I am trying to make a global byte array from a string with:
point := []byte{0x23f32...}
But I am getting the error:
untyped string constant "0x23f32...) as byte value in array or slice literal
I know what I should use a type conversion to convert a string to a slice of bytes, i.e. use of () instead of {}.
point := []byte(0x23f32...)
The code in the question is a composite literal. However, I am using operators as a global variable, so I think that I cannot declare the variable that way. Also, further in the code, logically, I will also have to use [33]byte, so I'm worried about how to declare point []byte here so that I don't have a type error later like "mismatched types [32]byte and []byte".
So keeping these two questions in mind, could you please tell me how to deal with point := []byte here correctly?
CodePudding user response：
0x23f32... is a integer literal and won't convert to a byte (or bytes). You will get this compile-time error for var point = []byte{0x23f32}
cannot use 0x23f32 (untyped int constant 147250) as byte value in array or slice literal (overflows)
Assuming that what you expect to get (it's not clear from your question) from something like
point := []byte{0x23f32 . . . }
is essentially
point := []byte{0x23,0xf3,0x2? . . . }
...
First, if you are trying to declare a "global" variable (e.g. a package-scoped variable), you need to use the var <name> <type> = <value> form. You can't use <name> := <value>.
Second, you can initialize a []byte in a couple different ways:
var p1 []byte = []byte{ 0x12, 0x23, 0x45, . . . }
an array/slice of hex constants, each needs to be in the range 0x00-0xFF (0-255 decimal).var p2 []byte = []byte{ "\x12\x23\x45 . . ." }
a string containing the desired bytes.var p3 []byte = []byte{ 18, 35, 69 . . . }
an array/slice of decimal constantsvar p4 []byte = []byte{ '\x12', '\x23', '\x45' . . . }
an array slice of individual byte literals. Note that if one specifies a value outside the range of a byte (0x00–0xFF, 0-255 decimal), you'll get a compile time error along the lines of:cannot use 'ш' (untyped rune constant 1096) as byte value in array or slice literal (overflows)
Note that the above 4 examples all yield exactly the same value.
CodePudding user response：
If you need to convert 32 bit number to bytes, you can do this:
package main
import (
"encoding/binary"
"fmt"
)
func main() {
var point [4]byte
binary.BigEndian.PutUint32(point[:], 0x23f32)
fmt.Println(point) // [0 2 63 50]
}