Trait libc::prelude::fmt::Debug

1.0.0 · source ·

pub trait Debug {
    // Required method
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>;
}

Expand description

? formatting.

Debug should format the output in a programmer-facing, debugging context.

Generally speaking, you should just derive a Debug implementation.

When used with the alternate format specifier #?, the output is pretty-printed.

For more information on formatters, see the module-level documentation.

This trait can be used with #[derive] if all fields implement Debug. When derived for structs, it will use the name of the struct, then {, then a comma-separated list of each field’s name and Debug value, then }. For enums, it will use the name of the variant and, if applicable, (, then the Debug values of the fields, then ).

§Stability

Derived Debug formats are not stable, and so may change with future Rust versions. Additionally, Debug implementations of types provided by the standard library (std, core, alloc, etc.) are not stable, and may also change with future Rust versions.

§Examples

Deriving an implementation:

#[derive(Debug)]
struct Point {
    x: i32,
    y: i32,
}

let origin = Point { x: 0, y: 0 };

assert_eq!(
    format!("The origin is: {origin:?}"),
    "The origin is: Point { x: 0, y: 0 }",
);

Manually implementing:

use std::fmt;

struct Point {
    x: i32,
    y: i32,
}

impl fmt::Debug for Point {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Point")
         .field("x", &self.x)
         .field("y", &self.y)
         .finish()
    }
}

let origin = Point { x: 0, y: 0 };

assert_eq!(
    format!("The origin is: {origin:?}"),
    "The origin is: Point { x: 0, y: 0 }",
);

There are a number of helper methods on the Formatter struct to help you with manual implementations, such as debug_struct.

Types that do not wish to use the standard suite of debug representations provided by the Formatter trait (debug_struct, debug_tuple, debug_list, debug_set, debug_map) can do something totally custom by manually writing an arbitrary representation to the Formatter.

impl fmt::Debug for Point {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "Point [{} {}]", self.x, self.y)
    }
}

Debug implementations using either derive or the debug builder API on Formatter support pretty-printing using the alternate flag: {:#?}.

Pretty-printing with #?:

#[derive(Debug)]
struct Point {
    x: i32,
    y: i32,
}

let origin = Point { x: 0, y: 0 };

let expected = "The origin is: Point {
    x: 0,
    y: 0,
}";
assert_eq!(format!("The origin is: {origin:#?}"), expected);

Required Methods§

1.0.0 · source

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

§Errors

This function should return Err if, and only if, the provided Formatter returns Err. String formatting is considered an infallible operation; this function only returns a Result because writing to the underlying stream might fail and it must provide a way to propagate the fact that an error has occurred back up the stack.

§Examples

use std::fmt;

struct Position {
    longitude: f32,
    latitude: f32,
}

impl fmt::Debug for Position {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_tuple("")
         .field(&self.longitude)
         .field(&self.latitude)
         .finish()
    }
}

let position = Position { longitude: 1.987, latitude: 2.983 };
assert_eq!(format!("{position:?}"), "(1.987, 2.983)");

assert_eq!(format!("{position:#?}"), "(
    1.987,
    2.983,
)");

Implementors§

1.16.0 · source§

Trait libc::prelude::fmt::DebugCopy item path

§Stability

§Examples

Required Methods§

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

§Errors

§Examples

Implementors§

impl Debug for c_void

impl Debug for DIR

impl Debug for FILE

impl Debug for fpos_t

impl Debug for timezone

impl Debug for fpos64_t

impl Debug for tpacket_versions

impl Debug for libc::prelude::fmt::Alignment

impl Debug for AsciiChar

impl Debug for core::cmp::Ordering

impl Debug for Infallible

impl Debug for IpAddr

impl Debug for Ipv6MulticastScope

impl Debug for SocketAddr

impl Debug for FpCategory

impl Debug for IntErrorKind

impl Debug for SearchStep

impl Debug for core::sync::atomic::Ordering

impl Debug for bool

impl Debug for char

impl Debug for f16

impl Debug for f32

impl Debug for f64

impl Debug for f128

impl Debug for i8

impl Debug for i16

impl Debug for i32

impl Debug for i64

impl Debug for i128

impl Debug for isize

impl Debug for !

impl Debug for str

impl Debug for u8

impl Debug for u16

impl Debug for u32

impl Debug for u64

impl Debug for u128

impl Debug for ()

impl Debug for usize

impl Debug for termios2

impl Debug for msqid_ds

impl Debug for semid_ds

impl Debug for sigset_t

impl Debug for sysinfo

impl Debug for statvfs

impl Debug for _libc_fpstate

impl Debug for _libc_fpxreg

impl Debug for _libc_xmmreg

impl Debug for clone_args

impl Debug for flock64

impl Debug for flock

impl Debug for ipc_perm

impl Debug for mcontext_t

impl Debug for pthread_attr_t

impl Debug for ptrace_rseq_configuration

impl Debug for shmid_ds

impl Debug for sigaction

impl Debug for siginfo_t

impl Debug for stack_t

impl Debug for stat64

impl Debug for stat

impl Debug for statfs64

impl Debug for statfs

impl Debug for statvfs64

impl Debug for ucontext_t

impl Debug for user

impl Debug for user_fpregs_struct

impl Debug for user_regs_struct

impl Debug for Elf32_Chdr

impl Debug for Elf64_Chdr

impl Debug for __c_anonymous_ptrace_syscall_info_entry

impl Debug for __c_anonymous_ptrace_syscall_info_exit

Trait libc::prelude::fmt::Debug