借用gcc内置函数帮助C来实现函数重载

借用gcc内置函数__builtin_choose_expr和__builtin_types_compatible_p可以帮助c来实现函数重载。

首先对这两个函数功能做下介绍

__builtin_choose_expr(expr,expr1,expr2)与c语言:?运算符有些类似，如果expr表达式为真，那么返回expr1,否则返回expr2

_builtin_types_compatible_p(type1,type2)测试type1与type2是否相同，如果相同返回真，否则返回假

#include <stdio.h>

struct s1
{
    int a;
    int b;
};

struct s2
{
    double a;
    double b;
};

void over_load_s1(struct s1 s)
{
    printf("This is over_load_s1\n");
}

void over_load_s2(struct s2 s)
{
    printf("This is over_load_s2\n");
}
/*下面的宏定义主要使用了__builtin_choose_expr里嵌套了另一个__built_in_choose_expr函数
如果类型为struct s1，则返回over_load_s1的调用结果，如果类型为struct s2,则返回over_loads2的调用结果，否则显示出错信息*/
#define over_load(A)\
    __builtin_choose_expr(__builtin_types_compatible_p(typeof(A), struct s1),\
             over_load_s1(*(struct s1 *)&A),\
    __builtin_choose_expr(__builtin_types_compatible_p(typeof(A), struct s2), \
              over_load_s2(*(struct s2 *)&A),\
    printf("don't support this type parameter,please check again\n")))

int main()
{
    struct s1 s1 = {1, 2};
    struct s2 s2 = {1.1, 2.2};
    over_load(s1);
    over_load(s2);
    over_load(2);
}