Scanf

bscanf ib format f reads tokens from the scanning buffer ib according to the format string format, converts these tokens to values, and applies the function f to these values. The result of this application of f is the result of the whole construct.

Raise Scanf.Scan_failure if the given input does not match the format.

Raise Failure if a conversion to a number is not possible.

Raise End_of_file if the end of input is encountered while scanning and the input matches the given format so far.

The format is a character string which contains three types of objects:

plain characters, which are simply matched with the characters of the input,
conversion specifications, each of which causes reading and conversion of one argument for f,
scanning indications to specify boundaries of tokens.

Among plain characters the space character (ASCII code 32) has a special meaning: it matches ``whitespace'', that is any number of tab, space, newline and carriage return characters. Hence, a space in the format matches any amount of whitespace in the input.

Conversion specifications consist in the % character, followed by optional field width, followed by one or two conversion characters. The conversion characters and their meanings are:

d: reads an optionally signed decimal integer.
i: reads an optionally signed integer (usual input formats for hexadecimal (0x[d]+ and 0X[d]+), octal (0o[d]+), and binary 0b[d]+ notations are understood).
u: reads an unsigned decimal integer.
x or X: reads an unsigned hexadecimal integer.
o: reads an unsigned octal integer.
s: reads a string argument (by default strings end with a space).
S: reads a delimited string argument (delimiters and special escaped characters follow the lexical conventions of Caml).
c: reads a single character.
C: reads a single delimited character (delimiters and special escaped characters follow the lexical conventions of Caml).
f, e, E, g, G: reads an optionally signed floating-point number in decimal notation, in the style dddd.ddd e/E+-dd.
b: reads a boolean argument (true or false).
ld, li, lu, lx, lX, lo: reads an int32 argument to the format specified by the second letter (decimal, hexadecimal, etc).
nd, ni, nu, nx, nX, no: reads a nativeint argument to the format specified by the second letter.
Ld, Li, Lu, Lx, LX, Lo: reads an int64 argument to the format specified by the second letter.
[ range ]: reads characters that matches one of the characters mentioned in the range of characters range (or not mentioned in it, if the range starts with ^). Returns a string that can be empty, if no character in the input matches the range.
N: applies f to the number of characters read so far.
%: matches one % character in the input.

The field widths are composed of an optional integer literal indicating the maximal width of the token to read. For instance, %6d reads an integer, having at most 6 decimal digits; and %4f reads a float with 4 characters.

Scanning indications appear just after string conversions s and [ range ] to delimit the end of the token. A scanning indication is introduced by a @ character, followed by some constant character c. It means that the string token should end just before the next matching c. If no c character is encountered, the string token spreads as much as possible. For instance, "%s@\t" reads a string up to the next tabulation character. If a scanning indication @c does not follow a string conversion, it is ignored and treated as a plain c character.

Note: the scanf facility is not intended for heavy duty lexical analysis and parsing. If it appears not expressive enough for your needs, several alternative exists: regular expressions (module Str), stream parsers, ocamllex-generated lexers, ocamlyacc-generated parsers.

Module Scanf