx = c_swap2.emplace(pair<int, int>(7,60));
if(xxx.second)
{
cout << "不存在" <<endl;
}
else
{
cout<< "存在" <<endl;
}
cout <<"elements(): ";
for(auto i : c_swap2)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
//emplace_hint() 插入
element_iter = c.emplace_hint(element_iter, pair<int, int>(7,60));
cout <<"emplace_hint(): ";
if(element_iter != c_swap2.end())
{
cout<< "存在" <<endl;
}
else{
cout << "不存在" <<endl;
}
五 操作函数
//函数
/*
map<int, int> c;
c.insert({pair<int, int>(1,10),pair<int, int>(2,20),pair<int, int>(3,30),pair<int, int>(4,40),pair<int, int>(5,50),pair<int, int>(6,60)});
*/
//key_comp 返回key排序的函数 返回仿函数
cout<<"key_comp(): " << c.key_comp()(1,2) <<endl; //会返回1 因为1<2
cout<<"key_comp(): " << c.key_comp()(2,1) <<endl; //会返回0 因为2>1
cout<<"key_comp(): " << c.key_comp()(1,1) <<endl; //会返回0 因为1=1
//value_comp 返回取value和key数据包中的 取key函数 返回仿函数
pair<int,int> value_comp_pair = *c.begin();
iter = c.begin();
cout << c.value_comp()(*iter++,value_comp_pair) << endl;
六 算法
//算法
/*
map<int, int> c;
c.insert({pair<int, int>(1,10),pair<int, int>(2,20),pair<int, int>(3,30),pair<int, int>(4,40),pair<int, int>(5,50),pair<int, int>(6,60)});
*/
//find() 指定key 返回对应pair
cout <<"find(1): " << c.find(1)->second << endl;;
//count() key出现的次数
cout <<"count(1): " << c.count(1)<< endl;;
c.erase(4);
//lower_bound 返回键值>=给定元素的第一个位置
auto lower_boundObj = c.lower_bound(8);
if(lower_boundObj->first)
cout<<lower_boundObj->first<<endl;
else
cout<< "Not found lower_boundObj" << endl;
for(auto i : c)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
//upper_bound 返回键值>给定元素的第一个位置
auto upper_boundObj = c.upper_bound(4);
if(upper_boundObj->first)
cout<<upper_boundObj->first<<endl;
else
cout<< "Not found upper_bound" << endl;
for(auto i : c)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
//equal_range()返回该元素所在区间(闭区间),返回值是一个pair<iterator, iterator>类型,first代表所在区间的起点迭代器,second表示所在区间的终点迭代器
auto equal_rangeObj = c.equal_range(3);
if(equal_rangeObj.first->first)
{
cout<<equal_rangeObj.first->first<<endl;
}
else
cout<< "NOT equal_rangeObj.first" << endl;
if(equal_rangeObj.second->second)
{
cout<<equal_rangeObj.second->first<<endl;
}
else
cout<< "NOT second" << endl;
七 自定义比较函数 map 默认为升序 改为降序
class my_compare_
{
public:
bool operator()(int a, int b)
{
return a > b;
}
};
int main(int argc, char *argv[])
{
map<int, int, my_compare_> c;
c.insert({pair<int, int>(1,10),pair<int, int>(2,20),pair<int, int>(3,30),pair<int, int>(4,40),pair<int, int>(5,50),pair<int, int>(6,60)});
for(auto i : c)
{
cout<<"["<< i.first <<"] = " << i.second <<" ";
}
cout << endl;
return 0;
}
时间： 2024-12-28 09:40:55