Add wxString::ToStdString() and ToStdWstring().

These trivial helper functions are available in all builds (provided that
wxUSE_STD_STRING is not explicitly set to non-default 0 value) unlike implicit
conversions to std::[w]string which are only available when wxUSE_STL==1.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63938 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -440,6 +440,7 @@ All:
 - Don't crash when input is empty in wxFileConfig ctor (Lukasz Michalski).
 - Correct wxSocket::Peek() to not block (Anders Larsen).
 - Added IEC and SI units support to GetHumanReadableSize() (Julien Weinzorn).
+- Add convenient wxString::ToStd{String,Wstring}() helpers.
 
 Unix:
 

include/wx/string.h

@@ -1341,14 +1341,18 @@ public:
 
   // Unlike ctor from std::string, we provide conversion to std::string only
   // if wxUSE_STL and not merely wxUSE_STD_STRING (which is on by default),
-  // because it conflicts with operator const char/wchar_t*:
+  // because it conflicts with operator const char/wchar_t* but we still
-#if wxUSE_STL
+  // provide explicit conversions to std::[w]string for convenience in any case
+#if wxUSE_STD_STRING
+  // We can avoid a copy if we already use this string type internally,
+  // otherwise we create a copy on the fly:
   #if wxUSE_UNICODE_WCHAR && wxUSE_STL_BASED_WXSTRING
-    // wxStringImpl is std::string in the encoding we want
+    #define wxStringToStdWstringRetType const wxStdWideString&
-    operator const wxStdWideString&() const { return m_impl; }
+    const wxStdWideString& ToStdWstring() const { return m_impl; }
   #else
     // wxStringImpl is either not std::string or needs conversion
-    operator wxStdWideString() const
+    #define wxStringToStdWstringRetType wxStdWideString
+    wxStdWideString ToStdWstring() const
     {
         wxScopedWCharBuffer buf(wc_str());
         return wxStdWideString(buf.data(), buf.length());
@@ -1357,17 +1361,31 @@ public:
 
   #if (!wxUSE_UNICODE || wxUSE_UTF8_LOCALE_ONLY) && wxUSE_STL_BASED_WXSTRING
     // wxStringImpl is std::string in the encoding we want
-    operator const std::string&() const { return m_impl; }
+    #define wxStringToStdStringRetType const std::string&
+    const std::string& ToStdString() const { return m_impl; }
   #else
     // wxStringImpl is either not std::string or needs conversion
-    operator std::string() const
+    #define wxStringToStdStringRetType std::string
+    std::string ToStdString() const
     {
         wxScopedCharBuffer buf(mb_str());
         return std::string(buf.data(), buf.length());
     }
   #endif
+
+#if wxUSE_STL
+  // In wxUSE_STL case we also provide implicit conversions as there is no
+  // ambiguity with the const char/wchar_t* ones as they are disabled in this
+  // build (for consistency with std::basic_string<>)
+  operator wxStringToStdStringRetType() const { return ToStdString(); }
+  operator wxStringToStdWstringRetType() const { return ToStdWstring(); }
 #endif // wxUSE_STL
 
+#undef wxStringToStdStringRetType
+#undef wxStringToStdWstringRetType
+
+#endif // wxUSE_STD_STRING
+
   wxString Clone() const
   {
       // make a deep copy of the string, i.e. the returned string will have

interface/wx/string.h

@@ -181,11 +181,15 @@ public:
     /**
        Constructs a string from @a str using the using the current locale encoding
        to convert it to Unicode (wxConvLibc).
+
+       @see ToStdString()
     */
     wxString(const std::string& str);
 
     /**
        Constructs a string from @a str.
+
+       @see ToStdWstring()
     */
     wxString(const std::wstring& str);
 
@@ -509,6 +513,36 @@ public:
     */
     const wxCharBuffer ToAscii() const;
 
+    /**
+        Return the string as an std::string in current locale encoding.
+
+        Note that if the conversion of (Unicode) string contents to the current
+        locale fails, the return string will be empty. Be sure to check for
+        this to avoid silent data loss.
+
+        Instead of using this function it's also possible to write
+        @code
+        std::string s;
+        wxString wxs;
+        ...
+        s = std::string(wxs);
+        @endcode
+        but using ToStdString() may make the code more clear.
+
+        @since 2.9.1
+    */
+    std::string ToStdString() const;
+
+    /**
+        Return the string as an std::wstring.
+
+        Unlike ToStdString(), there is no danger of data loss when using this
+        function.
+
+        @since 2.9.1
+    */
+    std::wstring ToStdWstring() const;
+
     /**
         Same as utf8_str().
     */

tests/strings/stdstrings.cpp

@@ -559,15 +559,22 @@ void StdStringTestCase::StdConversion()
 
     wxString s4("hello");
 
-    // wxString -> std::string conversion is only available in wxUSE_STL case,
+    // notice that implicit wxString -> std::string conversion is only
-    // because it conflicts with conversion to const char*/wchar_t*:
+    // available in wxUSE_STL case, because it conflicts with conversion to
+    // const char*/wchar_t*
 #if wxUSE_STL
     std::string s5 = s4;
+#else
+    std::string s5 = s4.ToStdString();
+#endif
     CPPUNIT_ASSERT_EQUAL( "hello", s5 );
 
+#if wxUSE_STL
     wxStdWideString s6 = s4;
-    CPPUNIT_ASSERT_EQUAL( "hello", s6 );
+#else
+    wxStdWideString s6 = s4.ToStdWstring();
 #endif
+    CPPUNIT_ASSERT_EQUAL( "hello", s6 );
 
     std::string s7(s4);
     CPPUNIT_ASSERT( s7 == "hello" );