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 if let Some(max) = self.precision {
985 // If there's a maximum width and our string is longer than
986 // that, then we must always have truncation. This is the only
987 // case where the maximum length will matter.
988 if let Some((i, _)) = s.char_indices().skip(max).next() {
989 return self.buf.write_str(&s[..i])
992 // The `width` field is more of a `min-width` parameter at this point.
994 // If we're under the maximum length, and there's no minimum length
995 // requirements, then we can just emit the string
996 None => self.buf.write_str(s),
997 // If we're under the maximum width, check if we're over the minimum
998 // width, if so it's as easy as just emitting the string.
999 Some(width) if s.chars().count() >= width => {
1000 self.buf.write_str(s)
1002 // If we're under both the maximum and the minimum width, then fill
1003 // up the minimum width with the specified string + some alignment.
1005 let align = rt::v1::Alignment::Left;
1006 self.with_padding(width - s.chars().count(), align, |me| {
1013 /// Runs a callback, emitting the correct padding either before or
1014 /// afterwards depending on whether right or left alignment is requested.
1015 fn with_padding<F>(&mut self, padding: usize, default: rt::v1::Alignment,
1017 where F: FnOnce(&mut Formatter) -> Result,
1020 let align = match self.align {
1021 rt::v1::Alignment::Unknown => default,
1025 let (pre_pad, post_pad) = match align {
1026 rt::v1::Alignment::Left => (0, padding),
1027 rt::v1::Alignment::Right |
1028 rt::v1::Alignment::Unknown => (padding, 0),
1029 rt::v1::Alignment::Center => (padding / 2, (padding + 1) / 2),
1032 let fill = self.fill.encode_utf8();
1034 str::from_utf8_unchecked(fill.as_slice())
1037 for _ in 0..pre_pad {
1038 self.buf.write_str(fill)?;
1043 for _ in 0..post_pad {
1044 self.buf.write_str(fill)?;
1050 /// Takes the formatted parts and applies the padding.
1051 /// Assumes that the caller already has rendered the parts with required precision,
1052 /// so that `self.precision` can be ignored.
1053 fn pad_formatted_parts(&mut self, formatted: &flt2dec::Formatted) -> Result {
1054 if let Some(mut width) = self.width {
1055 // for the sign-aware zero padding, we render the sign first and
1056 // behave as if we had no sign from the beginning.
1057 let mut formatted = formatted.clone();
1058 let mut align = self.align;
1059 let old_fill = self.fill;
1060 if self.sign_aware_zero_pad() {
1061 // a sign always goes first
1062 let sign = unsafe { str::from_utf8_unchecked(formatted.sign) };
1063 self.buf.write_str(sign)?;
1065 // remove the sign from the formatted parts
1066 formatted.sign = b"";
1067 width = if width < sign.len() { 0 } else { width - sign.len() };
1068 align = rt::v1::Alignment::Right;
1072 // remaining parts go through the ordinary padding process.
1073 let len = formatted.len();
1074 let ret = if width <= len { // no padding
1075 self.write_formatted_parts(&formatted)
1077 self.with_padding(width - len, align, |f| {
1078 f.write_formatted_parts(&formatted)
1081 self.fill = old_fill;
1084 // this is the common case and we take a shortcut
1085 self.write_formatted_parts(formatted)
1089 fn write_formatted_parts(&mut self, formatted: &flt2dec::Formatted) -> Result {
1090 fn write_bytes(buf: &mut Write, s: &[u8]) -> Result {
1091 buf.write_str(unsafe { str::from_utf8_unchecked(s) })
1094 if !formatted.sign.is_empty() {
1095 write_bytes(self.buf, formatted.sign)?;
1097 for part in formatted.parts {
1099 flt2dec::Part::Zero(mut nzeroes) => {
1100 const ZEROES: &'static str = // 64 zeroes
1101 "0000000000000000000000000000000000000000000000000000000000000000";
1102 while nzeroes > ZEROES.len() {
1103 self.buf.write_str(ZEROES)?;
1104 nzeroes -= ZEROES.len();
1107 self.buf.write_str(&ZEROES[..nzeroes])?;
1110 flt2dec::Part::Num(mut v) => {
1112 let len = part.len();
1113 for c in s[..len].iter_mut().rev() {
1114 *c = b'0' + (v % 10) as u8;
1117 write_bytes(self.buf, &s[..len])?;
1119 flt2dec::Part::Copy(buf) => {
1120 write_bytes(self.buf, buf)?;
1127 /// Writes some data to the underlying buffer contained within this
1129 #[stable(feature = "rust1", since = "1.0.0")]
1130 pub fn write_str(&mut self, data: &str) -> Result {
1131 self.buf.write_str(data)
1134 /// Writes some formatted information into this instance
1135 #[stable(feature = "rust1", since = "1.0.0")]
1136 pub fn write_fmt(&mut self, fmt: Arguments) -> Result {
1137 write(self.buf, fmt)
1140 /// Flags for formatting (packed version of rt::Flag)
1141 #[stable(feature = "rust1", since = "1.0.0")]
1142 pub fn flags(&self) -> u32 { self.flags }
1144 /// Character used as 'fill' whenever there is alignment
1145 #[stable(feature = "fmt_flags", since = "1.5.0")]
1146 pub fn fill(&self) -> char { self.fill }
1148 /// Flag indicating what form of alignment was requested
1149 #[unstable(feature = "fmt_flags_align", reason = "method was just created",
1151 pub fn align(&self) -> Alignment {
1153 rt::v1::Alignment::Left => Alignment::Left,
1154 rt::v1::Alignment::Right => Alignment::Right,
1155 rt::v1::Alignment::Center => Alignment::Center,
1156 rt::v1::Alignment::Unknown => Alignment::Unknown,
1160 /// Optionally specified integer width that the output should be
1161 #[stable(feature = "fmt_flags", since = "1.5.0")]
1162 pub fn width(&self) -> Option<usize> { self.width }
1164 /// Optionally specified precision for numeric types
1165 #[stable(feature = "fmt_flags", since = "1.5.0")]
1166 pub fn precision(&self) -> Option<usize> { self.precision }
1168 /// Determines if the `+` flag was specified.
1169 #[stable(feature = "fmt_flags", since = "1.5.0")]
1170 pub fn sign_plus(&self) -> bool { self.flags & (1 << FlagV1::SignPlus as u32) != 0 }
1172 /// Determines if the `-` flag was specified.
1173 #[stable(feature = "fmt_flags", since = "1.5.0")]
1174 pub fn sign_minus(&self) -> bool { self.flags & (1 << FlagV1::SignMinus as u32) != 0 }
1176 /// Determines if the `#` flag was specified.
1177 #[stable(feature = "fmt_flags", since = "1.5.0")]
1178 pub fn alternate(&self) -> bool { self.flags & (1 << FlagV1::Alternate as u32) != 0 }
1180 /// Determines if the `0` flag was specified.
1181 #[stable(feature = "fmt_flags", since = "1.5.0")]
1182 pub fn sign_aware_zero_pad(&self) -> bool {
1183 self.flags & (1 << FlagV1::SignAwareZeroPad as u32) != 0
1186 /// Creates a `DebugStruct` builder designed to assist with creation of
1187 /// `fmt::Debug` implementations for structs.
1199 /// impl fmt::Debug for Foo {
1200 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
1201 /// fmt.debug_struct("Foo")
1202 /// .field("bar", &self.bar)
1203 /// .field("baz", &self.baz)
1208 /// // prints "Foo { bar: 10, baz: "Hello World" }"
1209 /// println!("{:?}", Foo { bar: 10, baz: "Hello World".to_string() });
1211 #[stable(feature = "debug_builders", since = "1.2.0")]
1213 pub fn debug_struct<'b>(&'b mut self, name: &str) -> DebugStruct<'b, 'a> {
1214 builders::debug_struct_new(self, name)
1217 /// Creates a `DebugTuple` builder designed to assist with creation of
1218 /// `fmt::Debug` implementations for tuple structs.
1225 /// struct Foo(i32, String);
1227 /// impl fmt::Debug for Foo {
1228 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
1229 /// fmt.debug_tuple("Foo")
1236 /// // prints "Foo(10, "Hello World")"
1237 /// println!("{:?}", Foo(10, "Hello World".to_string()));
1239 #[stable(feature = "debug_builders", since = "1.2.0")]
1241 pub fn debug_tuple<'b>(&'b mut self, name: &str) -> DebugTuple<'b, 'a> {
1242 builders::debug_tuple_new(self, name)
1245 /// Creates a `DebugList` builder designed to assist with creation of
1246 /// `fmt::Debug` implementations for list-like structures.
1253 /// struct Foo(Vec<i32>);
1255 /// impl fmt::Debug for Foo {
1256 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
1257 /// fmt.debug_list().entries(self.0.iter()).finish()
1261 /// // prints "[10, 11]"
1262 /// println!("{:?}", Foo(vec![10, 11]));
1264 #[stable(feature = "debug_builders", since = "1.2.0")]
1266 pub fn debug_list<'b>(&'b mut self) -> DebugList<'b, 'a> {
1267 builders::debug_list_new(self)
1270 /// Creates a `DebugSet` builder designed to assist with creation of
1271 /// `fmt::Debug` implementations for set-like structures.
1278 /// struct Foo(Vec<i32>);
1280 /// impl fmt::Debug for Foo {
1281 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
1282 /// fmt.debug_set().entries(self.0.iter()).finish()
1286 /// // prints "{10, 11}"
1287 /// println!("{:?}", Foo(vec![10, 11]));
1289 #[stable(feature = "debug_builders", since = "1.2.0")]
1291 pub fn debug_set<'b>(&'b mut self) -> DebugSet<'b, 'a> {
1292 builders::debug_set_new(self)
1295 /// Creates a `DebugMap` builder designed to assist with creation of
1296 /// `fmt::Debug` implementations for map-like structures.
1303 /// struct Foo(Vec<(String, i32)>);
1305 /// impl fmt::Debug for Foo {
1306 /// fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
1307 /// fmt.debug_map().entries(self.0.iter().map(|&(ref k, ref v)| (k, v))).finish()
1311 /// // prints "{"A": 10, "B": 11}"
1312 /// println!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)]));
1314 #[stable(feature = "debug_builders", since = "1.2.0")]
1316 pub fn debug_map<'b>(&'b mut self) -> DebugMap<'b, 'a> {
1317 builders::debug_map_new(self)
1321 #[stable(since = "1.2.0", feature = "formatter_write")]
1322 impl<'a> Write for Formatter<'a> {
1323 fn write_str(&mut self, s: &str) -> Result {
1324 self.buf.write_str(s)
1327 fn write_char(&mut self, c: char) -> Result {
1328 self.buf.write_char(c)
1331 fn write_fmt(&mut self, args: Arguments) -> Result {
1332 write(self.buf, args)
1336 #[stable(feature = "rust1", since = "1.0.0")]
1337 impl Display for Error {
1338 fn fmt(&self, f: &mut Formatter) -> Result {
1339 Display::fmt("an error occurred when formatting an argument", f)
1343 // Implementations of the core formatting traits
1345 macro_rules! fmt_refs {
1346 ($($tr:ident),*) => {
1348 #[stable(feature = "rust1", since = "1.0.0")]
1349 impl<'a, T: ?Sized + $tr> $tr for &'a T {
1350 fn fmt(&self, f: &mut Formatter) -> Result { $tr::fmt(&**self, f) }
1352 #[stable(feature = "rust1", since = "1.0.0")]
1353 impl<'a, T: ?Sized + $tr> $tr for &'a mut T {
1354 fn fmt(&self, f: &mut Formatter) -> Result { $tr::fmt(&**self, f) }
1360 fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp }
1362 #[stable(feature = "rust1", since = "1.0.0")]
1363 impl Debug for bool {
1364 fn fmt(&self, f: &mut Formatter) -> Result {
1365 Display::fmt(self, f)
1369 #[stable(feature = "rust1", since = "1.0.0")]
1370 impl Display for bool {
1371 fn fmt(&self, f: &mut Formatter) -> Result {
1372 Display::fmt(if *self { "true" } else { "false" }, f)
1376 #[stable(feature = "rust1", since = "1.0.0")]
1377 impl Debug for str {
1378 fn fmt(&self, f: &mut Formatter) -> Result {
1381 for (i, c) in self.char_indices() {
1382 let esc = c.escape_default();
1383 // If char needs escaping, flush backlog so far and write, else skip
1385 f.write_str(&self[from..i])?;
1389 from = i + c.len_utf8();
1392 f.write_str(&self[from..])?;
1397 #[stable(feature = "rust1", since = "1.0.0")]
1398 impl Display for str {
1399 fn fmt(&self, f: &mut Formatter) -> Result {
1404 #[stable(feature = "rust1", since = "1.0.0")]
1405 impl Debug for char {
1406 fn fmt(&self, f: &mut Formatter) -> Result {
1407 f.write_char('\'')?;
1408 for c in self.escape_default() {
1415 #[stable(feature = "rust1", since = "1.0.0")]
1416 impl Display for char {
1417 fn fmt(&self, f: &mut Formatter) -> Result {
1418 if f.width.is_none() && f.precision.is_none() {
1422 str::from_utf8_unchecked(self.encode_utf8().as_slice())
1428 #[stable(feature = "rust1", since = "1.0.0")]
1429 impl<T: ?Sized> Pointer for *const T {
1430 fn fmt(&self, f: &mut Formatter) -> Result {
1431 let old_width = f.width;
1432 let old_flags = f.flags;
1434 // The alternate flag is already treated by LowerHex as being special-
1435 // it denotes whether to prefix with 0x. We use it to work out whether
1436 // or not to zero extend, and then unconditionally set it to get the
1439 f.flags |= 1 << (FlagV1::SignAwareZeroPad as u32);
1441 if let None = f.width {
1442 f.width = Some(((mem::size_of::<usize>() * 8) / 4) + 2);
1445 f.flags |= 1 << (FlagV1::Alternate as u32);
1447 let ret = LowerHex::fmt(&(*self as *const () as usize), f);
1449 f.width = old_width;
1450 f.flags = old_flags;
1456 #[stable(feature = "rust1", since = "1.0.0")]
1457 impl<T: ?Sized> Pointer for *mut T {
1458 fn fmt(&self, f: &mut Formatter) -> Result {
1459 Pointer::fmt(&(*self as *const T), f)
1463 #[stable(feature = "rust1", since = "1.0.0")]
1464 impl<'a, T: ?Sized> Pointer for &'a T {
1465 fn fmt(&self, f: &mut Formatter) -> Result {
1466 Pointer::fmt(&(*self as *const T), f)
1470 #[stable(feature = "rust1", since = "1.0.0")]
1471 impl<'a, T: ?Sized> Pointer for &'a mut T {
1472 fn fmt(&self, f: &mut Formatter) -> Result {
1473 Pointer::fmt(&(&**self as *const T), f)
1477 // Common code of floating point Debug and Display.
1478 fn float_to_decimal_common<T>(fmt: &mut Formatter, num: &T, negative_zero: bool) -> Result
1479 where T: flt2dec::DecodableFloat
1481 let force_sign = fmt.sign_plus();
1482 let sign = match (force_sign, negative_zero) {
1483 (false, false) => flt2dec::Sign::Minus,
1484 (false, true) => flt2dec::Sign::MinusRaw,
1485 (true, false) => flt2dec::Sign::MinusPlus,
1486 (true, true) => flt2dec::Sign::MinusPlusRaw,
1489 let mut buf = [0; 1024]; // enough for f32 and f64
1490 let mut parts = [flt2dec::Part::Zero(0); 16];
1491 let formatted = if let Some(precision) = fmt.precision {
1492 flt2dec::to_exact_fixed_str(flt2dec::strategy::grisu::format_exact, *num, sign,
1493 precision, false, &mut buf, &mut parts)
1495 flt2dec::to_shortest_str(flt2dec::strategy::grisu::format_shortest, *num, sign,
1496 0, false, &mut buf, &mut parts)
1498 fmt.pad_formatted_parts(&formatted)
1501 // Common code of floating point LowerExp and UpperExp.
1502 fn float_to_exponential_common<T>(fmt: &mut Formatter, num: &T, upper: bool) -> Result
1503 where T: flt2dec::DecodableFloat
1505 let force_sign = fmt.sign_plus();
1506 let sign = match force_sign {
1507 false => flt2dec::Sign::Minus,
1508 true => flt2dec::Sign::MinusPlus,
1511 let mut buf = [0; 1024]; // enough for f32 and f64
1512 let mut parts = [flt2dec::Part::Zero(0); 16];
1513 let formatted = if let Some(precision) = fmt.precision {
1514 // 1 integral digit + `precision` fractional digits = `precision + 1` total digits
1515 flt2dec::to_exact_exp_str(flt2dec::strategy::grisu::format_exact, *num, sign,
1516 precision + 1, upper, &mut buf, &mut parts)
1518 flt2dec::to_shortest_exp_str(flt2dec::strategy::grisu::format_shortest, *num, sign,
1519 (0, 0), upper, &mut buf, &mut parts)
1521 fmt.pad_formatted_parts(&formatted)
1524 macro_rules! floating { ($ty:ident) => {
1526 #[stable(feature = "rust1", since = "1.0.0")]
1527 impl Debug for $ty {
1528 fn fmt(&self, fmt: &mut Formatter) -> Result {
1529 float_to_decimal_common(fmt, self, true)
1533 #[stable(feature = "rust1", since = "1.0.0")]
1534 impl Display for $ty {
1535 fn fmt(&self, fmt: &mut Formatter) -> Result {
1536 float_to_decimal_common(fmt, self, false)
1540 #[stable(feature = "rust1", since = "1.0.0")]
1541 impl LowerExp for $ty {
1542 fn fmt(&self, fmt: &mut Formatter) -> Result {
1543 float_to_exponential_common(fmt, self, false)
1547 #[stable(feature = "rust1", since = "1.0.0")]
1548 impl UpperExp for $ty {
1549 fn fmt(&self, fmt: &mut Formatter) -> Result {
1550 float_to_exponential_common(fmt, self, true)
1557 // Implementation of Display/Debug for various core types
1559 #[stable(feature = "rust1", since = "1.0.0")]
1560 impl<T> Debug for *const T {
1561 fn fmt(&self, f: &mut Formatter) -> Result { Pointer::fmt(self, f) }
1563 #[stable(feature = "rust1", since = "1.0.0")]
1564 impl<T> Debug for *mut T {
1565 fn fmt(&self, f: &mut Formatter) -> Result { Pointer::fmt(self, f) }
1569 ($name:ident, $($other:ident,)*) => (tuple! { $($other,)* })
1572 macro_rules! tuple {
1574 ( $($name:ident,)+ ) => (
1575 #[stable(feature = "rust1", since = "1.0.0")]
1576 impl<$($name:Debug),*> Debug for ($($name,)*) {
1577 #[allow(non_snake_case, unused_assignments, deprecated)]
1578 fn fmt(&self, f: &mut Formatter) -> Result {
1579 let mut builder = f.debug_tuple("");
1580 let ($(ref $name,)*) = *self;
1582 builder.field($name);
1588 peel! { $($name,)* }
1592 tuple! { T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, }
1594 #[stable(feature = "rust1", since = "1.0.0")]
1595 impl<T: Debug> Debug for [T] {
1596 fn fmt(&self, f: &mut Formatter) -> Result {
1597 f.debug_list().entries(self.iter()).finish()
1601 #[stable(feature = "rust1", since = "1.0.0")]
1603 fn fmt(&self, f: &mut Formatter) -> Result {
1607 #[stable(feature = "rust1", since = "1.0.0")]
1608 impl<T: ?Sized> Debug for PhantomData<T> {
1609 fn fmt(&self, f: &mut Formatter) -> Result {
1610 f.pad("PhantomData")
1614 #[stable(feature = "rust1", since = "1.0.0")]
1615 impl<T: Copy + Debug> Debug for Cell<T> {
1616 fn fmt(&self, f: &mut Formatter) -> Result {
1617 f.debug_struct("Cell")
1618 .field("value", &self.get())
1623 #[stable(feature = "rust1", since = "1.0.0")]
1624 impl<T: ?Sized + Debug> Debug for RefCell<T> {
1625 fn fmt(&self, f: &mut Formatter) -> Result {
1626 match self.borrow_state() {
1627 BorrowState::Unused | BorrowState::Reading => {
1628 f.debug_struct("RefCell")
1629 .field("value", &self.borrow())
1632 BorrowState::Writing => {
1633 f.debug_struct("RefCell")
1634 .field("value", &"<borrowed>")
1641 #[stable(feature = "rust1", since = "1.0.0")]
1642 impl<'b, T: ?Sized + Debug> Debug for Ref<'b, T> {
1643 fn fmt(&self, f: &mut Formatter) -> Result {
1644 Debug::fmt(&**self, f)
1648 #[stable(feature = "rust1", since = "1.0.0")]
1649 impl<'b, T: ?Sized + Debug> Debug for RefMut<'b, T> {
1650 fn fmt(&self, f: &mut Formatter) -> Result {
1651 Debug::fmt(&*(self.deref()), f)
1655 #[stable(feature = "core_impl_debug", since = "1.9.0")]
1656 impl<T: ?Sized + Debug> Debug for UnsafeCell<T> {
1657 fn fmt(&self, f: &mut Formatter) -> Result {
1662 // If you expected tests to be here, look instead at the run-pass/ifmt.rs test,
1663 // it's a lot easier than creating all of the rt::Piece structures here.