頗龜毛: [C]實用巨集範例

除錯:

將描述式給一起印出

case1:

#define DPRINTF(expr) printf("%s=%d\n",#expr, expr)

#define DPRINTF(expr) printf(#expr"=%d",expr)

case2:

#define WARN_IF(EXP) \
     do { if (EXP) \
             fprintf (stderr, "Warning: " #EXP "\n"); } \
     while (0)

Note:

case1:

DPRINTF(x); //if x = 0xaa

=>x=0xaa;

case2:

int main() {
int x = 0;
WARN_IF(x == 0);
}

=>Warning: x == 0

除錯巨集

#define DBG_PRINTF(fmt, args...)\

printf("[%s,%d]" fmt, __FUNCTION__, __LINE__,##args)

int main()

{

DBG_PRINTF("Hello\n");

}

Note:

=>[main,7]Hello

除錯巨集的分級審查

#if DBG_LEVEL==0

#define PRINTF(fmt,...)

#else

#define PRINTF(fmt,...) printf(fmt,##__VA_ARGS__)

#endif

包裝:

利用參數來選擇呼叫的函式 #define test(x) test##x test1(){ printf("%s\n",__FUNCTION__); } test2(){ printf("%s\n",__FUNCTION__); } main(){ test(1)(); } Note: ##: 為連結運算子，CPP會將字元串作連結	=>test2
程式碼封裝(do while巨集定義) #define HELLO(str) do{\ printf("Hello:%s\n",str);\ }while(0) Note: 用do while封裝的意義在於，可以使巨集像函式一般使用而不會遇到一些狀況的編輯錯誤，如下: #define HELLO(str) printf("Hello:%s\n",str); main(){ if(condition) printf();;//多一個分號會視為if結構結束， //else被視為新的程式(沒有if) else printf() } test.c:9:2: error: ‘else’ without a previous ‘if’
將表格(cmd table)簡單化: #define COMMAND(name) {#name, name ## _command} struct command { char name; void (f)(void); } cmds[] = { COMMAND(quit), COMMAND(help), }; Note: #name: 為字串 "xxx"	展開=> struct command { char name; void (f)(void); } cmds[] = { {"quit", quit_command}, {"help", help_command}, };

功能:

在buffer中得到字串的大小 #define _STRING_LEN_GET(expr) sizeof #expr//stringize the expanded value("test.c") #define STRING_LEN_GET(expr) STRING_LEN_GET(expr) //展開為 main.c	int main() { char buf[128] = __FILE__; printf("%d\n",sizeof(buf)); printf("%d\n",STRING_LEN_GET(buf)); } => 128 4
round up/down #define ROUND_DOWN_TO_DIVISIBLE(num,div) \ ( (UINT32)(num) & -(UINT32)(div) ) #define ROUND_UP_TO_DIVISIBLE(num,div) \ ROUND_DOWN_TO_DIVISIBLE( (UINT32)(num) + (div) - 1, div )

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