19.23 | Module `Printf`: formatting printing 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 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
> `c`: insert a character argument
> `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`
> `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.
> Refer to the C library `printf` function for the meaning of flags and field width specifiers.
> If too few arguments are provided, printing stops just before converting the first missing argument.

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

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

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

> Same as `fprintf`, but output on `stderr`.

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

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