源码

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#include <stdio.h> 
 
typedef void (*pFunction)(void); //无返回值
typedef unsigned long (*pFunction2)(void); //有返回值 
 
unsigned long aaa(void) 
{ 
    printf("my address is %lx\r\n", (unsigned long)aaa); 
    return (unsigned long)aaa; //返回函数地址
} 
 
 
int main() 
{ 
    void (*p1)(void); 
 
    printf("void * - %ld\r\n",sizeof(void*))
    printf("unsigned int - %ld\r\n",sizeof(unsigned int));
    printf("unsigned long - %ld\r\n",sizeof(unsigned long));

    unsigned long b = 0;

    unsigned long a = aaa();
    printf("a = %lx\r\n",a);

    p1 = (void(*)(void))aaa; //显式转换
    p1();

    p1 = aaa; //隐式转换
    //b = p1();  //wrong

    p1 = a;	//直接使用地址
    p1();

    unsigned long (*p2)(void);	//定义函数指针
    p2 = a;	//直接使用地址
    b = p2();
    printf("b=%lx\r\n",b);

    ((void(*)())a)();
    b = ((unsigned long(*)())a)();
    printf("b=%lx\r\n",b);

    pFunction pp = aaa;
    pp();
    //b =  pp();  //wrong
    pp = a;
    pp();

    pFunction2 pp2 = a;
    b = pp2();
    printf("b=%lx\r\n",b);

    printf("a=%lx\r\n",a);
    pFunction f = (pFunction)a;
    f();

    pFunction f2 = (void(*)())a;
    f2();
    return 0;
}

结果

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ly@xxxx:test$ ./d
void * - 8
unsigned int - 4
unsigned long - 8
my address is 55d37b981149
a = 55d37b981149
my address is 55d37b981149
my address is 55d37b981149
my address is 55d37b981149
b=55d37b981149
my address is 55d37b981149
my address is 55d37b981149
b=55d37b981149
my address is 55d37b981149
my address is 55d37b981149
my address is 55d37b981149
b=55d37b981149
a=55d37b981149
my address is 55d37b981149
my address is 55d37b981149