本帖最后由 wuhenyouyu 于 2015-9-25 10:58 编辑
看了下论坛里的前辈关于单片机裸编的程序架构的谈论,我最近也正好在思考这个问题,所以读了一些资料,有位前辈说的好:一切延时都是编程的敌人。我感觉裸编就是要消除延时等待和做好条件触发。欢迎大家谈论。
对于‘##’的理解:
这个就是字符串拼接,A##B,它就是简单的把A和B拼接在一起。如果A和B都表示宏,也不再展开。
#define A 01
#define B 02
#define concat(S1,S2) S1##S2
#concat1(s1,s2) concat(s1,s2)
concat(A,B)->A##B->AB 不再进行宏替代。
concat1(A,B)在VS2010下得到的结果是0102,我感觉过程如下:
concat1(A,B)->concat(A,B)->concat(01,02)->01##02->0102
又看了C99标准,在6.10.3.5,156页有个例子:
EXAMPLE 4 To illustrate the rules for creating character string literals and concatenating tokens, the
sequence
#define str(s) # s
#define xstr(s) str(s)
#define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \
x ## s, x ## t)
#define INCFILE(n) vers ## n // from previous #include example
#define glue(a, b) a ## b
#define xglue(a, b) glue(a, b)
#define HIGHLOW "hello"
#define LOW LOW ", world"
debug(1, 2);
fputs(str(strncmp("abc\0d", "abc", '\4') // this goes away
== 0) str(: @\n), s);
#include xstr(INCFILE(2).h)
glue(HIGH, LOW);
xglue(HIGH, LOW);
results in:
printf("x" "1" "= %d, x" "2" "= %s", x1, x2);
fputs(
"strncmp(\"abc\\0d\", \"abc\", '\\4') == 0" ": @\n",
s);
#include "vers2.h" (after macro replacement, before file access)
"hello";
"hello" ", world"
or, after concatenation of the character string literals,
printf("x1= %d, x2= %s", x1, x2);
fputs(
"strncmp(\"abc\\0d\", \"abc\", '\\4') == 0: @\n",
s);
#include "vers2.h" (after macro replacement, before file access)
"hello";
"hello, world"
首先分析:glue(HIGH, LOW);结果为"hello";
glue(HIGH, LOW)->HIGH ## LOW->HIGHLOW->"hello";
再分析:xglue(HIGH, LOW)结果"hello, world"
xglue(HIGH, LOW)->glue(HIGH,LOW)->glue(HIGH,LOW ", world")->HIGH ## LOW ", world"->HIGHLOW ", world"->"hello"", world"->"hello, world"
上面是宏有外而内替换,好像C99并没有规定宏替换顺序,只是说遇到#和##不在宏展开。VS2010符合这个原则。
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