3 Examples top

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  ;; See http://download.oracle.com/javase/1.5.0/docs/api/java/util/Formatter.html
  ;; for formatting options.
  user=> (format "Hello there, %s" "bob")
  "Hello there, bob"
  

  ;; See http://download.oracle.com/javase/1.5.0/docs/api/java/util/Formatter.html ;; for formatting options. user=> (format "Hello there, %s" "bob") "Hello there, bob"
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  user=> (format "%5d" 3)
  "    3"
  
  user=> (format "Pad with leading zeros %07d" 5432)
  "Pad with leading zeros 0005432"
  
  user=> (format "Left justified :%-7d:" 5432)
  "Left justified :5432   :"
  
  user=> (format "Locale-specific group separators %,12d" 1234567)
  "Locale-specific group separators    1,234,567"
  
  user=> (format "decimal %d  octal %o  hex %x  upper-case hex %X" 63 63 63 63)
  "decimal 63  octal 77  hex 3f  upper-case hex 3F"
  
  ;;    ====== Clojure format/printf and large integers =====
  
  ;; This big number doesn't fit in a Long.  It is a
  ;; clojure.lang.BigInt, which format cannot handle directly.
  user=> (format "%5d" 12345678901234567890)
  IllegalFormatConversionException d != clojure.lang.BigInt  java.util.Formatter$FormatSpecifier.failConversion (Formatter.java:3999)
  
  ;; You can convert it to a java.math.BigInteger, which format does handle.
  user=> (format "%5d" (biginteger 12345678901234567890))
  "12345678901234567890"
  
  ;; If you do this very often, you might want to use something like
  ;; format-plus to avoid sprinkling your code with calls to biginteger.
  (defn coerce-unformattable-types [args]
    (map (fn [x]
           (cond (instance? clojure.lang.BigInt x) (biginteger x)
                 (instance? clojure.lang.Ratio x) (double x)
                 :else x))
         args))
  
  (defn format-plus [fmt & args]
    (apply format fmt (coerce-unformattable-types args)))
  
  ;; Now this works:
  user=> (format-plus "%5d" 12345678901234567890)
  "12345678901234567890"

  user=> (format "%5d" 3) " 3" user=> (format "Pad with leading zeros %07d" 5432) "Pad with leading zeros 0005432" user=> (format "Left justified :%-7d:" 5432) "Left justified :5432 :" user=> (format "Locale-specific group separators %,12d" 1234567) "Locale-specific group separators 1,234,567" user=> (format "decimal %d octal %o hex %x upper-case hex %X" 63 63 63 63) "decimal 63 octal 77 hex 3f upper-case hex 3F" ;; ====== Clojure format/printf and large integers ===== ;; This big number doesn't fit in a Long. It is a ;; clojure.lang.BigInt, which format cannot handle directly. user=> (format "%5d" 12345678901234567890) IllegalFormatConversionException d != clojure.lang.BigInt java.util.Formatter$FormatSpecifier.failConversion (Formatter.java:3999) ;; You can convert it to a java.math.BigInteger, which format does handle. user=> (format "%5d" (biginteger 12345678901234567890)) "12345678901234567890" ;; If you do this very often, you might want to use something like ;; format-plus to avoid sprinkling your code with calls to biginteger. (defn coerce-unformattable-types [args] (map (fn [x] (cond (instance? clojure.lang.BigInt x) (biginteger x) (instance? clojure.lang.Ratio x) (double x) :else x)) args)) (defn format-plus [fmt & args] (apply format fmt (coerce-unformattable-types args))) ;; Now this works: user=> (format-plus "%5d" 12345678901234567890) "12345678901234567890"
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  ;;  ==== Clojure format/printf and floating-point formats ====
  user=> (format "%.3f" 2.0)
  "2.000"
  
  ;; format doesn't handle integers or ratios with %e, %f, %g, or %a
  user=> (format "%.3f" 2)
  IllegalFormatConversionException f != java.lang.Long  java.util.Formatter$FormatSpecifier.failConversion (Formatter.java:3999)
  
  ;; In general, if you want to use floating-point formats %e, %f, %g,
  ;; or %a with format or printf, and you don't know whether the values
  ;; you want to format are floats or doubles, you should convert them:
  user=> (format "%.3f" (double 2))
  "2.000"
  
  user=> (format "%.3f" (double (/ 5 2)))
  "2.500"
  
  ;; One could make a function that parses the format string to look for
  ;; %f and other floating-point formats and automatically coerces the
  ;; corresponding arguments to doubles, but such a function probably
  ;; wouldn't fit into a short example.  You could also consider using
  ;; cl-format which does handle these kinds of things for you.  The main
  ;; disadvantage to doing so is that you have to learn a different syntax
  ;; for format specifiers.

  ;; ==== Clojure format/printf and floating-point formats ==== user=> (format "%.3f" 2.0) "2.000" ;; format doesn't handle integers or ratios with %e, %f, %g, or %a user=> (format "%.3f" 2) IllegalFormatConversionException f != java.lang.Long java.util.Formatter$FormatSpecifier.failConversion (Formatter.java:3999) ;; In general, if you want to use floating-point formats %e, %f, %g, ;; or %a with format or printf, and you don't know whether the values ;; you want to format are floats or doubles, you should convert them: user=> (format "%.3f" (double 2)) "2.000" user=> (format "%.3f" (double (/ 5 2))) "2.500" ;; One could make a function that parses the format string to look for ;; %f and other floating-point formats and automatically coerces the ;; corresponding arguments to doubles, but such a function probably ;; wouldn't fit into a short example. You could also consider using ;; cl-format which does handle these kinds of things for you. The main ;; disadvantage to doing so is that you have to learn a different syntax ;; for format specifiers.