2014年03月30日

iOS(const) const的基本用法

 

基本用法: 修饰变量, 使其值不可更改:

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const int a = 1;

a = 2;//ERROR: Read-only variable is not assignable

const配合指针时:

情况一, const放在*前面, 则指针指向的值不能改变,

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int a = 1;

const int *pa = &a;

*pa = 2; // ERROR: Read-only variable is not assignable

情况二, const放到*后面,则指针不能指向别处,

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int a = 1, b = 2;

int * const pa = &a;

pa = &b; // ERROR: Read-only variable is not assignable

情况三, *左右皆放置const,则指针既不可改其值, 又不可指向别处

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int a = 1, b = 2;

const int * const pa = &a;

pa = &b; // ERROR: Read-only variable is not assignable

*pa = 3; // ERROR: Read-only variable is not assignable




综合以上问题，可以解决iOS关于变量于常量之间

Capturing 'self' strongly in this block is likely to lead to aretain cycle

的警告。