std::fmt::Formatter - Rust
Description: API documentation for the Rust `Formatter` struct in crate `std`.
Keywords: rust, rustlang, rust-lang, Formatter

# 1.0.0[−][src]Struct std::fmt::Formatter

    pub struct Formatter<'a> where
        'a: 'a,  { /* fields omitted */ }

A struct to represent both where to emit formatting strings to and how they should be formatted. A mutable version of this is passed to all formatting traits.

## Methods

###

`impl<'a> Formatter<'a>`

[src]

####

`pub fn pad_integral( &mut self, is_nonnegative: bool, prefix: &str, buf: &str ) -> Result<(), Error>`

[src]

Performs the correct padding for an integer which has already been emitted into a str. The str should not contain the sign for the integer, that will be added by this method.

# Arguments

- is_nonnegative - whether the original integer was either positive or zero.
- prefix - if the '#' character (Alternate) is provided, this is the prefix to put in front of the number.
- buf - the byte array that the number has been formatted into

This function will correctly account for the flags provided as well as the minimum width. It will not take precision into account.

# Examples

    use std::fmt;

    struct Foo { nb: i32 };

    impl Foo {
        fn new(nb: i32) -> Foo {
            Foo {
                nb,
            }
        }
    }

    impl fmt::Display for Foo {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            // We need to remove "-" from the number output.
            let tmp = self.nb.abs().to_string();

            formatter.pad_integral(self.nb > 0, "Foo ", &tmp)
        }
    }

    assert_eq!(&format!("{}", Foo::new(2)), "2");
    assert_eq!(&format!("{}", Foo::new(-1)), "-1");
    assert_eq!(&format!("{:#}", Foo::new(-1)), "-Foo 1");
    assert_eq!(&format!("{:0>#8}", Foo::new(-1)), "00-Foo 1");Run

####

`pub fn pad(&mut self, s: &str) -> Result<(), Error>`

[src]

This function takes a string slice and emits it to the internal buffer after applying the relevant formatting flags specified. The flags recognized for generic strings are:

- width - the minimum width of what to emit
- fill/align - what to emit and where to emit it if the string provided needs to be padded
- precision - the maximum length to emit, the string is truncated if it is longer than this length

Notably this function ignores the `flag` parameters.

# Examples

    use std::fmt;

    struct Foo;

    impl fmt::Display for Foo {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            formatter.pad("Foo")
        }
    }

    assert_eq!(&format!("{:<4}", Foo), "Foo ");
    assert_eq!(&format!("{:0>4}", Foo), "0Foo");Run

####

`pub fn write_str(&mut self, data: &str) -> Result<(), Error>`

[src]

Writes some data to the underlying buffer contained within this formatter.

# Examples

    use std::fmt;

    struct Foo;

    impl fmt::Display for Foo {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            formatter.write_str("Foo")
            // This is equivalent to:
            // write!(formatter, "Foo")
        }
    }

    assert_eq!(&format!("{}", Foo), "Foo");
    assert_eq!(&format!("{:0>8}", Foo), "Foo");Run

####

`pub fn write_fmt(&mut self, fmt: Arguments) -> Result<(), Error>`

[src]

Writes some formatted information into this instance.

# Examples

    use std::fmt;

    struct Foo(i32);

    impl fmt::Display for Foo {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            formatter.write_fmt(format_args!("Foo {}", self.0))
        }
    }

    assert_eq!(&format!("{}", Foo(-1)), "Foo -1");
    assert_eq!(&format!("{:0>8}", Foo(2)), "Foo 2");Run

####

`pub fn flags(&self) -> u32`

[src]

Deprecated since 1.24.0

: use the `sign_plus`, `sign_minus`, `alternate`, or `sign_aware_zero_pad` methods instead

Flags for formatting

####

`pub fn fill(&self) -> char`

1.5.0
[src]

Character used as 'fill' whenever there is alignment.

# Examples

    use std::fmt;

    struct Foo;

    impl fmt::Display for Foo {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            let c = formatter.fill();
            if let Some(width) = formatter.width() {
                for _ in 0..width {
                    write!(formatter, "{}", c)?;
                }
                Ok(())
            } else {
                write!(formatter, "{}", c)
            }
        }
    }

    // We set alignment to the left with ">".
    assert_eq!(&format!("{:G>3}", Foo), "GGG");
    assert_eq!(&format!("{:t>6}", Foo), "tttttt");Run

####

`pub fn align(&self) -> Option<Alignment>`

1.28.0
[src]

Flag indicating what form of alignment was requested.

# Examples

    extern crate core;

    use std::fmt::{self, Alignment};

    struct Foo;

    impl fmt::Display for Foo {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            let s = if let Some(s) = formatter.align() {
                match s {
                    Alignment::Left    => "left",
                    Alignment::Right   => "right",
                    Alignment::Center  => "center",
                }
            } else {
                "into the void"
            };
            write!(formatter, "{}", s)
        }
    }

    fn main() {
        assert_eq!(&format!("{:<}", Foo), "left");
        assert_eq!(&format!("{:>}", Foo), "right");
        assert_eq!(&format!("{:^}", Foo), "center");
        assert_eq!(&format!("{}", Foo), "into the void");
    }Run

####

`pub fn width(&self) -> Option<usize>`

1.5.0
[src]

Optionally specified integer width that the output should be.

# Examples

    use std::fmt;

    struct Foo(i32);

    impl fmt::Display for Foo {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            if let Some(width) = formatter.width() {
                // If we received a width, we use it
                write!(formatter, "{:width$}", &format!("Foo({})", self.0), width = width)
            } else {
                // Otherwise we do nothing special
                write!(formatter, "Foo({})", self.0)
            }
        }
    }

    assert_eq!(&format!("{:10}", Foo(23)), "Foo(23)   ");
    assert_eq!(&format!("{}", Foo(23)), "Foo(23)");Run

####

`pub fn precision(&self) -> Option<usize>`

1.5.0
[src]

Optionally specified precision for numeric types.

# Examples

    use std::fmt;

    struct Foo(f32);

    impl fmt::Display for Foo {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            if let Some(precision) = formatter.precision() {
                // If we received a precision, we use it.
                write!(formatter, "Foo({1:.*})", precision, self.0)
            } else {
                // Otherwise we default to 2.
                write!(formatter, "Foo({:.2})", self.0)
            }
        }
    }

    assert_eq!(&format!("{:.4}", Foo(23.2)), "Foo(23.2000)");
    assert_eq!(&format!("{}", Foo(23.2)), "Foo(23.20)");Run

####

`pub fn sign_plus(&self) -> bool`

1.5.0
[src]

Determines if the `+` flag was specified.

# Examples

    use std::fmt;

    struct Foo(i32);

    impl fmt::Display for Foo {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            if formatter.sign_plus() {
                write!(formatter,
                       "Foo({}{})",
                       if self.0 < 0 { '-' } else { '+' },
                       self.0)
            } else {
                write!(formatter, "Foo({})", self.0)
            }
        }
    }

    assert_eq!(&format!("{:+}", Foo(23)), "Foo(+23)");
    assert_eq!(&format!("{}", Foo(23)), "Foo(23)");Run

####

`pub fn sign_minus(&self) -> bool`

1.5.0
[src]

Determines if the `-` flag was specified.

# Examples

    use std::fmt;

    struct Foo(i32);

    impl fmt::Display for Foo {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            if formatter.sign_minus() {
                // You want a minus sign? Have one!
                write!(formatter, "-Foo({})", self.0)
            } else {
                write!(formatter, "Foo({})", self.0)
            }
        }
    }

    assert_eq!(&format!("{:-}", Foo(23)), "-Foo(23)");
    assert_eq!(&format!("{}", Foo(23)), "Foo(23)");Run

####

`pub fn alternate(&self) -> bool`

1.5.0
[src]

Determines if the `#` flag was specified.

# Examples

    use std::fmt;

    struct Foo(i32);

    impl fmt::Display for Foo {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            if formatter.alternate() {
                write!(formatter, "Foo({})", self.0)
            } else {
                write!(formatter, "{}", self.0)
            }
        }
    }

    assert_eq!(&format!("{:#}", Foo(23)), "Foo(23)");
    assert_eq!(&format!("{}", Foo(23)), "23");Run

####

`pub fn sign_aware_zero_pad(&self) -> bool`

1.5.0
[src]

Determines if the `0` flag was specified.

# Examples

    use std::fmt;

    struct Foo(i32);

    impl fmt::Display for Foo {
        fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            assert!(formatter.sign_aware_zero_pad());
            assert_eq!(formatter.width(), Some(4));
            // We ignore the formatter's options.
            write!(formatter, "{}", self.0)
        }
    }

    assert_eq!(&format!("{:04}", Foo(23)), "23");Run

####

`pub fn debug_struct(&'b mut self, name: &str) -> DebugStruct<'b, 'a>`

1.2.0
[src]

Creates a `DebugStruct` builder designed to assist with creation of `fmt::Debug` implementations for structs.

# Examples

    use std::fmt;
    use std::net::Ipv4Addr;

    struct Foo {
        bar: i32,
        baz: String,
        addr: Ipv4Addr,
    }

    impl fmt::Debug for Foo {
        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
            fmt.debug_struct("Foo")
                .field("bar", &self.bar)
                .field("baz", &self.baz)
                .field("addr", &format_args!("{}", self.addr))
                .finish()
        }
    }

    assert_eq!(
        "Foo { bar: 10, baz: \"Hello World\", addr: 127.0.0.1 }",
        format!("{:?}", Foo {
            bar: 10,
            baz: "Hello World".to_string(),
            addr: Ipv4Addr::new(127, 0, 0, 1),
        })
    );Run

####

`pub fn debug_tuple(&'b mut self, name: &str) -> DebugTuple<'b, 'a>`

1.2.0
[src]

Creates a `DebugTuple` builder designed to assist with creation of `fmt::Debug` implementations for tuple structs.

# Examples

    use std::fmt;
    use std::marker::PhantomData;

    struct Foo<T>(i32, String, PhantomData<T>);

    impl<T> fmt::Debug for Foo<T> {
        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
            fmt.debug_tuple("Foo")
                .field(&self.0)
                .field(&self.1)
                .field(&format_args!("_"))
                .finish()
        }
    }

    assert_eq!(
        "Foo(10, \"Hello\", _)",
        format!("{:?}", Foo(10, "Hello".to_string(), PhantomData::<u8>))
    );Run

####

`pub fn debug_list(&'b mut self) -> DebugList<'b, 'a>`

1.2.0
[src]

Creates a `DebugList` builder designed to assist with creation of `fmt::Debug` implementations for list-like structures.

# Examples

    use std::fmt;

    struct Foo(Vec<i32>);

    impl fmt::Debug for Foo {
        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
            fmt.debug_list().entries(self.0.iter()).finish()
        }
    }

    // prints "[10, 11]"
    println!("{:?}", Foo(vec![10, 11]));Run

####

`pub fn debug_set(&'b mut self) -> DebugSet<'b, 'a>`

1.2.0
[src]

Creates a `DebugSet` builder designed to assist with creation of `fmt::Debug` implementations for set-like structures.

# Examples

    use std::fmt;

    struct Foo(Vec<i32>);

    impl fmt::Debug for Foo {
        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
            fmt.debug_set().entries(self.0.iter()).finish()
        }
    }

    // prints "{10, 11}"
    println!("{:?}", Foo(vec![10, 11]));Run

In this more complex example, we use `format_args!` and `.debug_set()` to build a list of match arms:

    use std::fmt;

    struct Arm<'a, L: 'a, R: 'a>(&'a (L, R));
    struct Table<'a, K: 'a, V: 'a>(&'a [(K, V)], V);

    impl<'a, L, R> fmt::Debug for Arm<'a, L, R>
    where
        L: 'a + fmt::Debug, R: 'a + fmt::Debug
    {
        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
            L::fmt(&(self.0).0, fmt)?;
            fmt.write_str(" => ")?;
            R::fmt(&(self.0).1, fmt)
        }
    }

    impl<'a, K, V> fmt::Debug for Table<'a, K, V>
    where
        K: 'a + fmt::Debug, V: 'a + fmt::Debug
    {
        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
            fmt.debug_set()
            .entries(self.0.iter().map(Arm))
            .entry(&Arm(&(format_args!("_"), &self.1)))
            .finish()
        }
    }Run

####

`pub fn debug_map(&'b mut self) -> DebugMap<'b, 'a>`

1.2.0
[src]

Creates a `DebugMap` builder designed to assist with creation of `fmt::Debug` implementations for map-like structures.

# Examples

    use std::fmt;

    struct Foo(Vec<(String, i32)>);

    impl fmt::Debug for Foo {
        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
            fmt.debug_map().entries(self.0.iter().map(|&(ref k, ref v)| (k, v))).finish()
        }
    }

    // prints "{"A": 10, "B": 11}"
    println!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)]));Run

## Trait Implementations

###

`impl<'a> Write for Formatter<'a>`

1.2.0
[src]

####

`fn write_str(&mut self, s: &str) -> Result<(), Error>`

[src]

Writes a slice of bytes into this writer, returning whether the write succeeded. Read more

####

`fn write_char(&mut self, c: char) -> Result<(), Error>`

[src]

Writes a [`char`] into this writer, returning whether the write succeeded. Read more

####

`fn write_fmt(&mut self, args: Arguments) -> Result<(), Error>`

[src]

Glue for usage of the [`write!`] macro with implementors of this trait. Read more

## Auto Trait Implementations

###

`impl<'a> !Send for Formatter<'a>`

###

`impl<'a> !Sync for Formatter<'a>`

## Blanket Implementations

###

`impl<T, U> TryFrom for T where T: From<U>,`

[src]

#### `type Error = !`

🔬 This is a nightly-only experimental API. (`try_from` #33417)

The type returned in the event of a conversion error.

####

`fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>`

[src]

🔬 This is a nightly-only experimental API. (`try_from` #33417)

Performs the conversion.

###

`impl<T> From for T`

[src]

####

`fn from(t: T) -> T`

[src]

Performs the conversion.

###

`impl<T, U> TryInto for T where U: TryFrom<T>,`

[src]

#### `type Error = <U as TryFrom<T>>::Error`

🔬 This is a nightly-only experimental API. (`try_from` #33417)

The type returned in the event of a conversion error.

####

`fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>`

[src]

🔬 This is a nightly-only experimental API. (`try_from` #33417)

Performs the conversion.

###

`impl<T, U> Into for T where U: From<T>,`

[src]

####

`fn into(self) -> U`

[src]

Performs the conversion.

###

`impl<T> Borrow for T where T: ?Sized,`

[src]

####
ⓘImportant traits for &'a mut I

### Important traits for &'a mut I

`impl<'a, I> Iterator for &'a mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W`

`fn borrow(&self) -> &T`

[src]

Immutably borrows from an owned value. Read more

###

`impl<T> BorrowMut for T where T: ?Sized,`

[src]

####
ⓘImportant traits for &'a mut I

### Important traits for &'a mut I

`impl<'a, I> Iterator for &'a mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W`

`fn borrow_mut(&mut self) -> &mut T`

[src]

Mutably borrows from an owned value. Read more

###

`impl<T> Any for T where T: 'static + ?Sized,`

[src]

####

`fn get_type_id(&self) -> TypeId`

[src]

🔬 This is a nightly-only experimental API. (`get_type_id` #27745)

this method will likely be replaced by an associated static

Gets the `TypeId` of `self`. Read more

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