Type Encodings

编码表

Objective-C type encodings

Code	Meaning
c	A char
i	An int
s	A short
l	A long l is treated as a 32-bit quantity on 64-bit programs.
q	A long long
C	An unsigned char
I	An unsigned int
S	An unsigned short
L	An unsigned long
Q	An unsigned long long
f	A float
d	A double
B	A C++ bool or a C99 _Bool
v	A void
*	A character string (char *)
@	An object (whether statically typed or typed id)
#	A class object (Class)
:	A method selector (SEL)
[array type]	An array
{name=type... }	A structure
(name=type... )	A union
bnum	A bit field of num bits
^type	A pointer to type
?	An unknown type (among other things, this code is used for function pointers)

或者通过下面方法打印查看：

void lgTypes(){
    NSLog(@"char --> %s",@encode(char));
    NSLog(@"int --> %s",@encode(int));
    NSLog(@"short --> %s",@encode(short));
    NSLog(@"long --> %s",@encode(long));
    NSLog(@"long long --> %s",@encode(long long));
    NSLog(@"unsigned char --> %s",@encode(unsigned char));
    NSLog(@"unsigned int --> %s",@encode(unsigned int));
    NSLog(@"unsigned short --> %s",@encode(unsigned short));
    NSLog(@"unsigned long --> %s",@encode(unsigned long long));
    NSLog(@"float --> %s",@encode(float));
    NSLog(@"bool --> %s",@encode(bool));
    NSLog(@"void --> %s",@encode(void));
    NSLog(@"char * --> %s",@encode(char *));
    NSLog(@"id --> %s",@encode(id));
    NSLog(@"Class --> %s",@encode(Class));
    NSLog(@"SEL --> %s",@encode(SEL));
    int array[] = {1,2,3};
    NSLog(@"int[] --> %s",@encode(typeof(array)));
    typedef struct person{
        char *name;
        int age;
    }Person;
    NSLog(@"struct --> %s",@encode(Person));
    
    typedef union union_type{
        char *name;
        int a;
    }Union;
    NSLog(@"union --> %s",@encode(Union));

    int a = 2;
    int *b = {&a};
    NSLog(@"int[] --> %s",@encode(typeof(b)));
}

举例说明

通过clang -rewrite-objc main.m -o main.cpp
查看main.cpp文件
会有sel和imp及编码表。
sel：方法编号 就像书的目录
imp：函数指针地址 就像书的页码

上图的@、v等类型标识编码，在xcode中 command + shift + o查找调用ivar_getTypeEncoding方法也可以获取对应的编码。 以上图nickName为例，get方法:

• nickName"，@16@0:8" ：
  • @表示id类型返回值
  • 16:开辟16字节内存
  • @表示id类型，第一个参数方法默认带的参数self
  • 0表示从0开始 前一个@标识id 所以0-8字节
  • ：表示sel 从第8字节开始，占8字节