#include <string>
  size_type find_last_of( const string& str, size_type index = npos );
  size_type find_last_of( const char* str, size_type index = npos );
  size_type find_last_of( const char* str, size_type index, size_type num );
  size_type find_last_of( char ch, size_type index = npos );

The find_last_of() function either:

• does a reverse search from index, returning the index of the first character within the current string that matches any character in str, or string::npos if nothing is found,
• does a reverse search from index, returning the index of the first character within the current string that matches any character in str, and searching at most num characters, or string::npos if nothing is found,
• or does a reverse search from index, returning the index of the first occurrence of ch in the current string, string::npos if nothing is found.