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");
}
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