Changeset 4134 in vbox for trunk/include/VBox/com

Timestamp:

Aug 13, 2007 4:35:46 PM (18 years ago)

Author:

vboxsync

svn:sync-xref-src-repo-rev:

23613

Message:

Main: Add Utf8StrFmtVA to resolve the dangerous ambiguity of ellipsis and va_list.

File:

• trunk/include/VBox/com/string.h (modified) (3 diffs)

trunk/include/VBox/com/string.h

@@ -507 +507 @@
      *
      *  @param format   printf-like format string (in UTF-8 encoding)
-     *  @param args     list of arguments for the format string
-     */
-    explicit Utf8StrFmt (const char *format, va_list args) { init (format, args); }
+     *  @param ...      list of the arguments for the format string
+     */
+    explicit Utf8StrFmt (const char *format, ...)
+    {
+        va_list args;
+        va_start (args, format);
+        init (format, args);
+        va_end (args);
+    }
+
+protected:
+
+    Utf8StrFmt() {}
+
+    void init (const char *format, va_list args);
+
+private:
+
+    static DECLCALLBACK(size_t) strOutput (void *pvArg, const char *pachChars,
+                                           size_t cbChars);
+};
+
+/**
+ *  This class is a vprintf-like formatter for Utf8Str strings. It is
+ *  identical to Utf8StrFmt except that its constructor takes a va_list
+ *  argument instead of ellipsis.
+ *
+ *  Note that a separate class is necessary because va_list is defined as
+ *  |char *| on most platforms. For this reason, if we had two overloaded
+ *  constructors in Utf8StrFmt (one taking ellipsis and another one taking
+ *  va_list) then composing a constructor call using exactly two |char *|
+ *  arguments would cause the compiler to use the va_list overload instead of
+ *  the ellipsis one which is obviously wrong. The compiler would choose
+ *  va_list because ellipsis has the lowest rank when it comes to resolving
+ *  overloads, as opposed to va_list which is an exact match for |char *|.
+ */
+class Utf8StrFmtVA : public Utf8StrFmt
+{
+public:
 
     /**
@@ -516 +552 @@
      *
      *  @param format   printf-like format string (in UTF-8 encoding)
-     *  @param ...      list of the arguments for the format string
-     *
-     *  @note  Be extremely careful when passing exactly one argument in the
-     *         ellipsis. If this is a string the C++ could decide to use the
-     *         other constructor since va_list is defined as char * on some
-     *         platforms. If unsure, add an extra dummy argument.
-     */
-    explicit Utf8StrFmt (const char *format, ...)
-    {
-        va_list args;
-        va_start (args, format);
-        init (format, args);
-        va_end (args);
-    }
-
-private:
-
-    void init (const char *format, va_list args);
-
-    static DECLCALLBACK(size_t) strOutput (void *pvArg, const char *pachChars,
-                                           size_t cbChars);
+     *  @param args     list of arguments for the format string
+     */
+    Utf8StrFmtVA (const char *format, va_list args) { init (format, args); }
 };
 
@@ -542 +560 @@
 
 #endif
-