I'm trying to convert an uint32 to a byte array (4 bytes) in Go using the unsafe library:
h := (uint32)(((fh.year*100+fh.month)*100+fh.day)*100 + fh.h)
a := make([]byte, unsafe.Sizeof(h))
copy(a, *(*[]byte)(unsafe.Pointer(&h)))
The first two lines are correct, but then I get a runtime error ( unexpected fault address ) at the copy call.
The next step would be to call Write
_, err = fi.Write(a)
to write the 4 bytes into a file.
I've found other questions with a similar topic, but none with a working code. I'm also aware that unsafe is unsafe.
Any help would be greatly appreciated.
You can convert Golang “type []string” to string using string. Join() function, which takes two parameters. It returns a string.
A uint8 is an unsigned integer, and can only have a positive value of 0 to 255. The ranges are based on the bit size. For binary data, 8 bits can represent a total of 256 different values.
Avoid the unsafe package.
Use the encoding/binary package to convert a uint32
to a slice of bytes:
h := (uint32)(((fh.year*100+fh.month)*100+fh.day)*100 + fh.h)
a := make([]byte, 4)
binary.LittleEndian.PutUint32(a, h)
_, err = fi.Write(a)
This one-liner does the same thing, but has an additional runtime cost:
err := binary.Write(fi, binary.LittleEndian, (uint32)(((fh.year*100+fh.month)*100+fh.day)*100 + fh.h))
Here's how to do the conversion with the unsafe package:
h := (uint32)(((fh.year*100+fh.month)*100+fh.day)*100 + fh.h)
a := (*[4]byte)(unsafe.Pointer(&h))[:]
_, err = fi.Write(a)
The expression (*[4]byte)(unsafe.Pointer(&h))
converts a uint32
pointer to a [4]byte
pointer. The [:]
at the end creates a slice on the [4]byte
.
The code in the question interprets the uint32
as a slice header. The resulting slice is not valid and copy
faults.
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