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Create an object at a given address: Difference between revisions
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</lang>
Some architectures may require special fetch and store operators to access ports. For example, [[Open Firmware]] defines l@ and l! for safe 32-bit port writes.
=={{header|Go}}==
Go has several ways to access arbitrary memory locations using the built-in unsafe package. Since Go doesn't have pointer arithmetic, if the desired memory contains an array, a slice should be used instead of a pointer. The following solution shows both methods.
<lang go>package main
import(
"fmt"
"unsafe"
"reflect"
)
func pointer() {
fmt.Printf("Pointer:\n")
// Create a *int and store the address of 'i' in it. To create a pointer to
// an arbitrary memory location, use something like the following:
// p := (*int)(unsafe.Pointer(uintptr(0x100)))
// And replace '0x100' with the desired address.
var i int
p := &i
fmt.Printf("Before:\n\t%v: %v, %v\n", p, *p, i)
*p = 3
fmt.Printf("After:\n\t%v: %v, %v\n", p, *p, i)
}
func slice() {
fmt.Printf("Slice:\n")
var a [10]byte
// reflect.SliceHeader is a runtime representation of the internal workings
// of a slice. To make it point to a specific address, use something like
// the following:
// h.Data = uintptr(0x100)
// And replace '0x100' with the desired address.
var h reflect.SliceHeader
h.Data = uintptr(unsafe.Pointer(&a)) // The address of the first element of the underlying array.
h.Len = len(a)
h.Cap = len(a)
// Create an actual slice from the SliceHeader.
s := *(*[]byte)(unsafe.Pointer(&h))
fmt.Printf("Before:\n\ts: %v\n\ta: %v\n", s, a)
// Copy a string into the slice. This fills the underlying array, which in
// this case has been manually set to 'a'.
copy(s, "A string.")
fmt.Printf("After:\n\ts: %v\n\ta: %v\n", s, a)
}
func main() {
pointer()
fmt.Println()
slice()
}</lang>
=={{header|PicoLisp}}==
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