Commonly used macro compilation definition: allows code to be executed under different compilation Conditions

(1) _ optimize _: used to determine release and Debug. When _ optimize _ is selected, the code can be executed during release, but not during debug. Example:

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#ifndef __OPTIMIZE__      // In debug modeelse    // In the release mode#endif

(2) _ i386 _ and _ x86_64 _: used to judge the simulator environment and the real machine environment. The code that meets this condition is only executed in the simulator. The sample code is as follows:

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#if defined (__i386__) || defined (__x86_64__)         // Run the command in the simulator.#else         // Execute on a real machine#endif

(3) _ iphone_ OS _version_max_allowed: The current compiled SDK version, which can be compared with macro definitions such as _ iphone_9_0 for code execution in different versions. Example:

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if (__IPHONE_OS_VERSION_MAX_ALLOWED == __IPHONE_9_0) {          // If the current SDK version is 9.0, execute the code here    }else{          // Otherwise, run the following command:    }

[16] pre-compiled macro # ifdef # else # endif

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#ifdef ****      // Code 1else    // Code 2#endif

This means that if the identifier *** has been defined by the # define command, code 1 is compiled; otherwise, code 2 is compiled.

There are also # ifndef, which is the opposite of # ifdef.

Commonly used macro compilation definition: allows code to be executed under different compilation Conditions