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string/format

core-api



    cfunction
    src/core/string.c on line 536, column 1

    (string/format format & values)

    Similar to C's `snprintf`, but specialized for operating with Janet 
    values. Returns a new string.

    The following conversion specifiers are supported, where the upper 
    case specifiers generate upper case output:

     $*$  `c`: ASCII character.
     $*$  `d`, `i`: integer, formatted as a decimal number.
     $*$  `x`, `X`: integer, formatted as a hexadecimal number.
     $*$  `o`: integer, formatted as an octal number.
     $*$  `f`, `F`: floating point number, formatted as a decimal number.
     $*$  `e`, `E`: floating point number, formatted in scientific 
      notation.
     $*$  `g`, `G`: floating point number, formatted in its shortest form.
     $*$  `a`, `A`: floating point number, formatted as a hexadecimal 
      number.
     $*$  `s`: formatted as a string, precision indicates padding and 
      maximum length.
     $*$  `t`: emit the type of the given value.
     $*$  `v`: format with (describe x)
     $*$  `V`: format with (string x)
     $*$  `j`: format to jdn (Janet data notation).

    The following conversion specifiers are used for "pretty-printing", 
    where the upper-case variants generate colored output. These 
    specifiers can take a precision argument to specify the maximum 
    nesting depth to print.

     $*$  `p`, `P`: pretty format, truncating if necessary
     $*$  `m`, `M`: pretty format without truncating.
     $*$  `q`, `Q`: pretty format on one line, truncating if necessary.
     $*$  `n`, `N`: pretty format on one line without truncation.

See also:printf3 examplesSign in to add an example

# Print out the current time in Last-Modified header-compliant 
# form. (reference: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Last-Modified)
(def weekdayMap [ "Sun" "Mon" "Tue" "Wed" "Thu" "Fri" "Sat" ])
(def monthMap ["Jan" "Feb" "Mar" "Apr" "May" "Jun" "Jul" "Aug" "Sep" "Oct" "Nov" "Dec"])
(def dt (os/date (os/time) true))
(string/format "%s, %02d %s %04d %02d:%02d:%02d" 
     (weekdayMap (dt :week-day)) 
     (dt :month-day)
     (monthMap (dt :month))
     (dt :year)
     (dt :hours)
     (dt :minutes)
     (dt :seconds))

yumaikasPlayground

# There is a list of formatters here: https://janet-lang.org/capi/writing-c-functions.html


(string/format "With terminal colors: %M" [:array {:key-in "struct"}]) # => "With terminal colors: (\e[33m:array\e[0m {\e[33m:key-in\e[0m \e[35m\"struct\"\e[0m})"

roobiePlayground

You can see janet datastructure values by typing:

(string/format "%q" {:a 1 :b 2}) # => {:a 1 :b 2}

swlkrPlayground