Defining a Union at a perticular address in C

[nrmlguru]

Hello,

Please help me to define a Union at particular address.

say at address 0x1234

 

[horace1]

you declare the union, define a pointer to the type and initialise it with the address

typedef	union
{
	unsigned long int value;
	char xch[2];
} TempData;

TempData *ptr= (TempData* )0x1234;

what happens if you use the pointer to access the object pointed to depends on the system you are using and if the pointer holds a valid address, e.g.

ptr->value=1;

if the pointer does not hold a valid address you could get an exception, address error, segmentation error, etc or it may appear to work corrupting memory contents and possibly causing a crash later.