Module Printf

module Printf: sig  end

Formatted output functions.

val fprintf : Pervasives.out_channel -> ('a, Pervasives.out_channel, unit) format -> 'a

fprintf outchan format arg1 ... argN formats the arguments arg1 to argN according to the format string format, and outputs the resulting string on the channel outchan.

The format is a character string which contains two types of objects: plain characters, which are simply copied to the output channel, and conversion specifications, each of which causes conversion and printing of one argument.

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

• d or i: convert an integer argument to signed decimal.
• u: convert an integer argument to unsigned decimal.
• x: convert an integer argument to unsigned hexadecimal, using lowercase letters.
• X: convert an integer argument to unsigned hexadecimal, using uppercase letters.
• o: convert an integer argument to unsigned octal.
• s: insert a string argument.
• S: insert a string argument in Caml syntax (double quotes, escapes).
• c: insert a character argument.
• C: insert a character argument in Caml syntax (single quotes, escapes).
• f: convert a floating-point argument to decimal notation, in the style dddd.ddd.
• e or E: convert a floating-point argument to decimal notation, in the style d.ddd e+-dd (mantissa and exponent).
• g or G: convert a floating-point argument to decimal notation, in style f or e, E (whichever is more compact).
• b: convert a boolean argument to the string true or false
• ld, li, lu, lx, lX, lo: convert an int32 argument to the format specified by the second letter (decimal, hexadecimal, etc).
• nd, ni, nu, nx, nX, no: convert a nativeint argument to the format specified by the second letter.
• Ld, Li, Lu, Lx, LX, Lo: convert an int64 argument to the format specified by the second letter.
• a: user-defined printer. Takes two arguments and apply the first one to outchan (the current output channel) and to the second argument. The first argument must therefore have type out_channel -> 'b -> unit and the second 'b. The output produced by the function is therefore inserted in the output of fprintf at the current point.
• t: same as %a, but takes only one argument (with type out_channel -> unit) and apply it to outchan.
• %: take no argument and output one % character.

The optional flags include:

• -: left-justify the output (default is right justification).
• 0: for numerical conversions, pad with zeroes instead of spaces.
• +: for numerical conversions, prefix number with a + sign if positive.
• space: for numerical conversions, prefix number with a space if positive.
• #: request an alternate formatting style for numbers.

The field widths are composed of an optional integer literal indicating the minimal width of the result, possibly followed by a dot . and another integer literal indicating how many digits follow the decimal point in the %f, %e, and %E conversions. For instance, %6d prints an integer, prefixing it with spaces to fill at least 6 characters; and %.4f prints a float with 4 fractional digits. Each or both of the integer literals can also be specified as a *, in which case an extra integer argument is taken to specify the corresponding width or precision.

Warning: if too few arguments are provided, for instance because the printf function is partially applied, the format is immediately printed up to the conversion of the first missing argument; printing will then resume when the missing arguments are provided. For example, List.iter (printf "x=%d y=%d " 1) [2;3] prints x=1 y=2 3 instead of the expected x=1 y=2 x=1 y=3. To get the expected behavior, do List.iter (fun y -> printf "x=%d y=%d " 1 y) [2;3].

val printf : ('a, Pervasives.out_channel, unit) format -> 'a

Same as Printf.fprintf, but output on stdout.

val eprintf : ('a, Pervasives.out_channel, unit) format -> 'a

Same as Printf.fprintf, but output on stderr.

val sprintf : ('a, unit, string) format -> 'a

Same as Printf.fprintf, but instead of printing on an output channel, return a string containing the result of formatting the arguments.

val bprintf : Buffer.t -> ('a, Buffer.t, unit) format -> 'a

Same as Printf.fprintf, but instead of printing on an output channel, append the formatted arguments to the given extensible buffer (see module Buffer).

val kprintf : (string -> string) -> ('a, unit, string) format -> 'a

kprintf k format arguments is the same as sprintf format arguments, except that the resulting string is passed as argument to k; the result of k is then returned as the result of kprintf.