转载自：http://blog.csdn.net/xfeng88/article/details/6695848
在嵌入式开发中，常常会通过串口打印一些信息到PC终端，这就需要实现自己的printf函数，下面介绍打印函数print的实现。
print.h
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_*/
上面print函数为全功能的打印函数，可以实现类似printf的功能，printch实现单个字符的打印、printdec实现十进制格式数字的打印，printflt实现浮点数的打印，printbin实现二进制格式数字的打印，printhex实现十六进制格式数字的打印，printstr实现字符串的打印，console_print函数是串口单字符打印函数的宏定义，这里暂时用PC终端单字符打印函数putchar代替。在实际嵌入式环境下，替换成串口单字符打印函数即可。
print.c
1 #include <stdio.h> 2 #include <stdarg.h> 3 #include "print.h" 4 5 int main(void) 6 { 7 print("print: %c ", 'c'); 8 print("print %d ", 1234567); 9 print("print: %f ", 1234567.1234567); 10 print("print: %s ", "string test"); 11 print("print: %b ", 0x12345ff); 12 print("print: %x ", 0xabcdef); 13 print("print: %% "); 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 }