文件字节数组长度转到

Question

I have recently started to learn Go. To start with I decided that I would write some code to open a file and output its contents on the terminal window. So far I have been writing code like this:

file, err := os.Open("./blah.txt")

data := make([]byte, 100)

count, err := file.Read(data)

To obtain up to 100 bytes from a file. Is there any way to ascertain the byte count on a file, such that you could set the correct (or more sensible) byte array length just using the standard Go library?

I understand you could use a slice with something like Append() once the extremities of the array have been reached, but I just wondered whether the file size/length/whatever could be accessed prior to instantiating an array through file metadata or something similar.

Answer 1

I assume what you need is a way to get file size in bytes to create a slice of the same size:

f, err := f.Stat()
// handle error 
// ...
size := f.Size()

(see FileInfo for more)

You can then use this size to initialise a slice.

data := make([]byte, size)

You can also consider reading the whole file in one call using ioutil.ReadFile.