Added FORMAT$ command to runtime

demo.cpp

@@ -71,6 +71,10 @@ MAIN
   PRINT ( "SAVEFILE()" );
   SAVEFILE(fileContents,"output.txt");
   PRINT ( "Contents saved to 'output.txt'");
+  PRINT ();
+
+  PRINT ( "FORMAT$(\"%d %s\", 10, \"TEN\")" );
+  PRINT ( FORMAT$("%d %s",10, "TEN") );
 
 
 ENDMAIN

runtime.inc

@@ -14,10 +14,33 @@ DECLARE FUNCTION CSTRING ENC$ (CSTRING,INT=34,INT=34);
 DECLARE FUNCTION CSTRING REVERSE$ (CSTRING);
 DECLARE FUNCTION CSTRING REPLACE$ (CSTRING subject, CONSTANT CSTRING& search, CONSTANT CSTRING& replace);
 DECLARE FUNCTION INT VAL (CSTRING);
+DECLARE FUNCTION CSTRING FORMAT$ (CONSTANT CSTRING &fmt, ...);
 DECLARE SUB PRINT (CSTRING);
 DECLARE SUB SAVEFILE(CSTRING src, CSTRING fname);
 
 
+FUNCTION CSTRING FORMAT$ (CONSTANT CSTRING &fmt, ...) BEGIN
+    DIM AS VECTOR<char> str(100,'\0');
+    DIM AS va_list ap;
+    DIM AS INT n;
+
+    WHILE (TRUE) {
+        va_start(ap, fmt);
+        n = vsnprintf(str.data(), str.size(), fmt.c_str(), ap);
+        va_end(ap);
+        IF ((n > -1) AND (size_t(n) < str.size())) THEN
+            RETURN str.data();
+        ENDIF
+        IF (n > -1) THEN
+            str.resize( n + 1 );
+        ELSE
+            str.resize( str.size() * 2);
+        ENDIF
+    WEND
+
+    RETURN str.data();
+ENDFUNCTION
+
 FUNCTION CSTRING REVERSE$ (CSTRING src) BEGIN
     RETURN CSTRING( src.rbegin(),src.rend() );
 ENDFUNCTION