iOS Development Summary (A0)-#define and const

When to use # define, when to use const?

Effective Objective C ITEM4 says this:

Prefer Typed Constants to preprocessor #define

1. Avoid # define. Because there is no type information, and may be redefined

2. defined as a static const in M files (in fact this process is the same as # define)

3. For global constants, it should be stated in the header file, defined in the relevant m file, that the class name prefixed with the response

As in. h,

extern const Nstimerinterval Classanimationduration;

In. M,

Const Nstimerinterval? classanimationduration=0.3;

(As with various Notificaiton in uiapplication)

?

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Note the const position, which modifies the const key before the keyword, such as

Static NSString * Const CONSTANT; Refers to the const pointer to an NSString

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iOS Development Summary (A0)-#define and const