C语言宏定义的几种简单用法

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1、计算数组的大小

#define countof(a) (sizeof(a)/sizeof(*(a)))

2、转换大小写字母

#define FS_TOUPPER(x) ((((x) >= 'a') && ((x) <= 'z')) ? (x) - 'a' + 'A' : (x))#define FS_TOLOWER(x) ((((x) >= 'A') && ((x) <= 'Z')) ? (x) - 'A' + 'a' : (x))

3、大小端模式转换

#define SWAP16(x) (((x) << 8) & 0xff00) | (((x) >> 8) & 0xff)#define SWAP32(x) ((((uint32_t)(x) >> 24) & 0xff) | (((uint32_t)(x) >> 8) & 0xff00) | (((uint32_t)(x) << 8) & 0xff0000) | (((uint32_t)(x) << 24) & 0xff000000))

4、生成字，双字

#define MAKE_DWORD(b3, b2, b1, b0) (((uint32_t)((uint8_t)(b3) << 24)) | ((uint8_t)(b2) << 16) | ((uint8_t)(b1) << 8) | ((uint8_t)(b0)))#define MAKE_WORD(h, l)  (((uint32_t)(h) << 8) | ((l) & 0xffff))

5、获取高，低字节

#define GET_WORD_HIGH(x) ((uint32_t)(x) >> 16)#define GET_WORD_LOW(x)  ((uint32_t)(x) & 0xffff)#define GET_WORD_HIGHBYTE(x) ((uint32_t)(x) >> 24)#define GET_WORD_LOWBYTE(x)   ((uint32_t)(x) & 0xff)

以上宏定义的示例程序

#include <stdio.h>#include <stdint.h>#define countof(a) (sizeof(a)/sizeof(*(a)))#define FS_TOUPPER(x) ((((x) >= 'a') && ((x) <= 'z')) ? (x) - 'a' + 'A' : (x))#define FS_TOLOWER(x) ((((x) >= 'A') && ((x) <= 'Z')) ? (x) - 'A' + 'a' : (x))#define SWAP16(x) (((x) << 8) & 0xff00) | (((x) >> 8) & 0xff)#define SWAP32(x) ((((uint32_t)(x) >> 24) & 0xff) | (((uint32_t)(x) >> 8) & 0xff00) | (((uint32_t)(x) << 8) & 0xff0000) | (((uint32_t)(x) << 24) & 0xff000000))#define MAKE_DWORD(b3, b2, b1, b0) (((uint32_t)((uint8_t)(b3) << 24)) | ((uint8_t)(b2) << 16) | ((uint8_t)(b1) << 8) | ((uint8_t)(b0)))#define MAKE_WORD(h, l)  (((uint32_t)(h) << 8) | ((l) & 0xffff))#define GET_WORD_HIGH(x) ((uint32_t)(x) >> 16)#define GET_WORD_LOW(x)  ((uint32_t)(x) & 0xffff)#define GET_WORD_HIGHBYTE(x) ((uint32_t)(x) >> 24)#define GET_WORD_LOWBYTE(x) ((uint32_t)(x) & 0xff)void test_countof(){    int a[10] = {};    printf("%d\n",countof(a));}void test_FSTOUPPER(){    char a[14] = "This is a test";    char ans_up[14];    char ans_low[14];    for (int i = 0;i<14;i++){        ans_up[i] = FS_TOUPPER(a[i]);        printf("%c",ans_up[i]);    }    printf("\n");    for (int j = 0; j<14; j++){        ans_low[j] = FS_TOLOWER(ans_up[j]);        printf("%c",ans_low[j]);    }}void test_SWAP(){    uint16_t x = 0x1234;    uint32_t y = 0x12345678;    printf("%x\n",SWAP16(x));    printf("%x\n",SWAP32(y));}void test_MAKE_WORD(){    uint8_t a = 0x12;    uint8_t b = 0x34;    uint8_t c = 0x56;    uint8_t d = 0x78;    printf("%x\n",MAKE_WORD(a,b));    printf("%x\n",MAKE_DWORD(a,b,c,d));}void test_GET_WORD(){    uint32_t a = 0x12345678;    printf("%x\n",GET_WORD_HIGH(a));    printf("%x\n",GET_WORD_LOW(a));    printf("%x\n",GET_WORD_HIGHBYTE(a));    printf("%x\n",GET_WORD_LOWBYTE(a));}void main(void) {    test_countof();    test_FSTOUPPER();    test_SWAP();    test_MAKE_WORD();    test_GET_WORD();}

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