C Language and Libraries Help (clang.hlp) (Table of Contents; Topic list)
printf Type Characters: Floating-Point
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─────Run-Time Library───────────────────────────────────────────────────────
 
     All of the type characters in this group are for arguments of type
     double.
 
     Character     Output Format
 
     f             12.345 or -12.345
 
     e             1.234e123 or 1.2345e-012 (etc.)
 
     E             Identical to e format, except with E instead of e
 
     g             Signed value in f or e format, whichever is more
                   compact
 
     G             Identical to the g format, except that E introduces
                   the exponent
 
     If the argument is infinite, indefinite, or not-a-number (NAN),
     printf gives the following output:
 
     Value            Output
 
     + infinity       1.#INFrandom-digits
     - infinity       -1.#INFrandom-digits
     Indefinite       digit.#INDrandom-digits
     Not-a-number     digit.#NANrandom-digits
                                    -♦-