what the -> operand does?

[maremmacinghiala]

Hello C++ experts!

I've a question about the -> operand that I now see quite often in some code for embedded systems. it looks to me to be anotehr way to access the fields of a given structure, but why using this operator istead of using the "." which I was teached from school? is there any difference?

 // for example I have this function :
static void configure_systick_handler(void)
{
	SysTick->CTRL = 0;
	SysTick->LOAD = 999;
	SysTick->VAL  = 0;

}

where SysTick is a strucure of SysTick_Type 

typedef struct
{
  __IO uint32_t CTRL;                    /*!< Offset: 0x000 (R/W)  SysTick Control and Status Register */
  __IO uint32_t LOAD;                    /*!< Offset: 0x004 (R/W)  SysTick Reload Value Register       */
  __IO uint32_t VAL;                     /*!< Offset: 0x008 (R/W)  SysTick Current Value Register      */
  __I  uint32_t CALIB;                   /*!< Offset: 0x00C (R/ )  SysTick Calibration Register        */
} SysTick_Type;


 Put the code you need help with here.

[ResidentBiscuit]

You use the -> when you have a pointer, a '.' when you have an actual object.

//This
ptr->member = 0;
//Is just shorthand for
(*ptr).member = 0;

This is necessary because a pointer itself is nothing other than an address. You have to dereference the pointer to grab the object it points to before you can start accessing members and methods.

[MikeyBoy]

In addition to what ResidentBiscuit said, -> is an operator, not an operand.

In ptr->member, ptr and member are operands, and -> is the operator.

[yulingo]

Given something like:

struct D
{
    int first;
    int second;
}

D* ptrToD;

// These are equivalent
ptrToD->first;
(*D).first;

[maremmacinghiala]

Hello Guys!

Thanks a lot for the clarifications!
Could you also point me some manuals/tutorials that explain such concepts?

it's quite weird that I do not really rember to have studied the usage of -> in my c++ book of ten years ago (...or so!)

BR

[ResidentBiscuit]

Could you also point me some manuals/tutorials that explain such concepts?

What concepts? Points are explained on this site's tutorials. http://www.cplusplus.com/doc/tutorial/pointers/