286 lines
14 KiB
OCaml
286 lines
14 KiB
OCaml
(***********************************************************************)
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(* *)
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(* Objective Caml *)
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(* *)
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(* Pierre Weis, projet Cristal, INRIA Rocquencourt *)
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(* *)
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(* Copyright 2002 Institut National de Recherche en Informatique et *)
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(* en Automatique. All rights reserved. This file is distributed *)
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(* under the terms of the GNU Library General Public License, with *)
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(* the special exception on linking described in file ../LICENSE. *)
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(* *)
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(***********************************************************************)
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(* $Id$ *)
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(** Formatted input functions. *)
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(** Scanning buffers. *)
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module Scanning : sig
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type scanbuf;;
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(** The type of scanning buffers. A scanning buffer is the argument passed
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to the scanning functions used by the [scanf] family of functions.
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The scanning buffer holds the current state of the scan, plus
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a function to get the next char from the input, and a token buffer
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to store the string matched so far.
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Note: a scan may often require to examine one character in advance;
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when this ``lookahead'' character does not belong to the token read,
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it is stored back in the scanning buffer and becomes the next
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character read. *)
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val stdib : scanbuf;;
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(** The scanning buffer reading from [stdin].
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[stdib] is equivalent to [Scanning.from_channel stdin].
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Note: when input is read interactively from [stdin], the carriage return
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that triggers the evaluation is incoporated in the input; thus, scanning
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specifications must properly skip this character (simply add a space
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as the last character of the format string). *)
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val from_string : string -> scanbuf;;
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(** [Scanning.from_string s] returns a scanning buffer which reads
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from the given string.
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Reading starts from the first character in the string.
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The end-of-input condition is set when the end of the string is reached. *)
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val from_file : string -> scanbuf;;
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(** Bufferized file reading in text mode. The efficient and usual
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way to scan text mode files (in effect, [from_file] returns a
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buffer that reads characters in large chunks, rather than one
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character at a time as buffers returned by [from_channel] do).
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[Scanning.from_file fname] returns a scanning buffer which reads
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from the given file [fname] in text mode. *)
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val from_file_bin : string -> scanbuf;;
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(** Bufferized file reading in binary mode. *)
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val from_function : (unit -> char) -> scanbuf;;
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(** [Scanning.from_function f] returns a scanning buffer with
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the given function as its reading method.
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When scanning needs one more character, the given function is called.
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When the function has no more character to provide, it must signal
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an end-of-input condition by raising the exception [End_of_file]. *)
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val from_channel : in_channel -> scanbuf;;
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(** [Scanning.from_channel ic] returns a scanning buffer which reads
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one character at a time from the input channel [ic], starting at the
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current reading position. *)
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val end_of_input : scanbuf -> bool;;
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(** [Scanning.end_of_input ib] tests the end-of-input condition
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of the given buffer. *)
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val beginning_of_input : scanbuf -> bool;;
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(** [Scanning.beginning_of_input ib] tests the beginning of input
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condition of the given buffer. *)
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val name_of_input : scanbuf -> string;;
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(** [Scanning.file_name_of_input ib] returns the name of the character
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source for the input buffer [ib]. *)
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end;;
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exception Scan_failure of string;;
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(** The exception that formatted input functions raise when the input
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cannot be read according to the given format. *)
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val bscanf :
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Scanning.scanbuf -> ('a, Scanning.scanbuf, 'b) format -> 'a -> 'b;;
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(** [bscanf ib fmt f] reads tokens from the scanning buffer [ib] according
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to the format string [fmt], converts these tokens to values, and
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applies the function [f] to these values.
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The result of this application of [f] is the result of the whole construct.
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For instance, if [p] is the function [fun s i -> i + 1], then
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[Scanf.sscanf "x = 1" "%s = %i" p] returns [2].
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The format is a character string which contains three types of
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objects:
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- plain characters, which are simply matched with the
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characters of the input,
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- conversion specifications, each of which causes reading and
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conversion of one argument for [f],
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- scanning indications to specify boundaries of tokens.
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Among plain characters the space character (ASCII code 32) has a
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special meaning: it matches ``whitespace'', that is any number of tab,
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space, newline and carriage return characters. Hence, a space in the format
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matches any amount of whitespace in the input.
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Conversion specifications consist in the [%] character, followed by
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an optional flag, an optional field width, and followed by one or
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two conversion characters. The conversion characters and their
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meanings are:
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- [d]: reads an optionally signed decimal integer.
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- [i]: reads an optionally signed integer
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(usual input formats for hexadecimal ([0x[d]+] and [0X[d]+]),
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octal ([0o[d]+]), and binary [0b[d]+] notations are understood).
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- [u]: reads an unsigned decimal integer.
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- [x] or [X]: reads an unsigned hexadecimal integer.
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- [o]: reads an unsigned octal integer.
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- [s]: reads a string argument that spreads as much as possible,
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until the next white space, the next scanning indication, or the
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end-of-input is reached. Hence, this conversion always succeeds:
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it returns an empty string if the bounding condition holds
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when the scan begins.
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- [S]: reads a delimited string argument (delimiters and special
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escaped characters follow the lexical conventions of Caml).
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- [c]: reads a single character. To test the current input character
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without reading it, specify a null field width, i.e. use
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specification [%0c]. Raise [Invalid_argument], if the field width
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specification is greater than 1.
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- [C]: reads a single delimited character (delimiters and special
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escaped characters follow the lexical conventions of Caml).
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- [f], [e], [E], [g], [G]: reads an optionally signed
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floating-point number in decimal notation, in the style [dddd.ddd
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e/E+-dd].
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- [F]: reads a floating point number according to the lexical
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conventions of Caml (hence the decimal point is mandatory if the
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exponent part is not mentioned).
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- [B]: reads a boolean argument ([true] or [false]).
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- [b]: reads a boolean argument (for backward compatibility; do not use
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in new programs).
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- [ld], [li], [lu], [lx], [lX], [lo]: reads an [int32] argument to
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the format specified by the second letter (decimal, hexadecimal, etc).
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- [nd], [ni], [nu], [nx], [nX], [no]: reads a [nativeint] argument to
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the format specified by the second letter.
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- [Ld], [Li], [Lu], [Lx], [LX], [Lo]: reads an [int64] argument to
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the format specified by the second letter.
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- [\[ range \]]: reads characters that matches one of the characters
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mentioned in the range of characters [range] (or not mentioned in
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it, if the range starts with [^]). Reads a [string] that can be
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empty, if no character in the input matches the range. The set of
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characters from [c1] to [c2] (inclusively) is denoted by [c1-c2].
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Hence, [%\[0-9\]] returns a string representing a decimal number
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or an empty string if no decimal digit is found; similarly,
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[%\[\\048-\\057\\065-\\070\]] returns a string of hexadecimal digits.
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If a closing bracket appears in a range, it must occur as the
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first character of the range (or just after the [^] in case of
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range negation); hence [\[\]\]] matches a [\]] character and
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[\[^\]\]] matches any character that is not [\]].
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- [\{ fmt %\}]: reads a format string argument to the format
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specified by the internal format [fmt]. The format string to be
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read must have the same type as the internal format [fmt].
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For instance, "%\{%i%\}" reads any format string that can read a value of
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type [int]; hence [Scanf.sscanf "fmt:\\\"number is %u\\\"" "fmt:%\{%i%\}"]
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succeeds and returns the format string ["number is %u"].
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- [\( fmt %\)]: scanning format substitution.
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Reads a format string to replace [fmt]. The format string read
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must have the same type as [fmt].
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- [l]: applies [f] to the number of lines read so far.
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- [n]: applies [f] to the number of characters read so far.
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- [N] or [L]: applies [f] to the number of tokens read so far.
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- [!]: matches the end of input condition.
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- [%]: matches one [%] character in the input.
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Following the [%] character introducing a conversion, there may be
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the special flag [_]: the conversion that follows occurs as usual,
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but the resulting value is discarded.
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The field widths are composed of an optional integer literal
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indicating the maximal width of the token to read.
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For instance, [%6d] reads an integer, having at most 6 decimal digits;
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[%4f] reads a float with at most 4 characters; and [%8\[\\000-\\255\]]
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returns the next 8 characters (or all the characters still available,
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if less than 8 characters are available in the input).
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Scanning indications appear just after the string conversions [s]
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and [\[ range \]] to delimit the end of the token. A scanning
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indication is introduced by a [@] character, followed by some
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constant character [c]. It means that the string token should end
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just before the next matching [c] (which is skipped). If no [c]
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character is encountered, the string token spreads as much as
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possible. For instance, ["%s@\t"] reads a string up to the next
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tabulation character or to the end of input. If a scanning
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indication [\@c] does not follow a string conversion, it is treated
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as a plain [c] character.
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Raise [Scanf.Scan_failure] if the given input does not match the format.
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Raise [Failure] if a conversion to a number is not possible.
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Raise [End_of_file] if the end of input is encountered while some
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more characters are needed to read the current conversion
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specification (this means in particular that scanning a [%s]
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conversion never raises exception [End_of_file]: if the end of
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input is reached the conversion succeeds and simply returns [""]).
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Notes:
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- the scanning indications introduce slight differences in the
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syntax of [Scanf] format strings compared to those used by the
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[Printf] module. However, scanning indications are similar to those
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of the [Format] module; hence, when producing formatted text to be
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scanned by [!Scanf.bscanf], it is wise to use printing functions
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from [Format] (or, if you need to use functions from [Printf],
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banish or carefully double check the format strings that contain
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['\@'] characters).
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- in addition to relevant digits, ['_'] characters may appear
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inside numbers (this is reminiscent to the usual Caml
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conventions). If stricter scanning is desired, use the range
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conversion facility instead of the number conversions.
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- the [scanf] facility is not intended for heavy duty lexical
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analysis and parsing. If it appears not expressive enough for your
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needs, several alternative exists: regular expressions (module
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[Str]), stream parsers, [ocamllex]-generated lexers,
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[ocamlyacc]-generated parsers.
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*)
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val fscanf : in_channel -> ('a, Scanning.scanbuf, 'b) format -> 'a -> 'b;;
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(** Same as {!Scanf.bscanf}, but inputs from the given channel.
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Warning: since all scanning functions operate from a scanning
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buffer, be aware that each [fscanf] invocation must allocate a new
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fresh scanning buffer (unless careful use of partial evaluation in
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the program). Hence, there are chances that some characters seem
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to be skipped (in fact they are pending in the previously used
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buffer). This happens in particular when calling [fscanf] again
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after a scan involving a format that necessitates some look ahead
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(such as a format that ends by skipping whitespace in the input).
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To avoid confusion, consider using [bscanf] with an explicitly
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created scanning buffer. Use for instance [Scanning.from_file f]
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to allocate the scanning buffer reading from file [f].
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This method is not only clearer it is also faster, since scanning
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buffers to files are optimized for fast bufferized reading. *)
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val sscanf : string -> ('a, Scanning.scanbuf, 'b) format -> 'a -> 'b;;
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(** Same as {!Scanf.bscanf}, but inputs from the given string. *)
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val scanf : ('a, Scanning.scanbuf, 'b) format -> 'a -> 'b;;
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(** Same as {!Scanf.bscanf}, but reads from the predefined scanning
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buffer {!Scanf.Scanning.stdib} that is connected to [stdin]. *)
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val kscanf :
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Scanning.scanbuf -> (Scanning.scanbuf -> exn -> 'a) ->
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('b, Scanning.scanbuf, 'a) format -> 'b -> 'a;;
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(** Same as {!Scanf.bscanf}, but takes an additional function argument
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[ef] that is called in case of error: if the scanning process or
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some conversion fails, the scanning function aborts and applies the
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error handling function [ef] to the scanning buffer and the
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exception that aborted the scanning process. *)
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val bscanf_format :
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Scanning.scanbuf -> ('a, 'b, 'c, 'd) format4 ->
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(('a, 'b, 'c, 'd) format4 -> 'e) -> 'e;;
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(** [bscanf_format ib fmt f] reads a format string token in buffer [ib],
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according to the format string [fmt], and applies the function [f] to the
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resulting format string value.
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Raises [Scan_failure] if the format string value read has not the same type
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as [fmt]. *)
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val sscanf_format :
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string -> ('a, 'b, 'c, 'd) format4 ->
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(('a, 'b, 'c, 'd) format4 -> 'e) -> 'e;;
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(** Same as {!Scanf.bscanf}, but inputs from the given string. *)
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val format_from_string :
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string -> ('a, 'b, 'c, 'd) format4 -> ('a, 'b, 'c, 'd) format4;;
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(** Same as {!Scanf.sscanf_format}, but converts the given string to a format
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string. *)
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