std::map::map
STD：：map：：map
| | (1) | |
|---|---|---|
| explicit map( const Compare& comp = Compare(), const Allocator& alloc = Allocator() | (until C++14) | |
| map() : map( Compare() ) {} explicit map( const Compare& comp, const Allocator& alloc = Allocator() | (since C++14) | |
| explicit map( const Allocator& alloc | (1) | (since C++11) |
| | (2) | |
| template< class InputIterator > map( InputIterator first, InputIterator last, const Compare& comp = Compare(), const Allocator& alloc = Allocator() | | |
| template< class InputIterator > map( InputIterator first, InputIterator last, const Allocator& alloc | (since C++14) | |
| map( const map& other | (3) | |
| map( const map& other, const Allocator& alloc | (3) | (since C++11) |
| map( map&& other | (4) | (since C++11) |
| map( map&& other, const Allocator& alloc | (4) | (since C++11) |
| | (5) | |
| map( std::initializer_list<value_type> init, const Compare& comp = Compare(), const Allocator& alloc = Allocator() | (since C++11) | |
| map( std::initializer_list<value_type> init, const Allocator& | (since C++14) |
从各种数据源构造新容器，并可选择使用用户提供的分配器。alloc或比较函数对象comp...
1%29默认构造函数。构造空容器。
2%29构造包含范围内容的容器。[first, last)如果区域中的多个元素具有比较等效的键，则未指定插入了%28挂起的元素。LWG2844%29
3%29复制构造函数。的内容的副本构造容器。other.如果alloc不提供，则通过调用std::allocator_traits<allocator_type>::select_on_container_copy_construction(other.get_allocator())...
4%29移动构造函数。的内容构造容器。other使用移动语义。如果alloc如果不提供分配器，则通过移动构造从属于other...
5%29使用初始化程序列表的内容构造容器。init如果区域中的多个元素具有比较等效的键，则未指定插入了%28挂起的元素。LWG2844%29
参数
| alloc | - | allocator to use for all memory allocations of this container |
|---|---|---|
| comp | - | comparison function object to use for all comparisons of keys |
| first, last | - | the range to copy the elements from |
| other | - | another container to be used as source to initialize the elements of the container with |
| init | - | initializer list to initialize the elements of the container with |
类型要求
-输入器必须符合输入器的要求。
-比较必须符合比较的要求。
-分配器必须符合分配器的要求。
复杂性
1%29常数
2%29N日志%28N%29N =std::distance(first, last)一般情况下，线性在N如果范围已经按value_comp()...
3%29线性other
4%29常数。如果alloc被赋予和alloc != other.get_allocator()，然后是线性的。
5%29N日志%28N%29N = init.size())一般情况下，线性在N如果init已按value_comp()...
注记
在容器移动构造%28重载%284%29%29之后，引用、指针和迭代器%28---other保持有效，但引用当前在*this.现行标准通过第23.2.1节中的总括声明作出这一保证。集装箱。所需经费/12，目前正在考虑通过以下方式提供更直接的担保：lwg 2321...
例
二次
#include <iostream>
#include <string>
#include <iomanip>
#include <map>
template<typename Map>
void print_map(Map& m)
{
std::cout << '{';
for(auto& p: m)
std::cout << p.first << ':' << p.second << ' ';
std::cout << "}\n";
}
struct Point { double x, y; };
struct PointCmp {
bool operator()(const Point& lhs, const Point& rhs) const {
return lhs.x < rhs.x; // NB. intentionally ignores y
}
};
int main()
{
// (1) Default constructor
std::map<std::string, int> map1;
map1["something"] = 69;
map1["anything"] = 199;
map1["that thing"] = 50;
std::cout << "map1 = "; print_map(map1
// (2) Range constructor
std::map<std::string, int> iter(map1.find("anything"), map1.end()
std::cout << "\niter = "; print_map(iter
std::cout << "map1 = "; print_map(map1
// (3) Copy constructor
std::map<std::string, int> copied(map1
std::cout << "\ncopied = "; print_map(copied
std::cout << "map1 = "; print_map(map1
// (4) Move constructor
std::map<std::string, int> moved(std::move(map1)
std::cout << "\nmoved = "; print_map(moved
std::cout << "map1 = "; print_map(map1
// (5) Initializer list constructor
const std::map<std::string, int> init {
{"this", 100},
{"can", 100},
{"be", 100},
{"const", 100},
};
std::cout << "\ninit = "; print_map(init
// Custom Key class option 1:
// Use a comparison struct
std::map<Point, double, PointCmp> mag = {
{ {5, -12}, 13 },
{ {3, 4}, 5 },
{ {-8, -15}, 17 }
};
for(auto p : mag)
std::cout << "The magnitude of (" << p.first.x
<< ", " << p.first.y << ") is "
<< p.second << '\n';
// Custom Key class option 2:
// Use a comparison lambda
// This lambda sorts points according to their magnitudes, where note that
// these magnitudes are taken from the local variable mag
auto cmpLambda = [&mag](const Point &lhs, const Point &rhs) { return mag[lhs] < mag[rhs]; };
//You could also use a lambda that is not dependent on local variables, like this:
//auto cmpLambda = [](const Point &lhs, const Point &rhs) { return lhs.y < rhs.y; };
std::map<Point, double, decltype(cmpLambda)> magy(cmpLambda
//Various ways of inserting elements:
magy.insert(std::pair<Point, double>{5, -12}, 13)
magy.insert{ {3, 4}, 5}
magy.insert{Point{-8.0, -15.0}, 17}
std::cout << '\n';
for(auto p : magy)
std::cout << "The magnitude of (" << p.first.x
<< ", " << p.first.y << ") is "
<< p.second << '\n';
}
二次
产出：
二次
map1 = {anything:199 something:69 that thing:50 }
iter = {anything:199 something:69 that thing:50 }
map1 = {anything:199 something:69 that thing:50 }
copied = {anything:199 something:69 that thing:50 }
map1 = {anything:199 something:69 that thing:50 }
moved = {anything:199 something:69 that thing:50 }
map1 = {}
init = {be:100 can:100 const:100 this:100 }
The magnitude of (-8, -15) is 17
The magnitude of (3, 4) is 5
The magnitude of (5, -12) is 13
The magnitude of (3, 4) is 5
The magnitude of (5, -12) is 13
The magnitude of (-8, -15) is 17
二次
另见
| operator= | assigns values to the container (public member function) |
|---|
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