arraysdata-conversionvlangbinary-string

Vlang - convert int, u32, u64, f32, f64, etc. to array of bytes in LittleEndian format


I have various variables of different numeric datatypes(int,u32,u64,f32,f64, etc) and want to convert them to an array of bytes.

For example:

a := 120  // int datatype
a_bytes = some_function(a)  // What to do here?

println(a_bytes)
// [ x, `\0`, `\0`, `\0`]   should be the output in little endian format
// OR b'x\x00\x00\x00' as a binary string

In python, it can be done as shown in these posts: here and here


Solution

  • This can be done using encoding.binary as mentioned by @Adam Oates in the comments.

    The following example is for 64-bit data. Similar functions are available for 32-bit and big-endian also.

    To convert f64 to/from bytes(u8) we can use math.f64_bits and math.f64_from_bits which converts the float to IEEE 754 binary representation(u64) which is later converted into bytes.

    import encoding.binary
    import math
    
    fn convert_u64_to_bytes(u u64) []u8 {
        mut b := []u8{len: 8, init: 0}
        binary.little_endian_put_u64(mut b, u)
        return b
    }
    
    fn convert_f64_to_bytes(val f64) []u8 {
        u := math.f64_bits(val) // returns IEEE 754 binary representation of f64
        return convert_u64_to_bytes(u)
    }
    
    fn convert_bytes_to_u64(b []u8) u64 {
        return binary.little_endian_u64(b)
    }
    
    fn convert_bytes_to_f64(b []u8) f64 {
        u := binary.little_endian_u64(b)
        return math.f64_from_bits(u)
    }
    
    fn main(){
        i := i64(-120)
        u := u64(1234)
        f := f64(-1235.345)
        
        bi := convert_u64_to_bytes(u64(i))
        bu := convert_u64_to_bytes(u)
        bf := convert_f64_to_bytes(f)
        println('$bi\n$bu\n$bf')
        
        i1 := i64(convert_bytes_to_u64(bi))
        u1 := convert_bytes_to_u64(bu)
        f1 := convert_bytes_to_f64(bf)
        println('$i1\n$u1\n$f1')
    }
    /* OUTPUT
    [0x88, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff]
    [0xd2, 0x04, `\0`, `\0`, `\0`, `\0`, `\0`, `\0`]
    [{, 0x14, 0xae, G, a, M, 0x93, 0xc0]
    -120
    1234
    -1235.345
    */
    

    At the time of writing this article, V is yet to get a proper release. So the syntax, functions, etc. are subject to changes.