1. String class clear/ Erase /pop_back
1.1 STD: : string: : clear
prototype: void clear() noexcept; description: clears the contents of the string to make the source string an empty string (0 characters in length). Code examples:

#include <iostream>


#include <string>

using namespace std;
int main ()
{
    string str;
    cout<<"Please enter one line, ending with a newline character."<<endl;
    getline(std::cin, str);
    cout<<"Before Clearance.str = \""<<str<<"\", str.size = "<<str.size()<<endl;
    str.clear();
    cout<<"After emptying.str = \""<<str<<"\", str.size = "<<str.size()<<endl;
    if(true == str.empty())
    {
        cout<<"The source string has been cleared."<<endl;
    }
    system("pause");
    return 0;
}
=>Please enter one line, ending with a newline character.
  hello world.
  Before clearing: str = "hello world.", str.size = 12
  Empty: str = "", str.size = 0
  The source string has been cleared.

1.2 STD: : string: : erase
archetype: string& erase (size_t pos = 0, size_t len = npos); note: delete the len characters of the source string starting with the subscript pos, and return the modified string. stereotype: iterator erase (const_iterator p); description: deletes the character pointed to by iterator p in the source string, returning the position of the iterator after deletion. stereotype: iterator erase (const_iterator first, const_iterator last); note: delete all characters in the source string iterator range [first, last], returning the position of the iterator after deletion.

#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.

1.3 STD: : string: : pop_back
Void pop_back(); void pop_back(); : removes the last character of the source string, effectively reducing its length. Code examples:

#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 

[1] network resources:
http://www.cplusplus.com/reference/string/string/clear/
http://www.cplusplus.com/reference/string/string/erase/
http://www.cplusplus.com/reference/string/string/pop_back/