Standard Template Library (STL) -
std::map::size
std::map::size
public member function - 公开成员函数
1. std::map::size
C++98
size_type size() const;
C++11
size_type size() const noexcept;
Return container size - 返回容纳的元素数
Returns the number of elements in the map container.
返回 map 容器中的元素数。
返回容器中的元素数，即 std::distance(begin(), end()) 。
2. Parameters
none - 无
3. Return value
The number of elements in the container.
容器中的元素数量。
Member type size_type is an unsigned integral type (unsigned int).
4. Examples
4.1 std::map::size
//============================================================================
// Name : std::map::size
// Author : Yongqiang Cheng
// Version : Version 1.0.0
// Copyright : Copyright (c) 2019 Yongqiang Cheng
// Description : Hello World in C++, Ansi-style
//============================================================================
#include <iostream>
#include <map>
int main()
{
std::map<char, int> map_data;
map_data['a'] = 101;
map_data['b'] = 202;
map_data['c'] = 302;
std::cout << "map_data.size() is " << map_data.size() << '\n';
return 0;
}
map_data.size() is 3
4.2 std::map::size
//============================================================================
// Name : std::map::size
// Author : Yongqiang Cheng
// Version : Version 1.0.0
// Copyright : Copyright (c) 2019 Yongqiang Cheng
// Description : Hello World in C++, Ansi-style
//============================================================================
#include <map>
#include <iostream>
int main()
{
std::map<int,char> nums {{1, 'a'}, {3, 'b'}, {5, 'c'}, {7, 'd'}};
std::cout << "nums contains " << nums.size() << " elements.\n";
}
19:34:26 **** Build of configuration Debug for project hello_world ****
make all
Building file: ../src/hello_world.cpp
Invoking: GCC C++ Compiler
g++ -std=c++0x -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/hello_world.d" -MT"src/hello_world.o" -o "src/hello_world.o" "../src/hello_world.cpp"
Finished building: ../src/hello_world.cpp
Building target: hello_world
Invoking: GCC C++ Linker
g++ -o "hello_world" ./src/hello_world.o
Finished building target: hello_world
19:34:27 Build Finished (took 778ms)
nums contains 4 elements.
5. Complexity - 复杂度
Constant. - 常数。
6. Iterator validity - 迭代器有效性
No changes.
7. Data races - 数据竞争
The container is accessed. - 容器被访问。
No elements are accessed: concurrently accessing or modifying them is safe.
没有元素被访问：同时访问或修改它们是安全的。
8. Exception safety - 异常安全性
No-throw guarantee: this member function never throws exceptions.
No-throw guarantee：此成员函数从不抛出异常。
References
