string类的clear/erase/pop_back

clear：清空字符串 

#include <iostream>


#include <string>

using namespace std;
int main ()
{
    string str;
    cout<<"请输入一行字符，以换行符结束："<<endl;
    getline(std::cin, str);
    cout<<"清空前：str = ""<<str<<"", str.size = "<<str.size()<<endl;
    str.clear();
    cout<<"清空后：str = ""<<str<<"", str.size = "<<str.size()<<endl;
    if(true == str.empty())
    {
        cout<<"源字符串已被清空"<<endl;
    }
    system("pause");
    return 0;
}
 ;=>请输入一行字符，以换行符结束：
 ; hello world.
 ;清空前：str = "hello world.", str.size = 12
  ;清空后：str = "", str.size = 0
 ; 源字符串已被清空

std::string::erase

原型：string& erase (size_t pos = 0, size_t len = npos);

说明：删除源字符串以下标为pos开始的len个字符，返回修改后的字符串。

原型：iterator erase (const_iterator p);

说明：删除源字符串中迭代器p指向的字符，返回删除后迭代器的位置。

原型：iterator erase (const_iterator first, const_iterator last);

说明：删除源字符串迭代器范围为[first，last）内的所有字符，返回删除后迭代器的位置

#include <iostream>
#include <string>

using namespace std;
int main ()
{
    string str("This is an example sentence.");
    cout<<str<<endl;

    str.erase(10, 8);                        
    cout<<str<<endl;

    str.erase(str.begin()+9);           
    cout<<str<<endl;

    str.erase(str.begin()+5, str.end()-9);  
    cout<<str<<endl;

    system("pause");
    return 0;
}
=>This is an example sentence.
  This is an sentence.
  This is a sentence.
  This sentence.

POP_BACK:删除源字符串的最后一个字符，有效减少它的长度。

#include <iostream>


#include <string>

using namespace std;
int main ()
{
    string str("hello world!");
    str.pop_back();
    cout<<str<<endl;

    system("pause");
    return 0;
}
=>hello world