CODEWITHSUNDEEP
c
Angus
Angus

Reputation: 12631

Changing the address of a variable

Is there a way to set an integer variable at the absolute address 0x67a9 to the value 0xaa55? The compiler is a pure ANSI compiler.

How to accomplish this?

This is a program related to embedded systems. As in there we can access a specific memory location.

Upvotes: 4

Views: 23309

Answers (3)

user3015682
user3015682

Reputation: 1255

Depends on how the compiler compiles I would think.

-If when compiling it decodes each instance of a variable to a final address you wouldn't be able to change the address of a regular variable.

-If when compiling it decodes each instance of a variable to reference a spot of a lookup table for its address this might be possible, though you best make sure the address you set it to is allocated.

For example say the 'lookup' address of variable A is 0x1000, and the value found at 0x1000 is 0x2000, so the contents of A is at 0x2000. To change the address of A you simply change the value at 0x1000. Set the value of 0x1000 to 0x3000 and then the contents of A is at 0x3000.

Ya this is how pointers work, but it might be possible that under the hood a compiler might treat them the same (regular variables simply being pointers that are automatically dereferenced.) Of course you could also just make all variables pointers and prepare yourself for a lot of de-referencing in your code.

Upvotes: 0

phoxis
phoxis

Reputation: 61991

int *ptr = (int *) 0x67a9;
*ptr = 0xaa55;  // MBR signature ?

EDIT

You cannot change the address of a variable, you can only point to some address with a pointer, which is shown above.

Upvotes: 7

Bill
Bill

Reputation: 924

Try this:

*((int*)0x67a9) = 0xaa55;

Upvotes: 11

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