C語言 - 使用Macro中##字號用法

1. ##: 將前後兩個的單詞拼接在一起

#define show_port(portname) show_##portname

調用show_port(mac0)展開後成為show_mac0

2. 程式範例

#include <stdio.h>

#define show_port(portname, port) \
static void show_##portname() \
{ \
        int val = 0; \
        val |= port; \
        printf("port = %s, ", #portname); \
        printf("val = 0x%04x\n", val); \
}

show_port(mac0, 0);
show_port(mac1, 1);
show_port(cpu, 2);

int main(int argc, char *argv[])
{
        show_mac0();
        show_mac1();
        show_cpu();
 
        return 0;
}

執行結果:
port = mac0, val = 0x0000
port = mac1, val = 0x0001
port = cpu, val = 0x0002

3. Macro展開後

show_port(mac0, 0);展開後
static void show_mac0()
{
    int val = 0;
    val |= 0;

    printf("port = %s, ", "mac0");
    printf("val = 0x%04x\n", val);
}
}

show_port(mac1, 1);展開後
static void show_mac1()
{
    int val = 0;
    val |= 1;

    printf("port = %s, ", "mac0");
    printf("val = 0x%04x\n", val);
}
}

show_port(cpu, 2);展開後
static void show_cpu()
{
    int val = 0;
    val |= 2;

    printf("port = %s, ", "cpu");
    printf("val = 0x%04x\n", val);
}