极客笔记C++ set erase()函数
C++ set erase() 函数用于从集合容器中删除与给定键相关的单个元素或一系列元素（[first, last))。因此，集合的大小将减少被删除元素的数量。
语法
void erase (iterator position); //until C++ 11
size_type erase (const value_type& val); //until C++ 11
void erase (iterator first, iterator last); //until C++ 11
iterator erase (const_iterator position); //since C++ 11
size_type erase (const value_type& val); //since C++ 11
iterator erase (const_iterator first, const_iterator last); //since C++ 11
参数
position ：指向要从集合中删除的单个元素的迭代器。
val ：要从集合中删除的值。
first ：要擦除的范围的起始位置。
last ：要擦除的范围的结束位置。
返回值
它返回一个指向被删除元素的下一个元素的迭代器，或者返回删除的元素数量。
复杂度
erase(position) ：均摊常数时间。
erase(val) ：对数时间与容器大小有关。
erase(first, last) ：与first和last之间的距离成线性关系。
迭代器的有效性
函数删除的元素所指向的迭代器、引用和指针将无效。
所有其他迭代器、指针和引用保持有效。
数据竞争
容器被修改。
被删除的元素被修改。在同时访问其他元素是安全的情况下，迭代容器中的范围是不安全的。
异常安全性
该函数不抛出异常。
如果指定了无效的范围或位置，将导致未定义行为。
示例1
让我们看一个简单的示例，通过迭代器来删除元素。
#include <iostream>
#include <set>
using namespace std;
int main ()
{
set<int> myset;
set<int>::iterator it;
myset = {10,20,30};
cout<<"Before erasing the element: \n";
for (it=myset.begin(); it!=myset.end(); ++it)
cout << *it << '\n';
it=myset.find('b');
myset.erase (*it); // erasing by iterator
cout<<"\nAfter erasing the element: \n";
for (it=myset.begin(); it!=myset.end(); ++it)
cout << *it << '\n';
return 0;
}
输出：
Before erasing the element:
10
20
30
After erasing the element:
10
20
30
在上面的示例中，元素被迭代器it擦除。
示例2
让我们看一个简单的示例，用给定的键值擦除集合中的元素:
#include <iostream>
#include <set>
using namespace std;
int main ()
{
set<int> myset;
set<int>::iterator it;
myset = {10, 20, 30, 40};
cout<<"Before erasing the element: \n";
for (it=myset.begin(); it!=myset.end(); ++it)
cout << *it<< '\n';
myset.erase (30); // erasing by value
cout<<"\nAfter erasing the element: \n";
for (it=myset.begin(); it!=myset.end(); ++it)
cout << *it<< '\n';
return 0;
}
输出：
Before erasing the element:
10
20
30
40
After erasing the element:
10
20
40
在上面的示例中，erase(value)函数使用了集合中的值30。
示例3
让我们看一个简单的示例，通过给定的范围来删除元素：
#include <iostream>
#include <set>
using namespace std;
int main ()
{
set<int> myset;
set<int>::iterator it;
myset = {10, 20, 30};
cout<<"Before erasing the element are: \n";
cout<<"Size is: "<<myset.size()<<'\n';
for (it=myset.begin(); it!=myset.end(); ++it)
cout << *it << '\n';
myset.erase ( myset.begin () , myset.end () ); // erasing by range
cout<<"\nAfter erasing the element are: \n";
cout<<"Size is: "<<myset.size();
for (it=myset.begin(); it!=myset.end(); ++it)
cout << *it << '\n';
return 0;
}
输出：
Before erasing the element are:
Size is: 3
10
20
30
After erasing the element are:
Size is: 0
在上面的示例中，使用erase(first，last)函数来删除给定范围内的元素，即从begin到end。
示例4
让我们看一个简单的示例，从集合中删除所有的奇数：
#include <set>
#include <iostream>
using namespace std;
int main()
{
set<int> m = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
// erase all odd numbers from m
cout<<"After erasing odd numbers,elements are:\n ";
for(auto it = m.begin(); it != m.end(); )
if(*it % 2 == 1)
it = m.erase(it);
else
++it;
for(auto& p : m)
cout << p << ", ";
}
输出:
After erasing odd numbers, elements are:
2, 4, 6, 8, 10, 12, 14,
在上面的示例中，所有的奇数已经被删除，并显示偶数。
示例5
让我们看另一个示例：
#include <set>
#include <string>
#include <iostream>
#include <iterator> // next() and prev() helper functions
using namespace std;
using myset = set<string>;
void printset(const myset& s) {
for (const auto& iter : s) {
cout << " [" << iter << "]";
}
cout << endl << "size() == " << s.size() << endl << endl;
}
int main()
{
myset s1;
// Fill in some data to test with, one at a time
s1.insert("Bob");
s1.insert("Robert");
s1.insert("Bert");
s1.insert("Rob");
s1.insert("Bobby");
cout << "Starting data of set s1 is:" << endl;
printset(s1);
// The 1st member function removes an element at a given position
s1.erase(next(s1.begin()));
cout << "After the 2nd element is deleted, the set s1 is:" << endl;
printset(s1);
// Fill in some data to test with, one at a time, using an intializer list
myset s2{ "meow", "hiss", "purr", "growl", "yowl" };
cout << "Starting data of set s2 is:" << endl;
printset(s2);
// The 2nd member function removes elements
// in the range [First, Last)
s2.erase(next(s2.begin()), prev(s2.end()));
cout << "After the middle elements are deleted, the set s2 is:" << endl;
printset(s2);
myset s3;
// Fill in some data to test with, one at a time, using emplace
s3.emplace("C");
s3.emplace("C#");
s3.emplace("D");
s3.emplace("D#");
s3.emplace("E");
s3.emplace("E#");
s3.emplace("F");
s3.emplace("F#");
s3.emplace("G");
s3.emplace("G#");
s3.emplace("A");
s3.emplace("A#");
s3.emplace("B");
cout << "Starting data of set s3 is:" << endl;
printset(s3);
// The 3rd member function removes elements with a given Key
myset::size_type count = s3.erase("E#");
// The 3rd member function also returns the number of elements removed
cout << "The number of elements removed from s3 is: " << count << "." << endl;
cout << "After the element with a key of \"E#\" is deleted, the set s3 is:" << endl;
printset(s3);
}
输出:
Starting data of set s1 is:
[Bert] [Bob] [Bobby] [Rob] [Robert]
size() == 5
After the 2nd element is deleted, the set s1 is:
[Bert] [Bobby] [Rob] [Robert]
size() == 4
Starting data of set s2 is:
[growl] [hiss] [meow] [purr] [yowl]
size() == 5
After the middle elements are deleted, the set s2 is:
[growl] [yowl]
size() == 2
Starting data of set s3 is:
[A] [A#] [B] [C] [C#] [D] [D#] [E] [E#] [F] [F#] [G] [G#]
size() == 13
The number of elements removed from s3 is: 1.
After the element with a key of "E#" is deleted, the set s3 is:
[A] [A#] [B] [C] [C#] [D] [D#] [E] [F] [F#] [G] [G#]
size() == 12