pub trait Cread<Ctx, I = usize>: Index<I> + Index<RangeFrom<I>> where
Ctx: Copy, {
fn cread_with<N: FromCtx<Ctx, <Self as Index<RangeFrom<I>>>::Output>>(
&self,
offset: I,
ctx: Ctx
) -> N { ... }
fn cread<N: FromCtx<Ctx, <Self as Index<RangeFrom<I>>>::Output>>(
&self,
offset: I
) -> N
where
Ctx: Default,
{ ... }
}Expand description
Core-read - core, no_std friendly trait for reading basic traits from byte buffers. Cannot fail unless the buffer is too small, in which case an assert fires and the program panics.
If your type implements FromCtx then you can cread::<YourType>(offset).
Example
use scroll::{ctx, Cread, LE};
#[repr(packed)]
struct Bar {
foo: i32,
bar: u32,
}
impl ctx::FromCtx<scroll::Endian> for Bar {
fn from_ctx(bytes: &[u8], ctx: scroll::Endian) -> Self {
use scroll::Cread;
Bar { foo: bytes.cread_with(0, ctx), bar: bytes.cread_with(4, ctx) }
}
}
let bytes = [0xff, 0xff, 0xff, 0xff, 0xef,0xbe,0xad,0xde,];
let bar = bytes.cread_with::<Bar>(0, LE);
// Remember that you need to copy out fields from packed structs
// with a `{}` block instead of borrowing them directly
// ref: https://github.com/rust-lang/rust/issues/46043
assert_eq!({bar.foo}, -1);
assert_eq!({bar.bar}, 0xdeadbeef);Provided methods
Reads a value from Self at offset with ctx. Cannot fail.
If the buffer is too small for the value requested, this will panic.
Example
use scroll::{Cread, BE, LE};
use std::i64::MAX;
let bytes = [0x7f,0xff,0xff,0xff,0xff,0xff,0xff,0xff, 0xef,0xbe,0xad,0xde,];
let foo = bytes.cread_with::<i64>(0, BE);
let bar = bytes.cread_with::<u32>(8, LE);
assert_eq!(foo, MAX);
assert_eq!(bar, 0xdeadbeef);Reads a value implementing FromCtx from Self at offset,
with the target machine’s endianness.
For the primitive types, this will be the target machine’s endianness.
Example
use scroll::Cread;
let bytes = [0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0xef,0xbe,0x00,0x00,];
let foo = bytes.cread::<i64>(0);
let bar = bytes.cread::<u32>(8);
#[cfg(target_endian = "little")]
assert_eq!(foo, 1);
#[cfg(target_endian = "big")]
assert_eq!(foo, 0x100_0000_0000_0000);
#[cfg(target_endian = "little")]
assert_eq!(bar, 0xbeef);
#[cfg(target_endian = "big")]
assert_eq!(bar, 0xefbe0000);