Including Q_OBJECT in another macro

[Thuan Seah Tan]

Hi everyone,

I encountered an issue where visual studio complains the class declarations lacks Q_OBJECT macro.

The class definition looked something like this before:

class Abc : QObject
{
    Q_OBJECT
    MY_CUSTOM_MACRO(Abc)
public:
    Abc();
};

class Abc : QObject
{
    Q_OBJECT
    MY_CUSTOM_MACRO(Abc)
public:
    Abc();
};

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Because we use the MY_CUSTOM_MACRO along with Q_OBJECT a lot, I have attempt to refactor the code so Q_OBJECT is now part of the MY_CUSTOM_MACRO. So I have changed definition of MY_CUSTOM_MACRO from this:

#define MY_CUSTOM_MACRO (E) \
public: \
    void* operator new( size_t size ) \
    { \
		void *storage = malloc(size); \
		return storage; \
    } \
private:

#define MY_CUSTOM_MACRO (E) \
public: \
    void* operator new( size_t size ) \
    { \
		void *storage = malloc(size); \
		return storage; \
    } \
private:

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to this:

#define MY_CUSTOM_MACRO (E) \
    Q_OBJECT \
public: \
    void* operator new( size_t size ) \
    { \
		void *storage = malloc(size); \
		return storage; \
    } \
private:

#define MY_CUSTOM_MACRO (E) \
    Q_OBJECT \
public: \
    void* operator new( size_t size ) \
    { \
		void *storage = malloc(size); \
		return storage; \
    } \
private:

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And the declaration of class Abc to this:

class Abc : QObject
{
    MY_CUSTOM_MACRO(Abc)
public:
    Abc();
};

class Abc : QObject
{
    MY_CUSTOM_MACRO(Abc)
public:
    Abc();
};

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This is when the error of missing Q_OBJECT macro starts popping up. Does moc or something scans the header file for Q_OBJECT without expanding MY_CUSTOM_MACRO or something and hence causing the error? Or is it something else I missed?

Thuan

[ChrisW67]

Does moc or something scans the header file for Q_OBJECT without expanding MY_CUSTOM_MACRO or something and hence causing the error?

Got it in one. moc does not include a complete C++ preprocessor or have access to the entire (compiler dependent) source code environment to allow this.