C语言14 指针类型
指针是C语言中的一种数据类型，
定义带 "*"类型的变量
char x; char* x;
short y; short* y;
int z; int* z;
float f; float* f;
double d; double* d;
Student st; Student* st;
总结:
- 任何带有
*的变量类型的标准写法：变量类型* 变量名 - 任何类型都可以带
*加上*以后是新的类型，统称为“指针类型” -
*可以使任意多个。
指针变量赋值
char* x; char*** x; char******* x;
short* ~~
int* ~~
Student* ~~
x = (char*)1;
y = (short*)2;
~~~
int******* x;
int******* y;
x = (int*******)4;
y = x;
char x;
x = 1;
指针变量的宽度
char x; char* x; char******** x;
short y; short* y; short******** y;
~~
x=1; x=(char*)1; x=(char********)1;
~~
9: char* x;
10: short* y;
11: int* z;
12:
13: x = (char*)1;
00401028 C7 45 FC 01 00 00 00 mov dword ptr [ebp-4],1
14: y=(short*)2;
0040102F C7 45 F8 02 00 00 00 mov dword ptr [ebp-8],2
15: z=(int*)3;
00401036 C7 45 F4 03 00 00 00 mov dword ptr [ebp-0Ch],3
9: char******** x;
10: short******** y;
11: int******** z;
12:
13: x = (char********)1;
00401028 C7 45 FC 01 00 00 00 mov dword ptr [ebp-4],1
14: y=(short********)2;
0040102F C7 45 F8 02 00 00 00 mov dword ptr [ebp-8],2
15: z=(int********)3;
00401036 C7 45 F4 03 00 00 00 mov dword ptr [ebp-0Ch],3
总结：
指针类型的变量宽度永远是4字节、无论类型是什么 无论有几个*。
指针类型自加和自减(++ / --)
char a; char**** a;
short b; short**** b;
int c; int**** c;
a=100; a=(char****)100;
b=100; b=(short****)100;
c=100; c=(int****)100;
a++; a++;
b++; b++;
c++; c++;
printf("%d %d %d",a,b,c); printf("%d %d %d",a,b,c);
11: char* a;
12: short* b;
13: int* c;
14: a=(char*)100;
0040B488 C7 45 FC 64 00 00 00 mov dword ptr [ebp-4],64h
15: b=(short*)100;
0040B48F C7 45 F8 64 00 00 00 mov dword ptr [ebp-8],64h
16: c=(int*)100;
0040B496 C7 45 F4 64 00 00 00 mov dword ptr [ebp-0Ch],64h
17: a++;
0040B49D 8B 45 FC mov eax,dword ptr [ebp-4]
0040B4A0 83 C0 01 add eax,1
0040B4A3 89 45 FC mov dword ptr [ebp-4],eax
18: b++;
0040B4A6 8B 4D F8 mov ecx,dword ptr [ebp-8]
0040B4A9 83 C1 02 add ecx,2
0040B4AC 89 4D F8 mov dword ptr [ebp-8],ecx
19: c++;
0040B4AF 8B 55 F4 mov edx,dword ptr [ebp-0Ch]
0040B4B2 83 C2 04 add edx,4
0040B4B5 89 55 F4 mov dword ptr [ebp-0Ch],edx
比如
int* c =1; c++; 去掉* 是int 4个字节 就+4;
char* c=1; c++; 去掉* 是char 1个字节 就+1
char** c=1; c++; 去掉* 是char* 指针类型是4个字节 就+4
指针类型变量+N=指针类型变量+N*(去掉一个*后类型的宽度)
指针类型变量-N=指针类型变量-N*(去掉一个*后类型的宽度)
总结、
- 不带
*变量的变量，++或者--都是加1 或者减1 - 带
*类型的变量m,++或者-- 新增（减少）的数量是去掉一个*后变量的宽度
image
指针类型的比较
char**** a;
char**** b;
a = (char****)200;
b = (char****)100;
if(a>b)
{
printf("1");
}
else
{
printf("2");
}
12: char**** a;
13: char**** b;
14: a = (char****)200;
0040B488 C7 45 FC C8 00 00 00 mov dword ptr [ebp-4],0C8h
15: b = (char****)100;
0040B48F C7 45 F8 64 00 00 00 mov dword ptr [ebp-8],64h
16: if(a>b)
0040B496 8B 45 FC mov eax,dword ptr [ebp-4]
0040B499 3B 45 F8 cmp eax,dword ptr [ebp-8]
0040B49C 76 0F jbe main+3Dh (0040b4ad)
17: {
18: printf("1");
0040B49E 68 1C F0 41 00 push offset string "1" (0041f01c)
0040B4A3 E8 A8 02 00 00 call printf (0040b750)
0040B4A8 83 C4 04 add esp,4
19: }
20: else
0040B4AB EB 0D jmp main+4Ah (0040b4ba)
21: {
22: printf("2");
0040B4AD 68 50 FE 41 00 push offset string "2" (0041fe50)
0040B4B2 E8 99 02 00 00 call printf (0040b750)
0040B4B7 83 C4 04 add esp,4
//这里编译器使用了jbe指令 jbe指令是用来比较无符号数的，也就说明指针类型是无符号数
总结
指针类型可以做大小比较
image
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