README.EXT: about string termination

* README.EXT (Appendix B): add RSTRING_PTR and RSTRING_LEN.
  and NULL-termination by StringValueCStr.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45627 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

README.EXT

@@ -1081,6 +1081,15 @@ rb_float_new(f) ::
 
   double -> Float
 
+RSTRING_LEN(str) ::
+
+  String -> length of String data in bytes
+
+RSTRING_PTR(str) ::
+
+  String -> pointer to String data
+  Note that the result pointer may not be NULL-terminated
+
 StringValue(value) ::
 
   Object with #to_str -> String
@@ -1092,6 +1101,7 @@ StringValuePtr(value) ::
 StringValueCStr(value) ::
 
   Object with #to_str -> pointer to String data without NULL bytes
+  It is guaranteed that the result data is NULL-terminated
 
 rb_str_new2(s) ::
 

README.EXT.ja

@@ -1119,6 +1119,8 @@ Data_Get_Struct(data, type, sval) ::
   rb_integer_pack(value, words, numwords, wordsize, nails, flags), rb_integer_unpack(words, numwords, wordsize, nails, flags)
   NUM2DBL(value)
   rb_float_new(f)
+  RSTRING_LEN(str)
+  RSTRING_PTR(str)
   StringValue(value)
   StringValuePtr(value)
   StringValueCStr(value)