[Assorted-commits] SF.net SVN: assorted: [672] sandbox/trunk/src/cc/conversions.cc

[<yan...@us...>]

Revision: 672
          http://assorted.svn.sourceforge.net/assorted/?rev=672&view=rev
Author:   yangzhang
Date:     2008-04-21 12:52:35 -0700 (Mon, 21 Apr 2008)

Log Message:
-----------
conversions demo

Modified Paths:
--------------
    sandbox/trunk/src/cc/conversions.cc

Modified: sandbox/trunk/src/cc/conversions.cc
===================================================================
--- sandbox/trunk/src/cc/conversions.cc	2008-04-21 19:52:14 UTC (rev 671)
+++ sandbox/trunk/src/cc/conversions.cc	2008-04-21 19:52:35 UTC (rev 672)
@@ -1,15 +1,38 @@
+// Demo of conversions.
+
 #include <iostream>
+#include <string>
 
 using namespace std;
 
+void f(const string& str) {
+  cout << "f(const string& str = " << str.c_str() << ")" << endl;
+}
+
+void f(bool b) {
+  cout << "f(bool b = " << b << ")" << endl;
+}
+
 int
 main()
 {
-  // This doesn't compile.
+  // This lexical conversion doesn't compile.
   // int i("321");
 
   // This doesn't work as expected; always outputs 1.
   bool b("false");
   cout << b << endl;
+
+  // What happens is that C++ can't find an exact match for a "const char*" parameter. It looks at all the available constructors, and looks at which ones are possible. There are two:
+  //
+  // 1. bool via a pointer -> bool conversion
+  // 2. std::string via the std::string(const char*) constructor
+  //
+  // 1. is a "standard conversion sequence"
+  // 2. is a "user-defined conversion sequence," since it is a function.
+  //
+  // C++ decides the "best" function to call by ranking all the possible calls. Standard conversions rank better than user-defined conversions, so #1 is called. 
+  f(string("hello"));
+  f("hello");
 }
 


This was sent by the SourceForge.net collaborative development platform, the world's largest Open Source development site.