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<!--There is also a #ifndef command which has the opposite effect. The code that follows is only compiled if the macro is not defined.-->

<!--There is also a #ifndef command which has the opposite effect. The code that follows is only compiled if the macro is not defined.-->

Например макрос DEBUG можно включать для определённого участка кода:

Например макрос DEBUG можно включать для определённого участка кода при помощи #ifdef :

<!--The DEBUG macro is sometimes used to turn on certain debugging features in the code. The following example demonstrates this technique.-->

<!--The DEBUG macro is sometimes used to turn on certain debugging features in the code. The following example demonstrates this technique.-->

====#if====

====#if====

The #if command is a more general version of the #ifdef command because it can take any expression involving other macros and constants. If the expression is true, the code which follows is compiled. Otherwise it is skipped. Alternate conditions can be supplied with the #elif command and a final section to be compiled if all else fails may follow the #else command.

Команда #if - более общая версия #ifdef, так как включает определения не только макросов но и констант. То есть если выражение совпадает (true), то код внутри #if будет скомпилирован, если выражение не совпадает (false), то код не будет выполняться. В случае невыполнения условий применяется команда #elif, а в случае невыполнения никаких условий из заданных вами, используется команда #else.

<!--command is a more general version of the #ifdef command because it can take any expression involving other macros and constants. If the expression is true, the code which follows is compiled. Otherwise it is skipped. Alternate conditions can be supplied with the #elif command and a final section to be compiled if all else fails may follow the #else command.-->

: #if Condition

: #if Условие

//Conditional code.

//Код условия.

: #elif Condition

: #elif Условие

//Conditional code.

//Код условия.

: #else

: #else

//Conditional code.

//Код условия.

: #endif

: #endif

The condition may involve any of the basic operators but usually only uses the boolean operators. One addition is the defined instruction which tests if the specified macro has been defined.

<!--The condition may involve any of the basic operators but usually only uses the boolean operators. One addition is the defined instruction which tests if the specified macro has been defined.-->

defined (Macro)

defined (Macro)

Macro is the name of a macro.

Macro - название макроса.

Returns 1 if macro has been defined and 0 if not.

Выдаёт 1 (Returns 1) если макрос определён <!--if macro has been defined--> и 0, если не был.

One common use of the #if command is to block out a section of code. This is sometimes done in the course of debugging or possibly to turn off a feature without throwing away the code. The following example demonstrates this technique.

Часто команда #if используется для блокировки выполнения куска кода - в случае если происходит краш, или нужно выключить какую-либо фичу без выпиливания куска кода. Вот пример выполнения кода:

<!--One common use of the #if command is to block out a section of code. This is sometimes done in the course of debugging or possibly to turn off a feature without throwing away the code. The following example demonstrates this technique.-->

: #if 0

: #if 0