find_first_of

  #include <string>
  size_type find_first_of( const string &str, size_type index = 0 );
  size_type find_first_of( const char* str, size_type index = 0 );
  size_type find_first_of( const char* str, size_type index, size_type num );
  size_type find_first_of( char ch, size_type index = 0 );

The find_first_of() function either:

• returns the index of the first character within the current string that matches any character in str, beginning the search at index, string::npos if nothing is found,
• searches the current string, beginning at index, for any of the first num characters in str, returning the index in the current string of the first character found, or string::npos if no characters match,
• or returns the index of the first occurrence of ch in the current string, starting the search at index, string::npos if nothing is found.