1 // Copyright 2013-2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Utilities for formatting and printing strings.
13 #![stable(feature = "rust1", since = "1.0.0")]
17 use cell::{UnsafeCell, Cell, RefCell, Ref, RefMut, BorrowState};
18 use marker::PhantomData;
26 #[unstable(feature = "fmt_flags_align", issue = "27726")]
27 /// Possible alignments returned by `Formatter::align`
30 /// Indication that contents should be left-aligned.
32 /// Indication that contents should be right-aligned.
34 /// Indication that contents should be center-aligned.
36 /// No alignment was requested.
40 #[stable(feature = "debug_builders", since = "1.2.0")]
41 pub use self::builders::{DebugStruct, DebugTuple, DebugSet, DebugList, DebugMap};
46 #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
53 #[stable(feature = "rust1", since = "1.0.0")]
54 /// The type returned by formatter methods.
55 pub type Result = result::Result<(), Error>;
57 /// The error type which is returned from formatting a message into a stream.
59 /// This type does not support transmission of an error other than that an error
60 /// occurred. Any extra information must be arranged to be transmitted through
62 #[stable(feature = "rust1", since = "1.0.0")]
63 #[derive(Copy, Clone, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
66 /// A collection of methods that are required to format a message into a stream.
68 /// This trait is the type which this modules requires when formatting
69 /// information. This is similar to the standard library's `io::Write` trait,
70 /// but it is only intended for use in libcore.
72 /// This trait should generally not be implemented by consumers of the standard
73 /// library. The `write!` macro accepts an instance of `io::Write`, and the
74 /// `io::Write` trait is favored over implementing this trait.
75 #[stable(feature = "rust1", since = "1.0.0")]
77 /// Writes a slice of bytes into this writer, returning whether the write
80 /// This method can only succeed if the entire byte slice was successfully
81 /// written, and this method will not return until all data has been
82 /// written or an error occurs.
86 /// This function will return an instance of `Error` on error.
87 #[stable(feature = "rust1", since = "1.0.0")]
88 fn write_str(&mut self, s: &str) -> Result;
90 /// Writes a `char` into this writer, returning whether the write succeeded.
92 /// A single `char` may be encoded as more than one byte.
93 /// This method can only succeed if the entire byte sequence was successfully
94 /// written, and this method will not return until all data has been
95 /// written or an error occurs.
99 /// This function will return an instance of `Error` on error.
100 #[stable(feature = "fmt_write_char", since = "1.1.0")]
101 fn write_char(&mut self, c: char) -> Result {
102 self.write_str(unsafe {
103 str::from_utf8_unchecked(c.encode_utf8().as_slice())
107 /// Glue for usage of the `write!` macro with implementors of this trait.
109 /// This method should generally not be invoked manually, but rather through
110 /// the `write!` macro itself.
111 #[stable(feature = "rust1", since = "1.0.0")]
112 fn write_fmt(&mut self, args: Arguments) -> Result {
113 // This Adapter is needed to allow `self` (of type `&mut
114 // Self`) to be cast to a Write (below) without
115 // requiring a `Sized` bound.
116 struct Adapter<'a,T: ?Sized +'a>(&'a mut T);
118 impl<'a, T: ?Sized> Write for Adapter<'a, T>
121 fn write_str(&mut self, s: &str) -> Result {
125 fn write_char(&mut self, c: char) -> Result {
129 fn write_fmt(&mut self, args: Arguments) -> Result {
130 self.0.write_fmt(args)
134 write(&mut Adapter(self), args)
138 #[stable(feature = "fmt_write_blanket_impl", since = "1.4.0")]
139 impl<'a, W: Write + ?Sized> Write for &'a mut W {
140 fn write_str(&mut self, s: &str) -> Result {
141 (**self).write_str(s)
144 fn write_char(&mut self, c: char) -> Result {
145 (**self).write_char(c)
148 fn write_fmt(&mut self, args: Arguments) -> Result {
149 (**self).write_fmt(args)
153 /// A struct to represent both where to emit formatting strings to and how they
154 /// should be formatted. A mutable version of this is passed to all formatting
156 #[allow(missing_debug_implementations)]
157 #[stable(feature = "rust1", since = "1.0.0")]
158 pub struct Formatter<'a> {
161 align: rt::v1::Alignment,
162 width: Option<usize>,
163 precision: Option<usize>,
165 buf: &'a mut (Write+'a),
166 curarg: slice::Iter<'a, ArgumentV1<'a>>,
167 args: &'a [ArgumentV1<'a>],
170 // NB. Argument is essentially an optimized partially applied formatting function,
171 // equivalent to `exists T.(&T, fn(&T, &mut Formatter) -> Result`.
175 /// This struct represents the generic "argument" which is taken by the Xprintf
176 /// family of functions. It contains a function to format the given value. At
177 /// compile time it is ensured that the function and the value have the correct
178 /// types, and then this struct is used to canonicalize arguments to one type.
180 #[allow(missing_debug_implementations)]
181 #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
184 pub struct ArgumentV1<'a> {
186 formatter: fn(&Void, &mut Formatter) -> Result,
189 #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
191 impl<'a> Clone for ArgumentV1<'a> {
192 fn clone(&self) -> ArgumentV1<'a> {
197 impl<'a> ArgumentV1<'a> {
199 fn show_usize(x: &usize, f: &mut Formatter) -> Result {
204 #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
206 pub fn new<'b, T>(x: &'b T,
207 f: fn(&T, &mut Formatter) -> Result) -> ArgumentV1<'b> {
210 formatter: mem::transmute(f),
211 value: mem::transmute(x)
217 #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
219 pub fn from_usize(x: &usize) -> ArgumentV1 {
220 ArgumentV1::new(x, ArgumentV1::show_usize)
223 fn as_usize(&self) -> Option<usize> {
224 if self.formatter as usize == ArgumentV1::show_usize as usize {
225 Some(unsafe { *(self.value as *const _ as *const usize) })
232 // flags available in the v1 format of format_args
233 #[derive(Copy, Clone)]
234 #[allow(dead_code)] // SignMinus isn't currently used
235 enum FlagV1 { SignPlus, SignMinus, Alternate, SignAwareZeroPad, }
237 impl<'a> Arguments<'a> {
238 /// When using the format_args!() macro, this function is used to generate the
239 /// Arguments structure.
240 #[doc(hidden)] #[inline]
241 #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
243 pub fn new_v1(pieces: &'a [&'a str],
244 args: &'a [ArgumentV1<'a>]) -> Arguments<'a> {
252 /// This function is used to specify nonstandard formatting parameters.
253 /// The `pieces` array must be at least as long as `fmt` to construct
254 /// a valid Arguments structure. Also, any `Count` within `fmt` that is
255 /// `CountIsParam` or `CountIsNextParam` has to point to an argument
256 /// created with `argumentusize`. However, failing to do so doesn't cause
257 /// unsafety, but will ignore invalid .
258 #[doc(hidden)] #[inline]
259 #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
261 pub fn new_v1_formatted(pieces: &'a [&'a str],
262 args: &'a [ArgumentV1<'a>],
263 fmt: &'a [rt::v1::Argument]) -> Arguments<'a> {
272 /// This structure represents a safely precompiled version of a format string
273 /// and its arguments. This cannot be generated at runtime because it cannot
274 /// safely be done so, so no constructors are given and the fields are private
275 /// to prevent modification.
277 /// The `format_args!` macro will safely create an instance of this structure
278 /// and pass it to a function or closure, passed as the first argument. The
279 /// macro validates the format string at compile-time so usage of the `write`
280 /// and `format` functions can be safely performed.
281 #[stable(feature = "rust1", since = "1.0.0")]
282 #[derive(Copy, Clone)]
283 pub struct Arguments<'a> {
284 // Format string pieces to print.
285 pieces: &'a [&'a str],
287 // Placeholder specs, or `None` if all specs are default (as in "{}{}").
288 fmt: Option<&'a [rt::v1::Argument]>,
290 // Dynamic arguments for interpolation, to be interleaved with string
291 // pieces. (Every argument is preceded by a string piece.)
292 args: &'a [ArgumentV1<'a>],
295 #[stable(feature = "rust1", since = "1.0.0")]
296 impl<'a> Debug for Arguments<'a> {
297 fn fmt(&self, fmt: &mut Formatter) -> Result {
298 Display::fmt(self, fmt)
302 #[stable(feature = "rust1", since = "1.0.0")]
303 impl<'a> Display for Arguments<'a> {
304 fn fmt(&self, fmt: &mut Formatter) -> Result {
305 write(fmt.buf, *self)
309 /// Format trait for the `?` character.
311 /// `Debug` should format the output in a programmer-facing, debugging context.
313 /// Generally speaking, you should just `derive` a `Debug` implementation.
315 /// When used with the alternate format specifier `#?`, the output is pretty-printed.
317 /// For more information on formatters, see [the module-level documentation][module].
319 /// [module]: ../../std/fmt/index.html
321 /// This trait can be used with `#[derive]` if all fields implement `Debug`. When
322 /// `derive`d for structs, it will use the name of the `struct`, then `{`, then a
323 /// comma-separated list of each field's name and `Debug` value, then `}`. For
324 /// `enum`s, it will use the name of the variant and, if applicable, `(`, then the
325 /// `Debug` values of the fields, then `)`.
329 /// Deriving an implementation:
338 /// let origin = Point { x: 0, y: 0 };
340 /// println!("The origin is: {:?}", origin);
343 /// Manually implementing:
353 /// impl fmt::Debug for Point {
354 /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
355 /// write!(f, "Point {{ x: {}, y: {} }}", self.x, self.y)
359 /// let origin = Point { x: 0, y: 0 };
361 /// println!("The origin is: {:?}", origin);
367 /// The origin is: Point { x: 0, y: 0 }
370 /// There are a number of `debug_*` methods on `Formatter` to help you with manual
371 /// implementations, such as [`debug_struct`][debug_struct].
373 /// `Debug` implementations using either `derive` or the debug builder API
374 /// on `Formatter` support pretty printing using the alternate flag: `{:#?}`.
376 /// [debug_struct]: ../../std/fmt/struct.Formatter.html#method.debug_struct
378 /// Pretty printing with `#?`:
387 /// let origin = Point { x: 0, y: 0 };
389 /// println!("The origin is: {:#?}", origin);
395 /// The origin is: Point {
400 #[stable(feature = "rust1", since = "1.0.0")]
401 #[rustc_on_unimplemented = "`{Self}` cannot be formatted using `:?`; if it is \
402 defined in your crate, add `#[derive(Debug)]` or \
403 manually implement it"]
404 #[lang = "debug_trait"]
406 /// Formats the value using the given formatter.
407 #[stable(feature = "rust1", since = "1.0.0")]
408 fn fmt(&self, &mut Formatter) -> Result;
411 /// Format trait for an empty format, `{}`.
413 /// `Display` is similar to [`Debug`][debug], but `Display` is for user-facing
414 /// output, and so cannot be derived.
416 /// [debug]: trait.Debug.html
418 /// For more information on formatters, see [the module-level documentation][module].
420 /// [module]: ../../std/fmt/index.html
424 /// Implementing `Display` on a type:
434 /// impl fmt::Display for Point {
435 /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
436 /// write!(f, "({}, {})", self.x, self.y)
440 /// let origin = Point { x: 0, y: 0 };
442 /// println!("The origin is: {}", origin);
444 #[rustc_on_unimplemented = "`{Self}` cannot be formatted with the default \
445 formatter; try using `:?` instead if you are using \
447 #[stable(feature = "rust1", since = "1.0.0")]
449 /// Formats the value using the given formatter.
450 #[stable(feature = "rust1", since = "1.0.0")]
451 fn fmt(&self, &mut Formatter) -> Result;
454 /// Format trait for the `o` character.
456 /// The `Octal` trait should format its output as a number in base-8.
458 /// The alternate flag, `#`, adds a `0o` in front of the output.
460 /// For more information on formatters, see [the module-level documentation][module].
462 /// [module]: ../../std/fmt/index.html
466 /// Basic usage with `i32`:
469 /// let x = 42; // 42 is '52' in octal
471 /// assert_eq!(format!("{:o}", x), "52");
472 /// assert_eq!(format!("{:#o}", x), "0o52");
475 /// Implementing `Octal` on a type:
480 /// struct Length(i32);
482 /// impl fmt::Octal for Length {
483 /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
484 /// let val = self.0;
486 /// write!(f, "{:o}", val) // delegate to i32's implementation
490 /// let l = Length(9);
492 /// println!("l as octal is: {:o}", l);
494 #[stable(feature = "rust1", since = "1.0.0")]
496 /// Formats the value using the given formatter.
497 #[stable(feature = "rust1", since = "1.0.0")]
498 fn fmt(&self, &mut Formatter) -> Result;
501 /// Format trait for the `b` character.
503 /// The `Binary` trait should format its output as a number in binary.
505 /// The alternate flag, `#`, adds a `0b` in front of the output.
507 /// For more information on formatters, see [the module-level documentation][module].
509 /// [module]: ../../std/fmt/index.html
513 /// Basic usage with `i32`:
516 /// let x = 42; // 42 is '101010' in binary
518 /// assert_eq!(format!("{:b}", x), "101010");
519 /// assert_eq!(format!("{:#b}", x), "0b101010");
522 /// Implementing `Binary` on a type:
527 /// struct Length(i32);
529 /// impl fmt::Binary for Length {
530 /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
531 /// let val = self.0;
533 /// write!(f, "{:b}", val) // delegate to i32's implementation
537 /// let l = Length(107);
539 /// println!("l as binary is: {:b}", l);
541 #[stable(feature = "rust1", since = "1.0.0")]
543 /// Formats the value using the given formatter.
544 #[stable(feature = "rust1", since = "1.0.0")]
545 fn fmt(&self, &mut Formatter) -> Result;
548 /// Format trait for the `x` character.
550 /// The `LowerHex` trait should format its output as a number in hexadecimal, with `a` through `f`
553 /// The alternate flag, `#`, adds a `0x` in front of the output.
555 /// For more information on formatters, see [the module-level documentation][module].
557 /// [module]: ../../std/fmt/index.html
561 /// Basic usage with `i32`:
564 /// let x = 42; // 42 is '2a' in hex
566 /// assert_eq!(format!("{:x}", x), "2a");
567 /// assert_eq!(format!("{:#x}", x), "0x2a");
570 /// Implementing `LowerHex` on a type:
575 /// struct Length(i32);
577 /// impl fmt::LowerHex for Length {
578 /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
579 /// let val = self.0;
581 /// write!(f, "{:x}", val) // delegate to i32's implementation
585 /// let l = Length(9);
587 /// println!("l as hex is: {:x}", l);
589 #[stable(feature = "rust1", since = "1.0.0")]
591 /// Formats the value using the given formatter.
592 #[stable(feature = "rust1", since = "1.0.0")]
593 fn fmt(&self, &mut Formatter) -> Result;
596 /// Format trait for the `X` character.
598 /// The `UpperHex` trait should format its output as a number in hexadecimal, with `A` through `F`
601 /// The alternate flag, `#`, adds a `0x` in front of the output.
603 /// For more information on formatters, see [the module-level documentation][module].
605 /// [module]: ../../std/fmt/index.html
609 /// Basic usage with `i32`:
612 /// let x = 42; // 42 is '2A' in hex
614 /// assert_eq!(format!("{:X}", x), "2A");
615 /// assert_eq!(format!("{:#X}", x), "0x2A");
618 /// Implementing `UpperHex` on a type:
623 /// struct Length(i32);
625 /// impl fmt::UpperHex for Length {
626 /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
627 /// let val = self.0;
629 /// write!(f, "{:X}", val) // delegate to i32's implementation
633 /// let l = Length(9);
635 /// println!("l as hex is: {:X}", l);
637 #[stable(feature = "rust1", since = "1.0.0")]
639 /// Formats the value using the given formatter.
640 #[stable(feature = "rust1", since = "1.0.0")]
641 fn fmt(&self, &mut Formatter) -> Result;
644 /// Format trait for the `p` character.
646 /// The `Pointer` trait should format its output as a memory location. This is commonly presented
649 /// For more information on formatters, see [the module-level documentation][module].
651 /// [module]: ../../std/fmt/index.html
655 /// Basic usage with `&i32`:
660 /// let address = format!("{:p}", x); // this produces something like '0x7f06092ac6d0'
663 /// Implementing `Pointer` on a type:
668 /// struct Length(i32);
670 /// impl fmt::Pointer for Length {
671 /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
672 /// // use `as` to convert to a `*const T`, which implements Pointer, which we can use
674 /// write!(f, "{:p}", self as *const Length)
678 /// let l = Length(42);
680 /// println!("l is in memory here: {:p}", l);
682 #[stable(feature = "rust1", since = "1.0.0")]
684 /// Formats the value using the given formatter.
685 #[stable(feature = "rust1", since = "1.0.0")]
686 fn fmt(&self, &mut Formatter) -> Result;
689 /// Format trait for the `e` character.
691 /// The `LowerExp` trait should format its output in scientific notation with a lower-case `e`.
693 /// For more information on formatters, see [the module-level documentation][module].
695 /// [module]: ../../std/fmt/index.html
699 /// Basic usage with `i32`:
702 /// let x = 42.0; // 42.0 is '4.2e1' in scientific notation
704 /// assert_eq!(format!("{:e}", x), "4.2e1");
707 /// Implementing `LowerExp` on a type:
712 /// struct Length(i32);
714 /// impl fmt::LowerExp for Length {
715 /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
716 /// let val = self.0;
717 /// write!(f, "{}e1", val / 10)
721 /// let l = Length(100);
723 /// println!("l in scientific notation is: {:e}", l);
725 #[stable(feature = "rust1", since = "1.0.0")]
727 /// Formats the value using the given formatter.
728 #[stable(feature = "rust1", since = "1.0.0")]
729 fn fmt(&self, &mut Formatter) -> Result;
732 /// Format trait for the `E` character.
734 /// The `UpperExp` trait should format its output in scientific notation with an upper-case `E`.
736 /// For more information on formatters, see [the module-level documentation][module].
738 /// [module]: ../../std/fmt/index.html
742 /// Basic usage with `f32`:
745 /// let x = 42.0; // 42.0 is '4.2E1' in scientific notation
747 /// assert_eq!(format!("{:E}", x), "4.2E1");
750 /// Implementing `UpperExp` on a type:
755 /// struct Length(i32);
757 /// impl fmt::UpperExp for Length {
758 /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
759 /// let val = self.0;
760 /// write!(f, "{}E1", val / 10)
764 /// let l = Length(100);
766 /// println!("l in scientific notation is: {:E}", l);
768 #[stable(feature = "rust1", since = "1.0.0")]
770 /// Formats the value using the given formatter.
771 #[stable(feature = "rust1", since = "1.0.0")]
772 fn fmt(&self, &mut Formatter) -> Result;
775 /// The `write` function takes an output stream, a precompiled format string,
776 /// and a list of arguments. The arguments will be formatted according to the
777 /// specified format string into the output stream provided.
781 /// * output - the buffer to write output to
782 /// * args - the precompiled arguments generated by `format_args!`
791 /// let mut output = String::new();
792 /// fmt::write(&mut output, format_args!("Hello {}!", "world"))
793 /// .expect("Error occurred while trying to write in String");
794 /// assert_eq!(output, "Hello world!");
797 /// Please note that using [`write!`][write_macro] might be preferrable. Example:
800 /// use std::fmt::Write;
802 /// let mut output = String::new();
803 /// write!(&mut output, "Hello {}!", "world")
804 /// .expect("Error occurred while trying to write in String");
805 /// assert_eq!(output, "Hello world!");
808 /// [write_macro]: ../../std/macro.write!.html
809 #[stable(feature = "rust1", since = "1.0.0")]
810 pub fn write(output: &mut Write, args: Arguments) -> Result {
811 let mut formatter = Formatter {
816 align: rt::v1::Alignment::Unknown,
819 curarg: args.args.iter(),
822 let mut pieces = args.pieces.iter();
826 // We can use default formatting parameters for all arguments.
827 for (arg, piece) in args.args.iter().zip(pieces.by_ref()) {
828 formatter.buf.write_str(*piece)?;
829 (arg.formatter)(arg.value, &mut formatter)?;
833 // Every spec has a corresponding argument that is preceded by
835 for (arg, piece) in fmt.iter().zip(pieces.by_ref()) {
836 formatter.buf.write_str(*piece)?;
842 // There can be only one trailing string piece left.
843 if let Some(piece) = pieces.next() {
844 formatter.buf.write_str(*piece)?;
850 impl<'a> Formatter<'a> {
852 // First up is the collection of functions used to execute a format string
853 // at runtime. This consumes all of the compile-time statics generated by
854 // the format! syntax extension.
855 fn run(&mut self, arg: &rt::v1::Argument) -> Result {
856 // Fill in the format parameters into the formatter
857 self.fill = arg.format.fill;
858 self.align = arg.format.align;
859 self.flags = arg.format.flags;
860 self.width = self.getcount(&arg.format.width);
861 self.precision = self.getcount(&arg.format.precision);
863 // Extract the correct argument
864 let value = match arg.position {
865 rt::v1::Position::Next => { *self.curarg.next().unwrap() }
866 rt::v1::Position::At(i) => self.args[i],
869 // Then actually do some printing
870 (value.formatter)(value.value, self)
873 fn getcount(&mut self, cnt: &rt::v1::Count) -> Option<usize> {
875 rt::v1::Count::Is(n) => Some(n),
876 rt::v1::Count::Implied => None,
877 rt::v1::Count::Param(i) => {
878 self.args[i].as_usize()
880 rt::v1::Count::NextParam => {
881 self.curarg.next().and_then(|arg| arg.as_usize())
886 // Helper methods used for padding and processing formatting arguments that
887 // all formatting traits can use.
889 /// Performs the correct padding for an integer which has already been
890 /// emitted into a str. The str should *not* contain the sign for the
891 /// integer, that will be added by this method.
895 /// * is_nonnegative - whether the original integer was either positive or zero.
896 /// * prefix - if the '#' character (Alternate) is provided, this
897 /// is the prefix to put in front of the number.
898 /// * buf - the byte array that the number has been formatted into
900 /// This function will correctly account for the flags provided as well as
901 /// the minimum width. It will not take precision into account.
902 #[stable(feature = "rust1", since = "1.0.0")]
903 pub fn pad_integral(&mut self,
904 is_nonnegative: bool,
910 let mut width = buf.len();
914 sign = Some('-'); width += 1;
915 } else if self.sign_plus() {
916 sign = Some('+'); width += 1;
919 let mut prefixed = false;
920 if self.alternate() {
921 prefixed = true; width += prefix.chars().count();
924 // Writes the sign if it exists, and then the prefix if it was requested
925 let write_prefix = |f: &mut Formatter| {
926 if let Some(c) = sign {
927 f.buf.write_str(unsafe {
928 str::from_utf8_unchecked(c.encode_utf8().as_slice())
931 if prefixed { f.buf.write_str(prefix) }
935 // The `width` field is more of a `min-width` parameter at this point.
937 // If there's no minimum length requirements then we can just
940 write_prefix(self)?; self.buf.write_str(buf)
942 // Check if we're over the minimum width, if so then we can also
943 // just write the bytes.
944 Some(min) if width >= min => {
945 write_prefix(self)?; self.buf.write_str(buf)
947 // The sign and prefix goes before the padding if the fill character
949 Some(min) if self.sign_aware_zero_pad() => {
952 self.with_padding(min - width, rt::v1::Alignment::Right, |f| {
956 // Otherwise, the sign and prefix goes after the padding
958 self.with_padding(min - width, rt::v1::Alignment::Right, |f| {
959 write_prefix(f)?; f.buf.write_str(buf)
965 /// This function takes a string slice and emits it to the internal buffer
966 /// after applying the relevant formatting flags specified. The flags
967 /// recognized for generic strings are:
969 /// * width - the minimum width of what to emit
970 /// * fill/align - what to emit and where to emit it if the string
971 /// provided needs to be padded
972 /// * precision - the maximum length to emit, the string is truncated if it
973 /// is longer than this length
975 /// Notably this function ignored the `flag` parameters
976 #[stable(feature = "rust1", since = "1.0.0")]
977 pub fn pad(&mut self, s: &str) -> Result {
978 // Make sure there's a fast path up front
979 if self.width.is_none() && self.precision.is_none() {
980 return self.buf.write_str(s);
982 // The `precision` field can be interpreted as a `max-width` for the
983 // string being formatted.
984 let s = if let Some(max) = self.precision {
985 // If our string is longer that the precision, then we must have
986 // truncation. However other flags like `fill`, `width` and `align`
987 // must act as always.
988 if let Some((i, _)) = s.char_indices().skip(max).next() {
996 // The `width` field is more of a `min-width` parameter at this point.
998 // If we're under the maximum length, and there's no minimum length
999 // requirements, then we can just emit the string
1000 None => self.buf.write_str(s),
1001 // If we're under the maximum width, check if we're over the minimum
1002 // width, if so it's as easy as just emitting the string.
1003 Some(width) if s.chars().count() >= width => {
1004 self.buf.write_str(s)
1006 // If we're under both the maximum and the minimum width, then fill
1007 // up the minimum width with the specified string + some alignment.
1009 let align = rt::v1::Alignment::Left;
1010 self.with_padding(width - s.chars().count(), align, |me| {
1017 /// Runs a callback, emitting the correct padding either before or
1018 /// afterwards depending on whether right or left alignment is requested.
1019 fn with_padding<F>(&mut self, padding: usize, default: rt::v1::Alignment,
1021 where F: FnOnce(&mut Formatter) -> Result,
1024 let align = match self.align {
1025 rt::v1::Alignment::Unknown => default,
1029 let (pre_pad, post_pad) = match align {
1030 rt::v1::Alignment::Left => (0, padding),
1031 rt::v1::Alignment::Right |
1032 rt::v1::Alignment::Unknown => (padding, 0),
1033 rt::v1::Alignment::Center => (padding / 2, (padding + 1) / 2),
1036 let fill = self.fill.encode_utf8();
1038 str::from_utf8_unchecked(fill.as_slice())
1041 for _ in 0..pre_pad {
1042 self.buf.write_str(fill)?;
1047 for _ in 0..post_pad {
1048 self.buf.write_str(fill)?;
1054 /// Takes the formatted parts and applies the padding.
1055 /// Assumes that the caller already has rendered the parts with required precision,
1056 /// so that `self.precision` can be ignored.
1057 fn pad_formatted_parts(&mut self, formatted: &flt2dec::Formatted) -> Result {
1058 if let Some(mut width) = self.width {
1059 // for the sign-aware zero padding, we render the sign first and
1060 // behave as if we had no sign from the beginning.
1061 let mut formatted = formatted.clone();
1062 let mut align = self.align;
1063 let old_fill = self.fill;
1064 if self.sign_aware_zero_pad() {
1065 // a sign always goes first
1066 let sign = unsafe { str::from_utf8_unchecked(formatted.sign) };
1067 self.buf.write_str(sign)?;
1069 // remove the sign from the formatted parts
1070 formatted.sign = b"";
1071 width = if width < sign.len() { 0 } else { width - sign.len() };
1072 align = rt::v1::Alignment::Right;
1076 // remaining parts go through the ordinary padding process.
1077 let len = formatted.len();
1078 let ret = if width <= len { // no padding
1079 self.write_formatted_parts(&formatted)
1081 self.with_padding(width - len, align, |f| {
1082 f.write_formatted_parts(&formatted)
1085 self.fill = old_fill;
1088 // this is the common case and we take a shortcut
1089 self.write_formatted_parts(formatted)
1093 fn write_formatted_parts(&mut self, formatted: &flt2dec::Formatted) -> Result {
1094 fn write_bytes(buf: &mut Write, s: &[u8]) -> Result {
1095 buf.write_str(unsafe { str::from_utf8_unchecked(s) })
1098 if !formatted.sign.is_empty() {
1099 write_bytes(self.buf, formatted.sign)?;
1101 for part in formatted.parts {
1103 flt2dec::Part::Zero(mut nzeroes) => {
1104 const ZEROES: &'static str = // 64 zeroes
1105 "0000000000000000000000000000000000000000000000000000000000000000";
1106 while nzeroes > ZEROES.len() {
1107 self.buf.write_str(ZEROES)?;
1108 nzeroes -= ZEROES.len();
1111 self.buf.write_str(&ZEROES[..nzeroes])?;
1114 flt2dec::Part::Num(mut v) => {
1116 let len = part.len();
1117 for c in s[..len].iter_mut().rev() {
1118 *c = b'0' + (v % 10) as u8;
1121 write_bytes(self.buf, &s[..len])?;
1123 flt2dec::Part::Copy(buf) => {
1124 write_bytes(self.buf, buf)?;
1131 /// Writes some data to the underlying buffer contained within this
1133 #[stable(feature = "rust1", since = "1.0.0")]
1134 pub fn write_str(&mut self, data: &str) -> Result {
1135 self.buf.write_str(data)
1138 /// Writes some formatted information into this instance
1139 #[stable(feature = "rust1", since = "1.0.0")]
1140 pub fn write_fmt(&mut self, fmt: Arguments) -> Result {
1141 write(self.buf, fmt)
1144 /// Flags for formatting (packed version of rt::Flag)
1145 #[stable(feature = "rust1", since = "1.0.0")]
1146 pub fn flags(&self) -> u32 { self.flags }
1148 /// Character used as 'fill' whenever there is alignment
1149 #[stable(feature = "fmt_flags", since = "1.5.0")]
1150 pub fn fill(&self) -> char { self.fill }
1152 /// Flag indicating what form of alignment was requested
1153 #[unstable(feature = "fmt_flags_align", reason = "method was just created",
1155 pub fn align(&self) -> Alignment {
1157 rt::v1::Alignment::Left => Alignment::Left,
1158 rt::v1::Alignment::Right => Alignment::Right,
1159 rt::v1::Alignment::Center => Alignment::Center,
1160 rt::v1::Alignment::Unknown => Alignment::Unknown,
1164 /// Optionally specified integer width that the output should be
1165 #[stable(feature = "fmt_flags", since = "1.5.0")]
1166 pub fn width(&self) -> Option<usize> { self.width }
1168 /// Optionally specified precision for numeric types
1169 #[stable(feature = "fmt_flags", since = "1.5.0")]
1170 pub fn precision(&self) -> Option<usize> { self.precision }
1172 /// Determines if the `+` flag was specified.
1173 #[stable(feature = "fmt_flags", since = "1.5.0")]
1174 pub fn sign_plus(&self) -> bool { self.flags & (1 << FlagV1::SignPlus as u32) != 0 }
1176 /// Determines if the `-` flag was specified.
1177 #[stable(feature = "fmt_flags", since = "1.5.0")]
1178 pub fn sign_minus(&self) -> bool { self.flags & (1 << FlagV1::SignMinus as u32) != 0 }
1180 /// Determines if the `#` flag was specified.
1181 #[stable(feature = "fmt_flags", since = "1.5.0")]
1182 pub fn alternate(&self) -> bool { self.flags & (1 << FlagV1::Alternate as u32) != 0 }
1184 /// Determines if the `0` flag was specified.
1185 #[stable(feature = "fmt_flags", since = "1.5.0")]
1186 pub fn sign_aware_zero_pad(&self) -> bool {
1187 self.flags & (1 << FlagV1::SignAwareZeroPad as u32) != 0
1190 /// Creates a `DebugStruct` builder designed to assist with creation of
1191 /// `fmt::Debug` implementations for structs.
1203 /// impl fmt::Debug for Foo {
1204 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
1205 /// fmt.debug_struct("Foo")
1206 /// .field("bar", &self.bar)
1207 /// .field("baz", &self.baz)
1212 /// // prints "Foo { bar: 10, baz: "Hello World" }"
1213 /// println!("{:?}", Foo { bar: 10, baz: "Hello World".to_string() });
1215 #[stable(feature = "debug_builders", since = "1.2.0")]
1217 pub fn debug_struct<'b>(&'b mut self, name: &str) -> DebugStruct<'b, 'a> {
1218 builders::debug_struct_new(self, name)
1221 /// Creates a `DebugTuple` builder designed to assist with creation of
1222 /// `fmt::Debug` implementations for tuple structs.
1229 /// struct Foo(i32, String);
1231 /// impl fmt::Debug for Foo {
1232 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
1233 /// fmt.debug_tuple("Foo")
1240 /// // prints "Foo(10, "Hello World")"
1241 /// println!("{:?}", Foo(10, "Hello World".to_string()));
1243 #[stable(feature = "debug_builders", since = "1.2.0")]
1245 pub fn debug_tuple<'b>(&'b mut self, name: &str) -> DebugTuple<'b, 'a> {
1246 builders::debug_tuple_new(self, name)
1249 /// Creates a `DebugList` builder designed to assist with creation of
1250 /// `fmt::Debug` implementations for list-like structures.
1257 /// struct Foo(Vec<i32>);
1259 /// impl fmt::Debug for Foo {
1260 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
1261 /// fmt.debug_list().entries(self.0.iter()).finish()
1265 /// // prints "[10, 11]"
1266 /// println!("{:?}", Foo(vec![10, 11]));
1268 #[stable(feature = "debug_builders", since = "1.2.0")]
1270 pub fn debug_list<'b>(&'b mut self) -> DebugList<'b, 'a> {
1271 builders::debug_list_new(self)
1274 /// Creates a `DebugSet` builder designed to assist with creation of
1275 /// `fmt::Debug` implementations for set-like structures.
1282 /// struct Foo(Vec<i32>);
1284 /// impl fmt::Debug for Foo {
1285 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
1286 /// fmt.debug_set().entries(self.0.iter()).finish()
1290 /// // prints "{10, 11}"
1291 /// println!("{:?}", Foo(vec![10, 11]));
1293 #[stable(feature = "debug_builders", since = "1.2.0")]
1295 pub fn debug_set<'b>(&'b mut self) -> DebugSet<'b, 'a> {
1296 builders::debug_set_new(self)
1299 /// Creates a `DebugMap` builder designed to assist with creation of
1300 /// `fmt::Debug` implementations for map-like structures.
1307 /// struct Foo(Vec<(String, i32)>);
1309 /// impl fmt::Debug for Foo {
1310 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
1311 /// fmt.debug_map().entries(self.0.iter().map(|&(ref k, ref v)| (k, v))).finish()
1315 /// // prints "{"A": 10, "B": 11}"
1316 /// println!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)]));
1318 #[stable(feature = "debug_builders", since = "1.2.0")]
1320 pub fn debug_map<'b>(&'b mut self) -> DebugMap<'b, 'a> {
1321 builders::debug_map_new(self)
1325 #[stable(since = "1.2.0", feature = "formatter_write")]
1326 impl<'a> Write for Formatter<'a> {
1327 fn write_str(&mut self, s: &str) -> Result {
1328 self.buf.write_str(s)
1331 fn write_char(&mut self, c: char) -> Result {
1332 self.buf.write_char(c)
1335 fn write_fmt(&mut self, args: Arguments) -> Result {
1336 write(self.buf, args)
1340 #[stable(feature = "rust1", since = "1.0.0")]
1341 impl Display for Error {
1342 fn fmt(&self, f: &mut Formatter) -> Result {
1343 Display::fmt("an error occurred when formatting an argument", f)
1347 // Implementations of the core formatting traits
1349 macro_rules! fmt_refs {
1350 ($($tr:ident),*) => {
1352 #[stable(feature = "rust1", since = "1.0.0")]
1353 impl<'a, T: ?Sized + $tr> $tr for &'a T {
1354 fn fmt(&self, f: &mut Formatter) -> Result { $tr::fmt(&**self, f) }
1356 #[stable(feature = "rust1", since = "1.0.0")]
1357 impl<'a, T: ?Sized + $tr> $tr for &'a mut T {
1358 fn fmt(&self, f: &mut Formatter) -> Result { $tr::fmt(&**self, f) }
1364 fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp }
1366 #[stable(feature = "rust1", since = "1.0.0")]
1367 impl Debug for bool {
1368 fn fmt(&self, f: &mut Formatter) -> Result {
1369 Display::fmt(self, f)
1373 #[stable(feature = "rust1", since = "1.0.0")]
1374 impl Display for bool {
1375 fn fmt(&self, f: &mut Formatter) -> Result {
1376 Display::fmt(if *self { "true" } else { "false" }, f)
1380 #[stable(feature = "rust1", since = "1.0.0")]
1381 impl Debug for str {
1382 fn fmt(&self, f: &mut Formatter) -> Result {
1385 for (i, c) in self.char_indices() {
1386 let esc = c.escape_debug();
1387 // If char needs escaping, flush backlog so far and write, else skip
1389 f.write_str(&self[from..i])?;
1393 from = i + c.len_utf8();
1396 f.write_str(&self[from..])?;
1401 #[stable(feature = "rust1", since = "1.0.0")]
1402 impl Display for str {
1403 fn fmt(&self, f: &mut Formatter) -> Result {
1408 #[stable(feature = "rust1", since = "1.0.0")]
1409 impl Debug for char {
1410 fn fmt(&self, f: &mut Formatter) -> Result {
1411 f.write_char('\'')?;
1412 for c in self.escape_debug() {
1419 #[stable(feature = "rust1", since = "1.0.0")]
1420 impl Display for char {
1421 fn fmt(&self, f: &mut Formatter) -> Result {
1422 if f.width.is_none() && f.precision.is_none() {
1426 str::from_utf8_unchecked(self.encode_utf8().as_slice())
1432 #[stable(feature = "rust1", since = "1.0.0")]
1433 impl<T: ?Sized> Pointer for *const T {
1434 fn fmt(&self, f: &mut Formatter) -> Result {
1435 let old_width = f.width;
1436 let old_flags = f.flags;
1438 // The alternate flag is already treated by LowerHex as being special-
1439 // it denotes whether to prefix with 0x. We use it to work out whether
1440 // or not to zero extend, and then unconditionally set it to get the
1443 f.flags |= 1 << (FlagV1::SignAwareZeroPad as u32);
1445 if let None = f.width {
1446 f.width = Some(((mem::size_of::<usize>() * 8) / 4) + 2);
1449 f.flags |= 1 << (FlagV1::Alternate as u32);
1451 let ret = LowerHex::fmt(&(*self as *const () as usize), f);
1453 f.width = old_width;
1454 f.flags = old_flags;
1460 #[stable(feature = "rust1", since = "1.0.0")]
1461 impl<T: ?Sized> Pointer for *mut T {
1462 fn fmt(&self, f: &mut Formatter) -> Result {
1463 Pointer::fmt(&(*self as *const T), f)
1467 #[stable(feature = "rust1", since = "1.0.0")]
1468 impl<'a, T: ?Sized> Pointer for &'a T {
1469 fn fmt(&self, f: &mut Formatter) -> Result {
1470 Pointer::fmt(&(*self as *const T), f)
1474 #[stable(feature = "rust1", since = "1.0.0")]
1475 impl<'a, T: ?Sized> Pointer for &'a mut T {
1476 fn fmt(&self, f: &mut Formatter) -> Result {
1477 Pointer::fmt(&(&**self as *const T), f)
1481 // Common code of floating point Debug and Display.
1482 fn float_to_decimal_common<T>(fmt: &mut Formatter, num: &T, negative_zero: bool) -> Result
1483 where T: flt2dec::DecodableFloat
1485 let force_sign = fmt.sign_plus();
1486 let sign = match (force_sign, negative_zero) {
1487 (false, false) => flt2dec::Sign::Minus,
1488 (false, true) => flt2dec::Sign::MinusRaw,
1489 (true, false) => flt2dec::Sign::MinusPlus,
1490 (true, true) => flt2dec::Sign::MinusPlusRaw,
1493 let mut buf = [0; 1024]; // enough for f32 and f64
1494 let mut parts = [flt2dec::Part::Zero(0); 16];
1495 let formatted = if let Some(precision) = fmt.precision {
1496 flt2dec::to_exact_fixed_str(flt2dec::strategy::grisu::format_exact, *num, sign,
1497 precision, false, &mut buf, &mut parts)
1499 flt2dec::to_shortest_str(flt2dec::strategy::grisu::format_shortest, *num, sign,
1500 0, false, &mut buf, &mut parts)
1502 fmt.pad_formatted_parts(&formatted)
1505 // Common code of floating point LowerExp and UpperExp.
1506 fn float_to_exponential_common<T>(fmt: &mut Formatter, num: &T, upper: bool) -> Result
1507 where T: flt2dec::DecodableFloat
1509 let force_sign = fmt.sign_plus();
1510 let sign = match force_sign {
1511 false => flt2dec::Sign::Minus,
1512 true => flt2dec::Sign::MinusPlus,
1515 let mut buf = [0; 1024]; // enough for f32 and f64
1516 let mut parts = [flt2dec::Part::Zero(0); 16];
1517 let formatted = if let Some(precision) = fmt.precision {
1518 // 1 integral digit + `precision` fractional digits = `precision + 1` total digits
1519 flt2dec::to_exact_exp_str(flt2dec::strategy::grisu::format_exact, *num, sign,
1520 precision + 1, upper, &mut buf, &mut parts)
1522 flt2dec::to_shortest_exp_str(flt2dec::strategy::grisu::format_shortest, *num, sign,
1523 (0, 0), upper, &mut buf, &mut parts)
1525 fmt.pad_formatted_parts(&formatted)
1528 macro_rules! floating { ($ty:ident) => {
1530 #[stable(feature = "rust1", since = "1.0.0")]
1531 impl Debug for $ty {
1532 fn fmt(&self, fmt: &mut Formatter) -> Result {
1533 float_to_decimal_common(fmt, self, true)
1537 #[stable(feature = "rust1", since = "1.0.0")]
1538 impl Display for $ty {
1539 fn fmt(&self, fmt: &mut Formatter) -> Result {
1540 float_to_decimal_common(fmt, self, false)
1544 #[stable(feature = "rust1", since = "1.0.0")]
1545 impl LowerExp for $ty {
1546 fn fmt(&self, fmt: &mut Formatter) -> Result {
1547 float_to_exponential_common(fmt, self, false)
1551 #[stable(feature = "rust1", since = "1.0.0")]
1552 impl UpperExp for $ty {
1553 fn fmt(&self, fmt: &mut Formatter) -> Result {
1554 float_to_exponential_common(fmt, self, true)
1561 // Implementation of Display/Debug for various core types
1563 #[stable(feature = "rust1", since = "1.0.0")]
1564 impl<T> Debug for *const T {
1565 fn fmt(&self, f: &mut Formatter) -> Result { Pointer::fmt(self, f) }
1567 #[stable(feature = "rust1", since = "1.0.0")]
1568 impl<T> Debug for *mut T {
1569 fn fmt(&self, f: &mut Formatter) -> Result { Pointer::fmt(self, f) }
1573 ($name:ident, $($other:ident,)*) => (tuple! { $($other,)* })
1576 macro_rules! tuple {
1578 ( $($name:ident,)+ ) => (
1579 #[stable(feature = "rust1", since = "1.0.0")]
1580 impl<$($name:Debug),*> Debug for ($($name,)*) {
1581 #[allow(non_snake_case, unused_assignments, deprecated)]
1582 fn fmt(&self, f: &mut Formatter) -> Result {
1583 let mut builder = f.debug_tuple("");
1584 let ($(ref $name,)*) = *self;
1586 builder.field($name);
1592 peel! { $($name,)* }
1596 tuple! { T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, }
1598 #[stable(feature = "rust1", since = "1.0.0")]
1599 impl<T: Debug> Debug for [T] {
1600 fn fmt(&self, f: &mut Formatter) -> Result {
1601 f.debug_list().entries(self.iter()).finish()
1605 #[stable(feature = "rust1", since = "1.0.0")]
1607 fn fmt(&self, f: &mut Formatter) -> Result {
1611 #[stable(feature = "rust1", since = "1.0.0")]
1612 impl<T: ?Sized> Debug for PhantomData<T> {
1613 fn fmt(&self, f: &mut Formatter) -> Result {
1614 f.pad("PhantomData")
1618 #[stable(feature = "rust1", since = "1.0.0")]
1619 impl<T: Copy + Debug> Debug for Cell<T> {
1620 fn fmt(&self, f: &mut Formatter) -> Result {
1621 f.debug_struct("Cell")
1622 .field("value", &self.get())
1627 #[stable(feature = "rust1", since = "1.0.0")]
1628 impl<T: ?Sized + Debug> Debug for RefCell<T> {
1629 fn fmt(&self, f: &mut Formatter) -> Result {
1630 match self.borrow_state() {
1631 BorrowState::Unused | BorrowState::Reading => {
1632 f.debug_struct("RefCell")
1633 .field("value", &self.borrow())
1636 BorrowState::Writing => {
1637 f.debug_struct("RefCell")
1638 .field("value", &"<borrowed>")
1645 #[stable(feature = "rust1", since = "1.0.0")]
1646 impl<'b, T: ?Sized + Debug> Debug for Ref<'b, T> {
1647 fn fmt(&self, f: &mut Formatter) -> Result {
1648 Debug::fmt(&**self, f)
1652 #[stable(feature = "rust1", since = "1.0.0")]
1653 impl<'b, T: ?Sized + Debug> Debug for RefMut<'b, T> {
1654 fn fmt(&self, f: &mut Formatter) -> Result {
1655 Debug::fmt(&*(self.deref()), f)
1659 #[stable(feature = "core_impl_debug", since = "1.9.0")]
1660 impl<T: ?Sized + Debug> Debug for UnsafeCell<T> {
1661 fn fmt(&self, f: &mut Formatter) -> Result {
1666 // If you expected tests to be here, look instead at the run-pass/ifmt.rs test,
1667 // it's a lot easier than creating all of the rt::Piece structures here.