一個超好用的c++網站：http://www.cplusplus.com/reference/string/string/erase/

一、string類的函數

1.string& erase (size_t pos = 0, size_t len = npos);

pos：

Position of the first character to be erased.
If this is greater than the string length, it throws out_of_range.
Note: The first character in str is denoted by a value of 0

Number of characters to erase (if the string is shorter, as many characters as possible are erased).
A value of string::npos indicates all characters until the end of the string.

c/c++的常用函數和STL使用