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IMHO, все четко и ясно....
The `#if' directive allows you to test the value of an arithmetic expression, rather than the mere existence of one macro. Its syntax is
#if expression
controlled text
#endif /* expression */
expression is a C expression of integer type, subject to stringent restrictions. It may contain
- Integer constants.
- Character constants, which are interpreted as they would be in normal code.
- Arithmetic operators for addition, subtraction, multiplication, division, bitwise operations, shifts, comparisons, and logical operations (&& and ||). The latter two obey the usual short-circuiting rules of standard C.
- Macros. All macros in the expression are expanded before actual computation of the expression's value begins.
- Uses of the defined operator, which lets you check whether macros are defined in the middle of an `#if'.
- Identifiers that are not macros, which are all considered to be the number zero. This allows you to write #if MACRO instead of #ifdef MACRO, if you know that MACRO, when defined, will always have a nonzero value. Function-like macros used without their function call parentheses are also treated as zero.
Так что, увы, никакого float там.
Однако, никто не мешает на оптимизатор возложить часть расчетов. Всякие там if (0) {} им убиваются на раз, и типы он преобразует как надо.
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Да неужто нет никакого способа С-препроцессором проверить float на больше-меньше?
Dec 6 2014, 11:33
