英文:
golang: convert uint32 (or any built-in type) to []byte (to be written in a file)
问题
我正在尝试使用Go语言中的unsafe库将_uint32_转换为字节数组(4个字节):
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)))
前两行是正确的,但是在_copy_调用处出现了运行时错误(unexpected fault address)。
下一步是调用_Write_函数将这4个字节写入文件:
_, err = fi.Write(a)
我找到了其他类似主题的问题,但没有一个有可用的代码。
我也知道unsafe是不安全的。
非常感谢任何帮助。
英文:
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.
答案1
得分: 20
避免使用unsafe包。
使用encoding/binary包将uint32
转换为字节切片:
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)
这个一行代码也可以实现相同的功能,但会增加额外的运行时开销:
err := binary.Write(fi, binary.LittleEndian, (uint32)(((fh.year*100+fh.month)*100+fh.day)*100 + fh.h))
以下是使用unsafe包进行转换的方法:
h := (uint32)(((fh.year*100+fh.month)*100+fh.day)*100 + fh.h)
a := (*[4]byte)(unsafe.Pointer(&h))[:]
_, err = fi.Write(a)
表达式(*[4]byte)(unsafe.Pointer(&h))
将uint32
指针转换为[4]byte
指针。末尾的[:]
创建了一个[4]byte
的切片。
问题中的代码将uint32
解释为slice header。生成的切片是无效的,copy
操作会出错。
英文:
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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