printf实现c源码，很有参考价值

#include "jprintf.h" #include "stdarg.h" jprintf_char_FUN jprintf_char_p=0; //字符输出指针 //jprintf实现(格式字符串,参数列表)返回生成总长度 int jprintf(const char* jfmt,...) { //输出总长度 int jprint_len; //没有输出指针 if(jprintf_char_p==0)return 0; //没有数据 if(jfmt==0)return 0; //处理数据 { unsigned char c, f, r; unsigned long val; char s[16]; int i, w, cc; long val_sig; const char * jstr_p; va_list arp; va_start(arp, jfmt); jprint_len=0; cc=0; while(1) { jprint_len += cc; c = *jfmt++; if (c == 0) break; //结束跳出 //普通字符 if (c != '%') { jprintf_char_p(c); cc=1; continue; } w = 0; //宽度 f = 0; //格式 c = *jfmt++; //用0填充 if (c == '0') { f = 1; c = *jfmt++; } //计算对齐宽度 while (c >= '0' && c <= '9') { w = w * 10 + (c - '0'); c = *jfmt++; } //long型 if (c == 'l' || c=='L') { f |= 2; c = *jfmt++; } //数据类型 if (c == 's' || c == 'S') //字符串型 { jstr_p=(const char*)va_arg(arp,const char*); cc=0; while(*jstr_p) { jprintf_char_p(*jstr_p); jstr_p++; cc++; } continue; } else if (c == 'c' || c == 'C') //字符型 { jprintf_char_p(va_arg(arp, int)); //最小为int cc = 1; continue; } else if (c == 'd' || c =='D') //有符号整型 { r = 10; //10进制 if (f & 2) { //long val_sig=(long)va_arg(arp, long); if(val_sig<0) { val=0-val_sig; f |= 4; } else { val=val_sig; } } else { //int val_sig=(int)va_arg(arp, int); if(val_sig<0) { val=0-val_sig; f |= 4; } else { val=val_sig; } } } else if (c == 'u' || c == 'U') //无符号整型 { r = 10; //10进制 if (f & 2) { //long val=(unsigned long)va_arg(arp, unsigned long); } else { //int val=(unsigned int)va_arg(arp, unsigned int); } } else if (c == 'x' || c == 'X') //十六进制 { r = 16; //16进制 if (f & 2) { //long val=(unsigned long)va_arg(arp, unsigned long); } else { //int val=(unsigned int)va_arg(arp, unsigned int); } if (c == 'x')f = f | 8; //小写 } else if (c == '%') //%号 { jprintf_char_p('%'); break; } else //未知类型 { break; } //数值转换 i = sizeof(s) - 1; s[i] = 0; //防止溢出 do { c = (unsigned char)(val % r + '0');//r代表进制 if (c > '9') { c += (f & 8)?39:7; //十六进制 } s[--i] = c; //从后面开始保存 val /= r; } while (i && val); //负数 if (i && (f & 4)) s[--i] = '-'; //填充 w = sizeof(s) - 1 - w; while (i && i > w) s[--i] = (f & 1) ? '0' : ' '; //输出 jstr_p=&s[i]; cc=0; while(*jstr_p) { jprintf_char_p(*jstr_p); jstr_p++; cc++; } continue; } va_end(arp); } return jprint_len; } //打印十六进制文本(缓存,长度,末尾结束字符串如:"\r\n") void jprint_hex(volatile unsigned char *jbuf, unsigned int jprint_len,const char * jend_str) { unsigned int i; unsigned char jt_val; for(i=0;i<jprint_len;i++) { jt_val=*(jbuf+i); jprintf("%02X ",jt_val); } if(jend_str)jprintf("%s",jend_str); }