string::substr C++用法

std::string::substr

string substr (size_t pos = 0, size_t len = npos) const;

Generate substring

Returns a newly constructed  string object with its value initialized to a copy of a substring of this object.

The substring is the portion of the object that starts at character position  pos and spans  len characters.

Parameters

pos

Position of the first character to be copied as a substring.
If this is greater than the  string length, it throws  out_of_range.
Note: The first character is denoted by a value of  0 (not  1).

len

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

size_t is an unsigned integral type.