C语言常用方法技巧
html,body,div,span,applet,object,iframe,h1,h2,h3,h4,h5,h6,p,blockquote,pre,a,abbr,acronym,address,big,cite,code,del,dfn,em,img,ins,kbd,q,s,samp,small,strike,strong,sub,sup,tt,var,b,u,i,center,dl,dt,dd,ol,ul,li,fieldset,form,label,legend,table,caption,tbody,tfoot,thead,tr,th,td,article,aside,canvas,details,embed,figure,figcaption,footer,header,hgroup,menu,nav,output,ruby,section,summary,time,mark,audio,video { margin: 0; padding: 0; border: 0 }body { font-family: Helvetica, arial, freesans, clean, sans-serif; font-size: 14px; line-height: 1.6; color: #333; background-color: #fff; padding: 20px; max-width: 960px; margin: 0 auto }body>*:first-child { margin-top: 0 !important }body>*:last-child { margin-bottom: 0 !important }p,blockquote,ul,ol,dl,table,pre { margin: 15px 0 }h1,h2,h3,h4,h5,h6 { margin: 20px 0 10px; padding: 0; font-weight: bold }h1 tt,h1 code,h2 tt,h2 code,h3 tt,h3 code,h4 tt,h4 code,h5 tt,h5 code,h6 tt,h6 code { font-size: inherit }h1 { font-size: 28px; color: #000 }h2 { font-size: 24px; border-bottom: 1px solid #ccc; color: #000 }h3 { font-size: 18px }h4 { font-size: 16px }h5 { font-size: 14px }h6 { color: #777; font-size: 14px }body>h2:first-child,body>h1:first-child,body>h1:first-child+h2,body>h3:first-child,body>h4:first-child,body>h5:first-child,body>h6:first-child { margin-top: 0; padding-top: 0 }a:first-child h1,a:first-child h2,a:first-child h3,a:first-child h4,a:first-child h5,a:first-child h6 { margin-top: 0; padding-top: 0 }h1+p,h2+p,h3+p,h4+p,h5+p,h6+p { margin-top: 10px }a { color: #4183C4; text-decoration: none }a:hover { text-decoration: underline }ul,ol { padding-left: 30px }ul li>:first-child,ol li>:first-child,ul li ul:first-of-type,ol li ol:first-of-type,ul li ol:first-of-type,ol li ul:first-of-type { margin-top: 0px }ul ul,ul ol,ol ol,ol ul { margin-bottom: 0 }dl { padding: 0 }dl dt { font-size: 14px; font-weight: bold; font-style: italic; padding: 0; margin: 15px 0 5px }dl dt:first-child { padding: 0 }dl dt>:first-child { margin-top: 0px }dl dt>:last-child { margin-bottom: 0px }dl dd { margin: 0 0 15px; padding: 0 15px }dl dd>:first-child { margin-top: 0px }dl dd>:last-child { margin-bottom: 0px }pre,code,tt { font-size: 12px; font-family: Consolas, “Liberation Mono”, Courier, monospace }code,tt { margin: 0 0px; padding: 0px 0px; white-space: nowrap; border: 1px solid #eaeaea; background-color: #f8f8f8 }pre>code { margin: 0; padding: 0; white-space: pre; border: none; background: transparent }pre { background-color: #f8f8f8; border: 1px solid #ccc; font-size: 13px; line-height: 19px; overflow: auto; padding: 6px 10px }pre code,pre tt { background-color: transparent; border: none }kbd { background-color: #DDDDDD; background-image: linear-gradient(#F1F1F1, #DDDDDD); background-repeat: repeat-x; border-color: #DDDDDD #CCCCCC #CCCCCC #DDDDDD; border-style: solid; border-width: 1px; font-family: “Helvetica Neue”, Helvetica, Arial, sans-serif; line-height: 10px; padding: 1px 4px }blockquote { border-left: 4px solid #DDD; padding: 0 15px; color: #777 }blockquote>:first-child { margin-top: 0px }blockquote>:last-child { margin-bottom: 0px }hr { clear: both; margin: 15px 0; height: 0px; overflow: hidden; border: none; background: transparent; border-bottom: 4px solid #ddd; padding: 0 }table th { font-weight: bold }table th,table td { border: 1px solid #ccc; padding: 6px 13px }table tr { border-top: 1px solid #ccc; background-color: #fff }table tr:nth-child(2n) { background-color: #f8f8f8 }img { max-width: 100% }除法向上取整
#define DIV_ROUND_UP(n, d) (((n)+(d)-1) / (d))大端小端选择
low-endian or high-endian
typedef union {short W;/* Word access */struct {/* Byte access */#ifdef LOW_ENDIANbyte low, high;/* in low-endian arch */#elsebyte high, low;/* in high-endian arch */#endif} B;} word;求余数运算
a = a % 8;=>a = a & 7;说明：位运算只需一个指令周期；取余通常需要调用子程序。平方运算
a = pow(a, 2.0);=>a = a * a;说明：内置乘法运算器的处理器中，乘法运算比求平方运算更快；即使没有内置乘法运算器，乘法运算的子程序也比平方运算子程序效率高。移位实现乘除法运算
a = a * 4;b = b / 4;=>a = a << 2;b = b >> 2;说明：通常乘以或者除以2n，可使用移位方法代替。a = a * 9;=>a = (a << 3) + a;while 循环和 do…while 循环
说明：do...while 循环编译后生成的代码长度短于 while 循环。重定义类型，扩展移植性
typedef unsigned char boolean; /* Boolean value type. */typedef unsigned long int uint32; /* Unsigned 32 bit value */typedef unsigned short uint16; /* Unsigned 16 bit value */typedef unsigned char uint8; /* Unsigned 8 bit value */typedef signed long int int32; /* Signed 32 bit value */typedef signed short int16; /* Signed 16 bit value */typedef signed char int8; /* Signed 8 bit value */得到指定地址上的一个字节或字
typedef unsigned char byte; /* Unsigned 8 bit value type */ typedef unsigned short word; /* Unsigned 16 bit value type */#define MEM_B(x) (*((byte*)(x)))#define MEM_W(x) (*((word*)(x)))求取极值
#define MAX(x, y) ((x) > (y) ? (x) : (y))#define MIN(x, y) ((x) < (y) ? (x) : (y))得到一个 field 在结构体(struct)中的偏移量
typedef unsigned long dword; /* Unsigned 32 bit value type */#define FPOS(type, field)\ ( (dword)&((type*)0)->field )得到一个结构体中 field 所占用的字节数
#define FSIZE(type, field)\ ( sizeof(((type*)0)->field) )按照 LSB 格式把一个 word(16 bit) 转换成两个字节
#define FLOPW(ray, val)\ do {\ (ray)[0] = ((val)>>8);\ (ray)[1] = ((val)&0xFF);\ }while(0);得到一个变量的地址
typedef unsigned char byte; /* Unsigned 8 bit value type */typedef unsigned short word; /* Unsigned 16 bit value type */ #define B_PTR(var) ((byte*)(void*)&(var))#define W_PTR(var) ((word*)(void*)&(var))得到一个字节的低位和高位
typedef unsigned char byte; /* Unsigned 8 bit value type */typedef unsigned short word; /* Unsigned 16 bit value type */#define WORD_L(var) ((byte)(word)(var)&(0xFF))#define WORD_H(var) ((byte)(word)(var)>>(8))返回一个比 X 大的接近 8 的倍数
#define RND8(x) ((((x) + 7) >> 3) << 3) 防止溢出的方法
#define INC_SAT(val)\ ((val) = ( ((val) + 1) > (val)) ? ((val) + 1):(val) )返回数组元素的个数
#define ARR_SIZE(a)\ ( (sizeof(a)) / (sizeof(a[0])) )返回一个无符号数的后 n 位数
typedef unsigned long dword; /* Unsigned 32 bit value type */ #define MOD_BY_POWER_OF_TWO(val, mod_by)\ ((dword)(val)&(dword)(2<<(mod_by) - 1))IO 空间映射在存储空间中的结构
typedef unsigned char byte; /* Unsigned 8 bit value type */typedef unsigned short word; /* Unsigned 16 bit value type */typedef unsigned long dword; /* Unsigned 32 bit value type */#define outp(port) (*((volatile byte *)(port)))#define outpw(port) (*((volatile word *)(port)))#define outpdw(port) (*((volatile dword *)(port)))#define inp(port, val) (*((volatile byte *)(port))) = (byte)(val)#define inpw(port, val) (*((volatile word *)(port))) = (word)(val)#define inpdw(port, val) (*((volatile dword *)(port))) = (dword)(val)宏中 “#” 和 “##” 的用法
一、使用 "#" 把宏参数变为一个字符串， 用 "##" 把两个宏参数贴合在一起。 #define STR(val) (#val) #define CONS(a, b) (int)(a##e##b) -> STR(hello) ==> "hello" CONS(2, 3) ==> 2000 // 2e3二、当宏参数是另一个宏的时候 需要注意的是凡宏定义里有用 '#' 或 '##' 的地方宏参数是不会再展开. 1, 非 '#' 和 '##' 的情况 #define TOW (2) #define MUL(a,b) (a*b) printf("%d*%d=%d\n", TOW, TOW, MUL(TOW,TOW)); ==> printf("%d*%d=%d\n", (2), (2), ((2)*(2))); MUL里的参数TOW会被展开为(2)。 2, 当有 '#' 或 '##' 的时候 #define A (2) #define STR(s) #s #define CONS(a,b) int(a##e##b) printf("int max: %s\n", STR(INT_MAX)); // INT_MAX #include ==> printf("int max: %s\n", "INT_MAX"); printf("%s\n", CONS(A, A)); // compile error ==> printf("%s\n", int(AeA)); INT_MAX和A都不会再被展开, 然而解决这个问题的方法很简单，加多一层中间转换宏， 加这层宏的用意是把所有宏的参数在这层里全部展开, 那么在转换宏里的那一个 宏(_STR)就能得到正确的宏参数. #define A (2) #define _STR(s) (#s) #define STR(s) _STR(s) // 转换宏 #define _CONS(a,b) int(a##e##b) #define CONS(a,b) _CONS(a,b) // 转换宏 printf("int max: %s\n", STR(INT_MAX)); // INT_MAX,int型的最大值，为一个变量 #include 输出为: int max: 0x7fffffff STR(INT_MAX) --> _STR(0x7fffffff) 然后再转换成字符串; printf("%d\n", CONS(A, A)); 输出为：200 CONS(A, A) --> _CONS((2), (2)) --> int((2)e(2))三、'#' 和 '##' 的一些应用特例 1、合并匿名变量名 #define ___ANONYMOUS1(type, var, line) type var##line #define __ANONYMOUS0(type, line) ___ANONYMOUS1(type, _anonymous, line) #define ANONYMOUS(type) __ANONYMOUS0(type, __LINE__) 例：ANONYMOUS(static int); 即: static int _anonymous70; 70表示该行行号; 第一层：ANONYMOUS(static int); --> __ANONYMOUS0(static int, __LINE__); 第二层： --> ___ANONYMOUS1(static int, _anonymous, 70); 第三层： --> static int _anonymous70; 即每次只能解开当前层的宏，所以__LINE__在第二层才能被解开; 2、填充结构 #define FILL(a) {a, #a} enum IDD {OPEN, CLOSE}; typedef struct MSG{ IDD id; const char * msg; }MSG; MSG _msg[] = {FILL(OPEN), FILL(CLOSE)}; ==> MSG _msg[] = {{OPEN, "OPEN"}, {CLOSE, "CLOSE"}}; 3、记录文件名 #define _GET_FILE_NAME(f) #f #define GET_FILE_NAME(f) _GET_FILE_NAME(f) static char FILE_NAME[] = GET_FILE_NAME(__FILE__); 4、得到一个数值类型所对应的字符串缓冲大小 #define _TYPE_BUF_SIZE(type) sizeof #type #define TYPE_BUF_SIZE(type) _TYPE_BUF_SIZE(type) char buf[TYPE_BUF_SIZE(INT_MAX)]; --> char buf[_TYPE_BUF_SIZE(0x7fffffff)]; --> char buf[sizeof "0x7fffffff"]; 这里相当于： char buf[11];关于平方根倒数速算法（雷神之锤3，牛B）每个人的生命都是可以绽放美丽，只要你珍惜。
