# Module Printf

    module Printf: sig .. end

Formatted output functions.

    val fprintf : out_channel ->
           ('a, 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`, `i`, `n`, or `N`: 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`.
- `F`: convert a floating-point argument in Caml syntax (`dddd.ddd` with a mandatory `.`).
- `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`
- `b`: convert a boolean argument (for backward compatibility; do not use in new programs).
- `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 flush the output.
- `%`: 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, out_channel, unit) format -> 'a

Same as `Printf.fprintf`, but output on `stdout`.

    val eprintf : ('a, 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 -> 'a) -> ('b, unit, string, 'a) format4 -> 'b

`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`.