抽象类/函数的编译错误

Question

我在C++抽象类（其他类需要继承和实例化）上遇到了一个奇怪的错误（缺少"；"、无法识别字符串类等）。此外，我希望派生类被强制实现抽象类方法——因此纯virtual=0。

下面是我的抽象类定义。

可绘制.h:

#ifndef __myns__managers__Drawable_h__
#define __myns__managers__Drawable_h__
#include <string>
namespace myns
{
    namespace managers
    {
        class Drawable;
    }
}
namespace myns
{
    namespace managers
    {
        class Drawable
        {
            public:
                virtual float getX() = 0;
                virtual float getY() = 0;
                virtual string getImageFilePath() = 0;
            protected:
                int drawableId;
        };
    }
}
#endif

根据我对C++的相对了解，我想一切都可以，对吧？但当我在VS2010上编译时，它会给我一堆编译错误，如下所示。

我该如何解决这个问题？提前谢谢。

VS构建输出：

1>------ Build started: Project: InteractiveMembranes_vc10, Configuration: X86 Debug Win32 ------
1>  OutputManager.cpp
1>(project dir)managersdrawable.h(23): error C2146: syntax error : missing ';' before identifier 'getImageFilePath'
1>(project dir)managersdrawable.h(23): error C2433: 'interactivemembranes::managers::Drawable::string' : 'virtual' not permitted on data declarations
1>(project dir)managersdrawable.h(23): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>(project dir)managersdrawable.h(23): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>(project dir)managersdrawable.h(23): warning C4183: 'getImageFilePath': missing return type; assumed to be a member function returning 'int'
1>(project dir)managersdrawable.h(23): error C2253: 'interactivemembranes::managers::Drawable::getImageFilePath' : pure specifier or abstract override specifier only allowed on virtual function
1>  Application.cpp
1>(project dir)managersdrawable.h(23): error C2146: syntax error : missing ';' before identifier 'getImageFilePath'
1>(project dir)managersdrawable.h(23): error C2433: 'interactivemembranes::managers::Drawable::string' : 'virtual' not permitted on data declarations
1>(project dir)managersdrawable.h(23): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>(project dir)managersdrawable.h(23): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>(project dir)managersdrawable.h(23): warning C4183: 'getImageFilePath': missing return type; assumed to be a member function returning 'int'
1>(project dir)managersdrawable.h(23): error C2253: 'interactivemembranes::managers::Drawable::getImageFilePath' : pure specifier or abstract override specifier only allowed on virtual function
1>  Generating Code...
1>  Compiling...
1>  TestPersistence.cpp
1>  Generating Code...
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Answer 1

您需要符合string:

virtual std::string getImageFilePath() = 0;

string在std命名空间中，而不是在全局命名空间中。还有using namespace std;选项，它将把名称空间导入全局名称空间，但不要这样做，尤其是在头中。我只是将其作为一种选择，但您应该始终更喜欢限定名称。

编辑：正如Als所指出的，您只能导入您需要的内容：using std::string;。不过，我还是喜欢限定这个名字。