Function forge_write_start 

pub fn forge_write_start(_fix_version: &str) -> usize

Get the starting position for writing MsgType value for FIX 4.x versions. All FIX 4.x versions have the same header length, so this returns the constant.

Example

let start_pos = forge_write_start("FIX.4.4");
assert_eq!(start_pos, 20);

let start_pos = forge_write_start("FIX.4.2");
assert_eq!(start_pos, 20);