Subtracting a macro from a pointer

This is a discussion on Subtracting a macro from a pointer within the C Programming forums, part of the General Programming Boards category; Hi all, I am trying to subtract the value of a macro from a pointer but after this operation, I ...

  1. #1
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    Subtracting a macro from a pointer

    Hi all,

    I am trying to subtract the value of a macro from a pointer but after this operation, I still get the same pointer address.

    In particular, why the following code

    Code:
    	struct list_head *init_tasks = tasks;
    	printk("init_task next task is: 0x%X\n", init_tasks->next);
    gives the same result with this?:

    Code:
    	init_tasks = (uint8_t*)(init_tasks->next - (uint32_t)SEGMENT_OFFSET);
    	printk("init_task next task (phys) is: 0x%X\n", init_tasks);
    Could anyone let me know what I am doing wrong?

    Thanks in advance.

  2. #2
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    What is the definition of SEGMENT_OFFSET ?

    Also which compiler and OS is this for?

  3. #3
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    What is tasks??
    Basically tasks->next = (uint8_t*)(init_tasks->next - (uint32_t)SEGMENT_OFFSET)
    Are you implying this?
    Not enough code. WTF is value of init_tasks for 2nd code segment.

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