friend declaration can't have default parameters

Index: ddd/strclass.h
--- ddd/strclass.h.orig
+++ ddd/strclass.h
@@ -543,7 +543,15 @@ class subString (public)
     bool OK() const; 
 };
 
+class string;
 
+string common_prefix(const string& x, const string& y, 
+				int startpos = 0);
+string common_suffix(const string& x, const string& y, 
+				int startpos = -1);
+int readline(std::istream& s, string& x, char terminator = '\n',
+			int discard_terminator = 1);
+
 class string
 {
     friend class subString;
@@ -810,10 +818,8 @@ class string (public)
     friend int split(const string& x, string *res, int maxn, 
 		     const regex& sep);
 
-    friend string common_prefix(const string& x, const string& y, 
-				int startpos = 0);
-    friend string common_suffix(const string& x, const string& y, 
-				int startpos = -1);
+    friend string common_prefix(const string& x, const string& y, int startpos);
+    friend string common_suffix(const string& x, const string& y, int startpos);
     friend string replicate(char c, int n);
     friend string replicate(const string& y, int n);
     friend string join(const string *src, int n, const string& sep);
@@ -864,8 +870,7 @@ class string (public)
     friend std::istream& operator>>(std::istream& s, string& x);
 
     friend int readline(std::istream& s, string& x, 
-			char terminator = '\n',
-			int discard_terminator = 1);
+			char terminator, int discard_terminator);
 
     // Status
     unsigned int length() const;