code:printf - ikarishinjieva/unixV6-code-analyze-chs GitHub Wiki

2329

2330 /*

2331  * Scaled down version of C library printf.

2332  * Only %s %l %d (==%l) %o are recognized.

2333  * Used to print diagnostic information

2334  * directly on console tty.

2335  * Since it is not interrupt driven,

2336  * all system activities are pretty much

2337  * suspended.

2338  * Printf should not be used for chit-chat.

2339  */

2340 printf(fmt,x1,x2,x3,x4,x5,x6,x7,x8,x9,xa,xb,xc)

2341 char fmt[];

2342 {

2343     register char *s;

2344     register *adx, c;

2345

2346     adx = &x1;

以下开始扫描格式串，并逐一转换输出

2347 loop:

2348     while((c = *fmt++) != ’%’) {

2349          if(c == ’\0’)

2350          return

2351     putchar(c);

2352 }

• 若当前扫描的字符并非保留字，则直接输出
• 若格式串读到末尾(\0)，则函数返回
• 当读到格式保留字时，往下执行

2353     c = *fmt++;

2354     if(c == ’d’ || c == ’l’ || c == ’o’)

2355          printn(*adx, c==’o’? 8: 10);

• 转换并输出数字格式
• 2355判断输出八进制或十进制数

2356     if(c == ’s’) {

2357          s = *adx;

2358          while(c = *s++)

2359           putchar(c);

2360     }

• 输出字符串

2361     adx++;

2362     goto loop;

• 返回2347，进行下一次扫描

2363 }

2364 /* -------------------------*/

• code:main
• code:panic
• code:prdev
• code:deverror
• code:trap
• code:falloc
• code:iget