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- how slice array in rust? 4 answers
i have structure fixed-sized arrays:
struct publicheaderblock_las14 { file_signature: [u8; 4], file_source_id: u16, global_encoding: u16, project_id_data_1: u32, project_id_data_2: u16, project_id_data_3: u16, project_id_data_4: [u8; 8], version_major: u8, version_minor: u8, systemidentifier: [u8; 32], // ... } i'm reading in bytes file fixed size array , copying bytes struct bit bit.
fn create_header_struct_las14(&self, buff: &[u8; 373]) -> publicheaderblock_las14 { publicheaderblock_las14 { file_signature: [buff[0], buff[1], buff[2], buff[3]], file_source_id: (buff[4] | buff[5] << 7) u16, global_encoding: (buff[6] | buff[7] << 7) u16, project_id_data_1: (buff[8] | buff[9] << 7 | buff[10] << 7 | buff[11] << 7) u32, project_id_data_2: (buff[12] | buff[13] << 7) u16, project_id_data_3: (buff[14] | buff[15] << 7) u16, project_id_data_4: [buff[16], buff[17], buff[18], buff[19], buff[20], buff[21], buff[22], buff[23]], version_major: buff[24], version_minor: buff[25], systemidentifier: buff[26..58] } } the last line (systemidentifier) doesn't work, because in struct [u8; 32] , buff[26..58] slice. can return convert slice fixed sized array on range, instead of doing i've done file_signature?
there no safe way initialize array in struct slice. need either resort unsafe block operates directly on uninitialized memory, or use 1 of following 2 initialize-then-mutate strategies:
construct desired array, use initialize struct.
struct foo { arr: [u8; 32], } fn fill(s: &[u8; 373]) -> foo { let mut a: [u8; 32] = default::default(); a.copy_from_slice(&s[26..58]); foo { arr: } } or initialize struct, mutate array inside struct.
#[derive(default)] struct foo { arr: [u8; 32], } fn fill(s: &[u8; 373]) -> foo { let mut f: foo = default::default(); f.arr.copy_from_slice(&s[26..58]); f } the first 1 cleaner if struct has many members. second 1 may little faster if compiler cannot optimize out intermediate copy. use unsafe method if performance bottleneck of program.
