Thank you John Graham.

I solved the second problem easily with your solution.

But, I still having problem with the first problem.
I search through the usr/include directory and also usr/local/include directory and I cannot find any header file of name memory.h.
Anyway, I still rename the header file to become BRBmemory.h and compile again. I still get the same error message.

I also tried to substitute it with other defined constant in the BRBmemory.h. It still giving the same error.

Okay - first things to check:

1) Is BRBmemory.h #included in ProjectApplication.h?

2) If so, could you please post the complete output of trying to compile it?

No.

The included header file in ProjectApplication.h are
ProjectFunctionLayer.h
QLibrary

In ProjectFunctionLayer.h, the included header files are
QString
BRBmemory.h

TeamProtocol.h
.
.
.

Using these, the compiler cannot find the NUM defined in BRBmemory.h that is memory.h previously.

I get information on the net that when a value is defined, it is only available in the file that defined it and the file that include the file that defined it. Is this means NUM is only available in BRBmemory.h and ProjectFunctionLayer.h but not ProjectApplication.h?

Isn't my ProjectApplication.h can read the NUM as it included ProjectFunctionLayer.h which includes BRBmemory.h that have the definition of NUM?

I tried to add option -Dthedefine=its_value and pass to gcc. It works.
Or I have to manually include BRBmemory.h in ProjectApplication.h itself to eliminate that error.
But I wish not to modify the code been provided.

No, that's completely wrong - if you're sure that:

1) ProjectApplication.h #include's ProjectFunctionLayer.h, and

2) ProjectFunctionLayer.h #include's BRBmemory.h

then you *should* have access to things defined in BRBmemory.h from source files that #include ProjectApplication.h.

My first suspicion is that you're using include-guards, and two of your files have the same one. This would mean that when you try and include the second one, it thinks it's already been included, so just skips to the end of the file, leaving you with nothing from that file.

So, check your include-guards and make sure they define something different (e.g. one defines PROJECT_FUNCTION_LAYER_H and the other BRB_MEMORY_H).

Yes, I found include guard in the file, but it includes itself. This means

In ProjectApplication.h,
#ifndef __PROJECTAPPLICATION__
#define __PROJECTAPPLICATION__

#include <ProjectFunctionLayer.h>

#endif

In ProjectFunctionLayer.h,
#ifndef __PROJECTFUNCTIONLAYER__
#define __PROJECTFUNCTIONLAYER__

#include <BRBmemory.h>

#endif