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Can a member variable be declared const in a class without initialization?

Note: This was originally posted on 5th January 2010 at http://forums.arm.com

I am trying to define a class providing an interface to hardware registers. Some of the registers are read-only. I would like to declare these registers const so they cannot be written, but the compiler is insisting I initialize them. But by initializing them, it is guranteed they will be written.

Does anyone have a solution to this dilemma?

Thanks.

Sincerely,
Steve.

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zart zurt over 12 years ago

Note: This was originally posted on 6th January 2010 at http://forums.arm.com

Thanks for the input.

The codebase I am working with uses C++ extensively. It uses the linker to locate the object instantiated from the hardware registers class.

Here is an example:

(in registers.h file)
class c_Registers
{
public:
    UINT32 GetRegister3() { return rw_register_3; }
    SetRegister3(UINT32 value) { rw_register_3 = value; }
    UINT32 GetRegister4() { return ro_register_3; }

private:
    UINT32 rw_register_1;
    UINT32 rw_register_2;
    UINT32 rw_register_3;
    UINT32 const ro_register_4;
    UINT32 const ro_register_5;
};

(in registers.cpp file)
#pragma arm section zidata = "REG"
class c_Registers Registers;

(in scatter load file)
HW_REGISTERS_HDSECT 0xA000000 UNINIT
{
    registers.o (REG)
}

What I want to do is be able to declare read only registers, ro_register_4 and ro_register_5, as const to protect against anyone adding code that would write the registers.

Unfortunately, the compiler wants me to initialize the const variables.

Thanks for your help.

Sincerely,
Steve.

IMHO, using pragmas and modifying scatter file is overkill for this.
But if you desperately have to do it this way, just initialize the const variables.
These const variables will be put in place long before you powerup that hardware.

I dont know your particular hardware but there should be no problem. Even if the
hardware block is running, writing to a read-only hardware register should not matter.
That particular hardware should simply ignore that write request, and that is all...
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zart zurt over 12 years ago

Note: This was originally posted on 6th January 2010 at http://forums.arm.com

Thanks for the input.

The codebase I am working with uses C++ extensively. It uses the linker to locate the object instantiated from the hardware registers class.

Here is an example:

(in registers.h file)
class c_Registers
{
public:
    UINT32 GetRegister3() { return rw_register_3; }
    SetRegister3(UINT32 value) { rw_register_3 = value; }
    UINT32 GetRegister4() { return ro_register_3; }

private:
    UINT32 rw_register_1;
    UINT32 rw_register_2;
    UINT32 rw_register_3;
    UINT32 const ro_register_4;
    UINT32 const ro_register_5;
};

(in registers.cpp file)
#pragma arm section zidata = "REG"
class c_Registers Registers;

(in scatter load file)
HW_REGISTERS_HDSECT 0xA000000 UNINIT
{
    registers.o (REG)
}

What I want to do is be able to declare read only registers, ro_register_4 and ro_register_5, as const to protect against anyone adding code that would write the registers.

Unfortunately, the compiler wants me to initialize the const variables.

Thanks for your help.

Sincerely,
Steve.

IMHO, using pragmas and modifying scatter file is overkill for this.
But if you desperately have to do it this way, just initialize the const variables.
These const variables will be put in place long before you powerup that hardware.

I dont know your particular hardware but there should be no problem. Even if the
hardware block is running, writing to a read-only hardware register should not matter.
That particular hardware should simply ignore that write request, and that is all...
Cancel
Vote up 0 Vote down

Cancel

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