Remove needless uses of wxString::c_str() in wxString::Format...

... and similar wx "variadics," which all treat wxString smartly enough that
you don't need this.

Don't need c_str either to convert wxString to const wxChar * because
wxString has a conversion operator that does the same.

src/xml/XMLFileReader.cpp

@@ -43,7 +43,7 @@ bool XMLFileReader::Parse(XMLTagHandler *baseHandler,
 {
    wxFFile theXMLFile(fname, wxT("rb"));
    if (!theXMLFile.IsOpened()) {
-      mErrorStr.Printf(_("Could not open file: \"%s\""), fname.c_str());
+      mErrorStr.Printf(_("Could not open file: \"%s\""), fname);
       return false;
    }
 
@@ -72,7 +72,7 @@ bool XMLFileReader::Parse(XMLTagHandler *baseHandler,
    if (mBaseHandler)
       return true;
    else {
-      mErrorStr.Printf(_("Could not load file: \"%s\""), fname.c_str());
+      mErrorStr.Printf(_("Could not load file: \"%s\""), fname);
       return false;
    }
 }

src/xml/XMLTagHandler.cpp

@@ -194,18 +194,18 @@ bool XMLTagHandler::ReadXMLTag(const char *tag, const char **attrs)
 // added by a cast after creating the array of pointers-to-non-const chars.
    auto out_attrs = std::make_unique<const wxChar *[]>(tmp_attrs.GetCount() + 1);
    for (size_t i=0; i<tmp_attrs.GetCount(); i++) {
-      out_attrs[i] = tmp_attrs[i].c_str();
+      out_attrs[i] = tmp_attrs[i];
    }
    out_attrs[tmp_attrs.GetCount()] = 0;
 
-   bool result = HandleXMLTag(UTF8CTOWX(tag).c_str(), out_attrs.get());
+   bool result = HandleXMLTag(UTF8CTOWX(tag), out_attrs.get());
 
    return result;
 }
 
 void XMLTagHandler::ReadXMLEndTag(const char *tag)
 {
-   HandleXMLEndTag(UTF8CTOWX(tag).c_str());
+   HandleXMLEndTag(UTF8CTOWX(tag));
 }
 
 void XMLTagHandler::ReadXMLContent(const char *s, int len)
@@ -215,5 +215,5 @@ void XMLTagHandler::ReadXMLContent(const char *s, int len)
 
 XMLTagHandler *XMLTagHandler::ReadXMLChild(const char *tag)
 {
-   return HandleXMLChild(UTF8CTOWX(tag).c_str());
+   return HandleXMLChild(UTF8CTOWX(tag));
 }

src/xml/XMLWriter.cpp

@@ -89,7 +89,7 @@ void XMLWriter::StartTag(const wxString &name)
       Write(wxT("\t"));
    }
 
-   Write(wxString::Format(wxT("<%s"), name.c_str()));
+   Write(wxString::Format(wxT("<%s"), name));
 
    mTagstack.Insert(name, 0);
    mHasKids[0] = true;
@@ -113,7 +113,7 @@ void XMLWriter::EndTag(const wxString &name)
                for (i = 0; i < mDepth - 1; i++) {
                   Write(wxT("\t"));
                }
-               Write(wxString::Format(wxT("</%s>\n"), name.c_str()));
+               Write(wxString::Format(wxT("</%s>\n"), name));
             }
          }
          else {
@@ -132,8 +132,8 @@ void XMLWriter::WriteAttr(const wxString &name, const wxString &value)
 // may throw from Write()
 {
    Write(wxString::Format(wxT(" %s=\"%s\""),
-      name.c_str(),
-      XMLEsc(value).c_str()));
+      name,
+      XMLEsc(value)));
 }
 
 void XMLWriter::WriteAttr(const wxString &name, const wxChar *value)
@@ -146,7 +146,7 @@ void XMLWriter::WriteAttr(const wxString &name, int value)
 // may throw from Write()
 {
    Write(wxString::Format(wxT(" %s=\"%d\""),
-      name.c_str(),
+      name,
       value));
 }
 
@@ -154,7 +154,7 @@ void XMLWriter::WriteAttr(const wxString &name, bool value)
 // may throw from Write()
 {
    Write(wxString::Format(wxT(" %s=\"%d\""),
-      name.c_str(),
+      name,
       value));
 }
 
@@ -162,7 +162,7 @@ void XMLWriter::WriteAttr(const wxString &name, long value)
 // may throw from Write()
 {
    Write(wxString::Format(wxT(" %s=\"%ld\""),
-      name.c_str(),
+      name,
       value));
 }
 
@@ -170,7 +170,7 @@ void XMLWriter::WriteAttr(const wxString &name, long long value)
 // may throw from Write()
 {
    Write(wxString::Format(wxT(" %s=\"%lld\""),
-      name.c_str(),
+      name,
       value));
 }
 
@@ -178,7 +178,7 @@ void XMLWriter::WriteAttr(const wxString &name, size_t value)
 // may throw from Write()
 {
    Write(wxString::Format(wxT(" %s=\"%lld\""),
-      name.c_str(),
+      name,
       (long long) value));
 }
 
@@ -186,16 +186,16 @@ void XMLWriter::WriteAttr(const wxString &name, float value, int digits)
 // may throw from Write()
 {
    Write(wxString::Format(wxT(" %s=\"%s\""),
-      name.c_str(),
-      Internat::ToString(value, digits).c_str()));
+      name,
+      Internat::ToString(value, digits)));
 }
 
 void XMLWriter::WriteAttr(const wxString &name, double value, int digits)
 // may throw from Write()
 {
    Write(wxString::Format(wxT(" %s=\"%s\""),
-      name.c_str(),
-      Internat::ToString(value, digits).c_str()));
+      name,
+      Internat::ToString(value, digits)));
 }
 
 void XMLWriter::WriteData(const wxString &value)
@@ -219,7 +219,7 @@ void XMLWriter::WriteSubTree(const wxString &value)
       mHasKids[0] = true;
    }
 
-   Write(value.c_str());
+   Write(value);
 }
 
 // See http://www.w3.org/TR/REC-xml for reference