如何使用指针处理存储在变量中的地址？

Question

I need to help how to handle this situation. Variable DestinationAddress which contains start value of memory. And I want to use pointer to write to the address the data. Is it OK?

Example:

long Data32;
long DestinationAddress;
long *temp;

Data32 = 0x00112233;
DestinationAddress = 0x00280000;
temp = DestinationAddress;
*temp = Data32;

Answer 1

When your variables are declared as:

long Data32;
long DestinationAddress;
long *temp;

You may not use

temp = DestinationAddress;

You may use:

temp = &DestinationAddress;

Then, using:

*temp = Data32;

is a valid way to set the value of DestinationAddress to Data32 .

However, the name DestinationAddress and the type used to declare it, long , don't seem to match. If you want DestinationAddress to store an address of a long , it needs to be declared as:

long* DestinationAddress;

If you want to use an integral type instead of a long* to store an address, the types to use are intptr_t or uintptr_t .

uintptr_t Data32;
uintptr_t DestinationAddress;
uintptr_t* temp;

Data32 = 0x00112233;
DestinationAddress = 0x00280000;
temp = &DestinationAddress;
*temp = Data32;

Update, in response to OP's comment

You need to use:

long Data32;
uintptr_t DestinationAddress;
long* temp;

Data32 = 0x00112233;
DestinationAddress = 0x00280000;
temp = (long*)DestinationAddress;
*temp = Data32;

Answer 2

In embedded systems, many hardware registers are located at specific addresses. The software needs to write to and read from these addresses.

The classic (C style) idiom is:

#define USB_STATUS_REGISTER ((uint16_t *) (0x40008250))
uint16_t const * const p_status_register = USB_STATUS_REGISTER;
uint16_t status = *p_status_register;

Answer 3

It's fine as long as 0x00280000 is a valid address - but you should really consider using uintptr_t for storing pointer values if available (instead of long in your example).

But DestinationAddress is an integer. So, you'd need to convert it with a case (otherwise, a compiler might warn about it):

temp = (long*)DestinationAddress;
*temp = Data32;