If the value of dDate
is -0x1.fffffffffffffp1023
, then the %f
format specifier produces “-179769313486231570814527423731704356798070567525844996598917476803157260780028538760589558632766878171540458953514382464234321326889464182768467546703537516986049910576551282076245490090389328944075868508455133942304583236903222948165808559332123348274797826204144723168738177180919299881250404026184124858368.000000”, which contains 317 characters. Adding the ten other characters in the format string and the null terminator results in 328 characters.
-0x1.fffffffffffffp1023
is the greatest magnitude finite negative number representable in IEEE-754 64-bit binary floating-point. Although it is not represented with the precision suggested by the formatted decimal number, it does represent exactly that number.
(The C standard may allow a somewhat different display, such as showing zeros beyond a certain point instead of the exact digits. However, the number of digits displayed should be the same. A good C implementation will show all the exact digits.)