Linux内核中的printf实现

11 #ifndef     __PRINT_H_
2 2 #define    __PRINT_H_
3 3 
4 4 void    print(char* fmt, ...);
5 5 void    printch(char ch);
6 6 void    printdec(int dec);
7 7 void    printflt(double flt);
8 8 void    printbin(int bin);
9 9 void    printhex(int hex);
1010 void    printstr(char* str);
1111 
1212 #define console_print(ch)    putchar(ch)
1313 
1414 #endif    /*#ifndef __PRINT_H_*/
15
16#include <stdio.h>
17  2 #include <stdarg.h>
18  3 #include "print.h"
19  4 
20  5 int main(void)
21  6 {
22  7     print("print: %c\n", 'c');
23  8     print("print %d\n", 1234567);
24  9     print("print: %f\n", 1234567.1234567);
25 10     print("print: %s\n", "string test");
26 11     print("print: %b\n", 0x12345ff);
27 12     print("print: %x\n", 0xabcdef);
28 13     print("print: %%\n");
29 14     return 0;
30 15 }
31 16 
32 17 void    print(char* fmt, ...)
33 18 {
34 19     double vargflt = 0;
35 20     int  vargint = 0;
36 21     char* vargpch = NULL;
37 22     char vargch = 0;
38 23     char* pfmt = NULL;
39 24     va_list vp;
40 25 
41 26     va_start(vp, fmt);
42 27     pfmt = fmt;
43 28 
44 29     while(*pfmt)
45 30     {
46 31         if(*pfmt == '%')
47 32         {
48 33             switch(*(++pfmt))
49 34             {
50 35                 
51 36                 case 'c':
52 37                     vargch = va_arg(vp, int); 
53 38                     /*    va_arg(ap, type), if type is narrow type (char, short, float) an error is given in strict ANSI
54 39                         mode, or a warning otherwise.In non-strict ANSI mode, 'type' is allowed to be any expression. */
55 40                     printch(vargch);
56 41                     break;
57 42                 case 'd':
58 43                 case 'i':
59 44                     vargint = va_arg(vp, int);
60 45                     printdec(vargint);
61 46                     break;
62 47                 case 'f':
63 48                     vargflt = va_arg(vp, double);
64 49                     /*    va_arg(ap, type), if type is narrow type (char, short, float) an error is given in strict ANSI
65 50                         mode, or a warning otherwise.In non-strict ANSI mode, 'type' is allowed to be any expression. */
66 51                     printflt(vargflt);
67 52                     break;
68 53                 case 's':
69 54                     vargpch = va_arg(vp, char*);
70 55                     printstr(vargpch);
71 56                     break;
72 57                 case 'b':
73 58                 case 'B':
74 59                     vargint = va_arg(vp, int);
75 60                     printbin(vargint);
76 61                     break;
77 62                 case 'x':
78 63                 case 'X':
79 64                     vargint = va_arg(vp, int);
80 65                     printhex(vargint);
81 66                     break;
82 67                 case '%':
83 68                     printch('%');
84 69                     break;
85 70                 default:
86 71                     break;
87 72             }
88 73             pfmt++;
89 74         }
90 75         else
91 76         {
92 77             printch(*pfmt++);
93 78         }
94 79     }
95 80     va_end(vp);
96 81 }
97 82 
98 83 void    printch(char ch)
99 84 {
100 85     console_print(ch);
101 86 }
102 87 
103 88 void    printdec(int dec)
104 89 {
105 90     if(dec==0)
106 91     {
107 92         return;
108 93     }
109 94     printdec(dec/10);
110 95     printch( (char)(dec%10 + '0'));
111 96 }
112 97 
113 98 void    printflt(double flt)
114 99 {
115100     int icnt = 0;
116101     int tmpint = 0;
117102     
118103     tmpint = (int)flt;
119104     printdec(tmpint);
120105     printch('.');
121106     flt = flt - tmpint;
122107     tmpint = (int)(flt * 1000000);
123108     printdec(tmpint);
124109 }
125110 
126111 void    printstr(char* str)
127112 {
128113     while(*str)
129114     {
130115         printch(*str++);
131116     }
132117 }
133118 
134119 void    printbin(int bin)
135120 {
136121     if(bin == 0)
137122     {
138123         printstr("0b");
139124         return;
140125     }
141126     printbin(bin/2);
142127     printch( (char)(bin%2 + '0'));
143128 }
144129 
145130 void    printhex(int hex)
146131 {
147132     if(hex==0)
148133     {
149134         printstr("0x");
150135         return;
151136     }
152137     printhex(hex/16);
153138     if(hex < 10)
154139     {
155140         printch((char)(hex%16 + '0'));
156141     }
157142     else
158143     {
159144         printch((char)(hex%16 - 10 + 'a' ));
160145     }
161146 }