勾选igore namespace declarations
参数解释如下：
Special Language Options
When you click the Special button in the Preferences: Languages dialog box, the Special Language Options dialog box appears. This dialog box controls special options for built-in languages.
C/C++ Options
Ignore namespace declarations
If checked, then namespace declarations are simply ignored in C++ code. All symbols declared within the namespaces are considered at the file scope, as though you did not write the namespace declaration.
If not checked (the default), then symbols declared within namespaces are considered in the namespace scope.