Linux内核中的printf实现

1 #ifndef     __PRINT_H_
 2 #define    __PRINT_H_
 3 
 4 void    print(char* fmt, ...);
 5 void    printch(char ch);
 6 void    printdec(int dec);
 7 void    printflt(double flt);
 8 void    printbin(int bin);
 9 void    printhex(int hex);
10 void    printstr(char* str);
11 
12 #define console_print(ch)    putchar(ch)
13 
14 #endif    /*#ifndef __PRINT_H_*/

 #include <stdio.h>
  2 #include <stdarg.h>
  3 #include "print.h"
  4 
  5 int main(void)
  6 {
  7     print("print: %c\n", 'c');
  8     print("print %d\n", 1234567);
  9     print("print: %f\n", 1234567.1234567);
 10     print("print: %s\n", "string test");
 11     print("print: %b\n", 0x12345ff);
 12     print("print: %x\n", 0xabcdef);
 13     print("print: %%\n");
 14     return 0;
 15 }
 16 
 17 void    print(char* fmt, ...)
 18 {
 19     double vargflt = 0;
 20     int  vargint = 0;
 21     char* vargpch = NULL;
 22     char vargch = 0;
 23     char* pfmt = NULL;
 24     va_list vp;
 25 
 26     va_start(vp, fmt);
 27     pfmt = fmt;
 28 
 29     while(*pfmt)
 30     {
 31         if(*pfmt == '%')
 32         {
 33             switch(*(++pfmt))
 34             {
 35                 
 36                 case 'c':
 37                     vargch = va_arg(vp, int); 
 38                     /*    va_arg(ap, type), if type is narrow type (char, short, float) an error is given in strict ANSI
 39                         mode, or a warning otherwise.In non-strict ANSI mode, 'type' is allowed to be any expression. */
 40                     printch(vargch);
 41                     break;
 42                 case 'd':
 43                 case 'i':
 44                     vargint = va_arg(vp, int);
 45                     printdec(vargint);
 46                     break;
 47                 case 'f':
 48                     vargflt = va_arg(vp, double);
 49                     /*    va_arg(ap, type), if type is narrow type (char, short, float) an error is given in strict ANSI
 50                         mode, or a warning otherwise.In non-strict ANSI mode, 'type' is allowed to be any expression. */
 51                     printflt(vargflt);
 52                     break;
 53                 case 's':
 54                     vargpch = va_arg(vp, char*);
 55                     printstr(vargpch);
 56                     break;
 57                 case 'b':
 58                 case 'B':
 59                     vargint = va_arg(vp, int);
 60                     printbin(vargint);
 61                     break;
 62                 case 'x':
 63                 case 'X':
 64                     vargint = va_arg(vp, int);
 65                     printhex(vargint);
 66                     break;
 67                 case '%':
 68                     printch('%');
 69                     break;
 70                 default:
 71                     break;
 72             }
 73             pfmt++;
 74         }
 75         else
 76         {
 77             printch(*pfmt++);
 78         }
 79     }
 80     va_end(vp);
 81 }
 82 
 83 void    printch(char ch)
 84 {
 85     console_print(ch);
 86 }
 87 
 88 void    printdec(int dec)
 89 {
 90     if(dec==0)
 91     {
 92         return;
 93     }
 94     printdec(dec/10);
 95     printch( (char)(dec%10 + '0'));
 96 }
 97 
 98 void    printflt(double flt)
 99 {
100     int icnt = 0;
101     int tmpint = 0;
102     
103     tmpint = (int)flt;
104     printdec(tmpint);
105     printch('.');
106     flt = flt - tmpint;
107     tmpint = (int)(flt * 1000000);
108     printdec(tmpint);
109 }
110 
111 void    printstr(char* str)
112 {
113     while(*str)
114     {
115         printch(*str++);
116     }
117 }
118 
119 void    printbin(int bin)
120 {
121     if(bin == 0)
122     {
123         printstr("0b");
124         return;
125     }
126     printbin(bin/2);
127     printch( (char)(bin%2 + '0'));
128 }
129 
130 void    printhex(int hex)
131 {
132     if(hex==0)
133     {
134         printstr("0x");
135         return;
136     }
137     printhex(hex/16);
138     if(hex < 10)
139     {
140         printch((char)(hex%16 + '0'));
141     }
142     else
143     {
144         printch((char)(hex%16 - 10 + 'a' ));
145     }
146 }