基本编程元素用到的技巧

当你想了解一个函数（或方法）在做什么，你可以如下策略：

• 根据函数名猜测
• 阅读函数头的注释
• 分析函数是如何被使用
• 阅读函数体內的代码
• 查询外部程序文档
• 养成碰到库函数就阅读文档的习惯（传送门如何查看函数）

注释是重点啊啊啊！强行观看，下面上“热腾腾”开源代码

      <span style="font-size:18px;">  /*<span style="color: rgb(255, 0, 0);">返回值储存于整型变量中</span>*/while ((<span style="color: rgb(255, 0, 0);">c</span> = getopt (argc, argv, "t:")) != -1) {switch (c) {case 't':getstops(optarg);break;                /*<span style="color: rgb(255, 0, 0);">二者共用一段代码</span>*/case '?':default:usage();/* NOTREACHED */}}</span>

<span style="font-size:18px;">        case 'a':fts_options |= FTS_SEEDOT;/* <span style="color:#ff0000;">FALLTHROUGH </span>                        <span style="color:#ff0000;">没有break，return，continue时，用一条注释进行说明.接着判断'</span><span style="color: rgb(255, 0, 0); font-family: SimSun;">A'</span>                        */case 'A':f_listdot = 1;break</span>

<span style="font-size:18px;">        case BATCH:writefile(time(NULL), 'b');break;        /*<span style="color:#ff0000;">捕获产生意外值的程序错误提醒程序维护者</span>*/default:panic("Internal error");break;</span>

<span style="font-size:18px;">    while ((c = getchar()) != EOF) {                        /*<span style="color:#ff0000;">switch语句用作程序字符处理循环的一部分</span>*/switch (c) {case '\t':if (nstops == 0) {do {putchar(' ');column++;} while (column & 07);continue;}if (nstops == 1) {do {putchar(' ');column++;} while (((column - 1) % tabstops[0]) != (tabstops[0] - 1));continue;}for (n = 0; n < nstops; n++)if (tabstops[n] > column)break;if (n == nstops) {putchar(' ');column++;continue;}while (column < tabstops[n]) {putchar(' ');column++;}continue;case '\b':if (column)column--;putchar('\b');continue;                        /*<span style="color:#ff0000;">所有其他字符*</span>/default:putchar(c);column++;continue;case '\n':putchar(c);column = 0;continue;}}} while (argc > 0);exit(0);}</span>

<span style="font-size:18px;">if ((<span style="color:#ff0000;">dd = opendir(dir)) == NULL)</span>return (CC_ERROR);words = sl_init();        /*<span style="color:#ff0000;">循环处理库函数返回的结果集</span>*/for (<span style="color:#ff0000;">dp = readdir(dd); dp != NULL; dp = readdir(dd)</span>)</span>

<span style="font-size:18px;"><span style="color:#ff0000;">for (cnt = 1, t = p; cnt <= cnt_orig; ++t, ++cnt)</span> {t->lno = lno;t->coff = 0;t->soff = cnt;SMAP_FLUSH(t);if (vs_line(sp, t, NULL, NULL))return (1);} </span>

<span style="font-size:18px;">voidtransition(s)state_t s;{    /*<span style="color:#ff0000;">无限循环控制所有的unix进程     在大多的情况下，无限循环用来表达循环开始或结束时退出条件无法确定的循环     return，break，exit退出</span>     */     for (;;) {s = (state_t) (*s)();#ifndef LETS_GET_SMALLquiet = 0;#endif}}</span>

<span style="font-size:18px;">static voidgetstops(cp)char *cp;{int i;nstops = 0;for (;;) {i = 0;               /*将字符串转换为数字*/while (*cp >= '0' && *cp <= '9')i = i * 10 + *cp++ - '0';/*<span style="color:#ff0000;">德摩根法则解开复杂的逻辑表达式*</span>/if (i <= 0 || i > 256) {                /*<span style="color:#ff0000;">抱怨不合理的说明</span>*/bad:fprintf(stderr, "Bad tab stop spec\n");exit(1);}/*<span style="color:#ff0000;">短路求值*</span>/if (nstops > 0 && i <= tabstops[nstops-1])goto bad;tabstops[nstops++] = i;/*<span style="color:#ff0000;">跳出循环，局部重构*</span>/        if (*cp == 0)break;else if (*cp != ',' && *cp != ' ')goto bad;        elsecp++;}}</span>

<span style="font-size:18px;">/*<span style="color:#ff0000;">短路求值，只有t ＝= NULL时，才计算t->type的值*</span>/if (t != NULL && t->type != TEOF && interactive && really_exit)</span>

<span style="font-size:18px;">/*<span style="color:#ff0000;">移位运算符计算</span>*/    n = ((dp - cp) << 2) + 1; /* 4 times + NULL */</span>

<span style="font-size:18px;">intatmresolve(rt, m, dst, desten)register struct rtentry *rt;struct mbuf *m;register struct sockaddr *dst;/*<span style="color:#ff0000;">有时也用标有in或out的注释来标记引用参数*/</span>register struct atm_pseudohdr *desten;/<span style="color:#ff0000;">* OUT *</span>/{</span>

</pre><pre name="code" class="cpp"><span style="font-size:18px;"></span>

<span style="font-size:18px;">     /*<span style="color: rgb(255, 0, 0);">初始化栈</span>*/stackp = de_stack;while ((code = getcode(zs)) > -1) {if ((code == CLEAR) && block_compress) {for (code = 255; code >= 0; code--)tab_prefixof(code) = 0;clear_flg = 1;free_ent = FIRST - 1;if ((code = getcode(zs)) == -1)/* O, untimely death! */break;}incode = code;/* Special case for KwKwK string. */if (code >= free_ent) {                        /*<span style="color: rgb(255, 0, 0);">将finchar压栈*</span>/*stackp++ = finchar;code = oldcode;}/* Generate output characters in reverse order. */while (code >= 256) {*stackp++ = tab_suffixof(code);code = tab_prefixof(code);}*stackp++ = finchar = tab_suffixof(code);/* And put them out in forward order.  */middle:do {if (count-- == 0)return (num);                        /*<span style="color: rgb(255, 0, 0);">将栈顶内容弹到*bp中</span>*/*bp++ = *--stackp;          } /*<span style="color: rgb(255, 0, 0);">检查栈是否为空*</span>/        while (stackp > de_stack);</span><pre name="code" class="cpp" style="font-size: 18px;">利用指针方式访问基于数组的栈

<span style="font-size:18px;">char *inet_ntoa(ad)  struct in_addr ad;{  unsigned long int s_ad;  int a, b, c, d;  /*<span style="color:#ff0000;">防止返回的数组的内存空间被重写*</span>/  static char addr[20];    s_ad = ad.s_addr;  d = s_ad % 256;  s_ad /= 256;  c = s_ad % 256;  s_ad /= 256;  b = s_ad % 256;  a = s_ad / 256;  sprintf(addr, "%d.%d.%d.%d", a, b, c, d);    return addr;}</span>