前提：在XCode做開發調試時往往需要打印一些調試信息做debug用，大家知道當打印信息的地方多了之後在模擬器上跑可能不會有什麼問題，因爲模擬器用的是電腦的硬件但是當應用跑在設備上時這些輸出語句會在很大程度上影響應用的性能，針對這種問題可以寫一些宏來控制這些調試信息的輸出。
在release版本禁止輸出NSLog內容
因爲NSLog的輸出還是比較消耗系統資源的，而且輸出的數據也可能會暴露出App裏的保密數據，所以發佈正式版時需要把這些輸出全部屏蔽掉。
我們可以在發佈版本前先把所有NSLog語句註釋掉，等以後要調試時，再取消這些註釋，這實在是一件無趣而耗時的事！還好，還有更優雅的解決方法，就是在項目的prefix.pch文件里加入下面一段代碼，加入後，NSLog就只在Debug下有輸出，Release下不輸出了。
如何實現：
- #ifdef DEBUG
- #define NSLog(fmt,...) do{NSLog(fmt,##__VA_ARGS__);} while(0)
- #define debugMethod() NSLog(@"%s", __func__)
- #else
- #define NSLog(...) do{}while(0)
- #define debugMethod()
- #endif
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//DLog will output like NSLog only when the DEBUG variable is set #ifdef DEBUG #define DLog(fmt, ...) do{ NSLog((@"%s [Line %d] " fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__);}while(0) #else #define DLog(...) do{}while(0) #endif // ALog will always output like NSLog #define ALog(fmt, ...) do{NSLog((@"%s [Line %d] " fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__);}while(0) // ULog will show the UIAlertView only when the DEBUG variable is set #ifdef DEBUG #define ULog(fmt, ...) do{ UIAlertView *alert = [[UIAlertView alloc] initWithTitle:[NSString stringWithFormat:@"%s\n [Line %d] ", __PRETTY_FUNCTION__, __LINE__] message:[NSString stringWithFormat:fmt, ##__VA_ARGS__] delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil]; [alert show]; }while(0) #else #define ULog(...) do{}while(0) #endif
|
上段代碼的意思就是 用宏指令做一個判斷，如果DEBUG爲真，則編譯#ifdef到#endif宏定義，否則編譯器就不編譯；
這個DEBUG在哪設置呢，
在 "Target > Build Settings > Preprocessor Macros > Debug" 裏有一個"DEBUG=1"。
設置爲Debug模式下，Product-->Scheme-->SchemeEdit Scheme#ifdef DEBUG
#define NSLog(format, ...) do{ \
fprintf(stderr,"<%s : %d> %s\n", \
[[[NSString stringWithUTF8String:__FILE__] lastPathComponent] UTF8String], \
__LINE__, __func__); \
(NSLog)((format), ##__VA_ARGS__); \
fprintf(stderr,"-------\n"); \
} while (0)
#else
#define NSLog(format, ...) do{}while(0)//release模式下,忽略
#endif
