在初学C语言，接触指针的时候，真的是比较迷惑的一件事，恰巧指针还和自增运算符碰到一起了，更是碰出了无限的可能，正所谓两仪生四象，四象生八卦啊
为了期末考试，彻底弄明白指针和自增运算符在一起时的各种可能和现象，我们可以直接通过编写C代码来试验一下
先上结论：
(*p)++,先传值,后值自增1,类比a++
*p++ == *(p++),先传值,后地址自增1
++*p == ++(*p),先值自增1,后传值,类比++a
*++p == *(++p),先地址自增1,后传值
代码中设计了ABCDEFG一共7种可能会出现的情况，对应着ABCDEFG这7个函数
| 函数名 | 类型 |
|---|---|
| A | (*p)++ |
| B | *p++ |
| C | *(p++) |
| D | ++*p |
| E | ++(*p) |
| F | *++p |
| G | *(++p) |
然后通过传入一个数组[10,20,30]，让指针和自增在数组上进行造作，看看最后是什么结果，指针的值有什么变化，来推断出7种可能的结论
源码可以运行，方便更直观的看出指针与自增在一起的运算顺序
#include <stdio.h>
void A(int array[3])
{
int *p = NULL;//定义一个指针
p = array;//指向数组的首地址，以方便观察指针的移动情况，后续的函数B~G类似
printf("----- A -----
");
printf("> *p=%d
",*p);
printf("printf("> (*p)++=%%d\n",(*p)++);
");
printf("> (*p)++=%d
",(*p)++);//> (*p)++=10,先传值,后值自增1,类比a++
printf("
");
printf("printf("> *p=%%d\n",*p);
");
printf("> *p=%d
",*p);//> *p=11
printf("
");
}
void B(int array[3])
{
int *p = NULL;
p = array;
printf("----- B -----
");
printf("> *p=%d
",*p);
printf("printf("> *p++=%%d\n",*p++);
");
printf("> *p++=%d
",*p++);//> *p++=10,先传值,后地址自增1
printf("
");
printf("*printf("> *p=%%d\n",*p);
");
printf("> *p=%d
",*p);//> *p=20
printf("
");
}
void C(int array[3])
{
int *p = NULL;
p = array;
printf("----- C -----
");
printf("> *p=%d
",*p);
printf("printf("> *(p++)=%%d\n",*(p++));
");
printf("> *(p++)=%d
",*(p++));//> *(p++)=10,先传值,后地址自增1
printf("
");
printf("printf("> *p=%%d\n",*p);
");
printf("> *p=%d
",*p);//> *p=20
printf("
");
}
void D(int array[3])
{
int *p = NULL;
p = array;
printf("----- D -----
");
printf("> *p=%d
",*p);
printf("printf("> ++*p=%%d\n",++*p);
");
printf("> ++*p=%d
",++*p);//> ++*p=11,先值自增1,后传值
printf("
");
printf("printf("> *p=%%d\n",*p);
");
printf("> *p=%d
",*p);//> *p=11
printf("
");
}
void E(int array[3])
{
int *p = NULL;
p = array;
printf("----- E -----
");
printf("> *p=%d
",*p);
printf("printf("> ++(*p)=%%d\n",++(*p));
");
printf("> ++(*p)=%d
",++(*p));//> ++(*p)=11,先值自增1,后传值,类比++a
printf("
");
printf("printf("> *p=%%d\n",*p);
");
printf("> *p=%d
",*p);//> *p=11
printf("
");
}
void F(int array[3])
{
int *p = NULL;
p = array;
printf("----- F -----
");
printf("> *p=%d
",*p);
printf("printf("> *++p=%%d\n",*++p);
");
printf("> *++p=%d
",*++p);//> *++p=20,先地址自增1,后传值
printf("
");
printf("printf("> *p=%%d\n",*p);
");
printf("> *p=%d
",*p);//> *p=20
printf("
");
}
void G(int array[3])
{
int *p = NULL;
p = array;
printf("----- G -----
");
printf("> *p=%d
",*p);
printf("printf("> *(++p)=%%d\n",*(++p));
");
printf("> *(++p)=%d
",*(++p));//> *(++p)=20,先地址自增1,后传值
printf("
");
printf("printf("> *p=%%d\n",*p);
");
printf("> *p=%d
",*p);//> *p=20
printf("
");
}
int main(void)
{
int a[3]={10,20,30},b[3]={10,20,30},c[3]={10,20,30},d[3]={10,20,30},e[3]={10,20,30},f[3]={10,20,30},g[3]={10,20,30};
printf("array[3]={10,20,30}
p=array
");
A(a); // (*p)++ 先传值,后值自增1,类比a++
B(b); // *p++ == *(p++) 先传值,后地址自增1
C(c); // *(p++) == *p++ 先传值,后地址自增1
D(d); // ++*p == ++(*p) 先值自增1,后传值
E(e); // ++(*p) == ++*p 先值自增1,后传值,类比++a
F(f); // *++p == *(++p) 先地址自增1,后传值
G(g); // *(++p) == *++p 先地址自增1,后传值
printf("
>> A ---> (*p)++,先传值,后值自增1,类比a++
>> B==C ---> *p++ == *(p++),先传值,后地址自增1
>> D==E ---> ++*p == ++(*p),先值自增1,后传值,类比++a
>> F==G ---> *++p == *(++p),先地址自增1,后传值
");
return 0;
}
执行结果
array[3]={10,20,30}
p=array
----- A -----
> *p=10
printf("> (*p)++=%d
",(*p)++);
> (*p)++=10
printf("> *p=%d
",*p);
> *p=11
----- B -----
> *p=10
printf("> *p++=%d
",*p++);
> *p++=10
*printf("> *p=%d
",*p);
> *p=20
----- C -----
> *p=10
printf("> *(p++)=%d
",*(p++));
> *(p++)=10
printf("> *p=%d
",*p);
> *p=20
----- D -----
> *p=10
printf("> ++*p=%d
",++*p);
> ++*p=11
printf("> *p=%d
",*p);
> *p=11
----- E -----
> *p=10
printf("> ++(*p)=%d
",++(*p));
> ++(*p)=11
printf("> *p=%d
",*p);
> *p=11
----- F -----
> *p=10
printf("> *++p=%d
",*++p);
> *++p=20
printf("> *p=%d
",*p);
> *p=20
----- G -----
> *p=10
printf("> *(++p)=%d
",*(++p));
> *(++p)=20
printf("> *p=%d
",*p);
> *p=20
>> A ---> (*p)++,先传值,后值自增1,类比a++
>> B==C ---> *p++ == *(p++),先传值,后地址自增1
>> D==E ---> ++*p == ++(*p),先值自增1,后传值,类比++a
>> F==G ---> *++p == *(++p),先地址自增1,后传值