循环展开指定的代码段N次

由于宏在展开期间只是简单的字符串替换，不能执行数值计算，因此需要通过递归的方式进行展开。因此当展开层数较多时，需要较多的样板代码。

#include <stdio.h>

#define DECLARE_VARIABLE(n) \
    ret = of_property_read_u32(np, "sme,lter" # n, &val); \
    if (val == 0 || ret < 0) \
        return -EINVAL; \
    tc->lter##n = val;

#define EXPAND_VARIABLES_0()
#define EXPAND_VARIABLES_1() DECLARE_VARIABLE(1)
#define EXPAND_VARIABLES_2() DECLARE_VARIABLE(2) EXPAND_VARIABLES_1()
#define EXPAND_VARIABLES_3() DECLARE_VARIABLE(3) EXPAND_VARIABLES_2()
#define EXPAND_VARIABLES_4() DECLARE_VARIABLE(4) EXPAND_VARIABLES_3()

#define EXPAND_VARIABLES(count) EXPAND_VARIABLES_HELPER(count)
#define EXPAND_VARIABLES_HELPER(count) \
    EXPAND_VARIABLES_##count()
// Add more EXPAND_VARIABLES_n() definitions as needed

int main() {
    EXPAND_VARIABLES(3)
    printf("Variables declared successfully.\n");
    return 0;
}