C语言宏定义的几种简单用法

• 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();
}