實現格式化輸出

代碼如下：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>

void ShowMessage(char *,const char *,...);

int main(void)
{
    ShowMessage("123.txt","%d %s %x %04X\n",100,"hello",107,107);
    return 0;
}

void ShowMessage(char *name,const char *format,...)  
{ 
    union {
        int a;
        float b;
        char *c;
    }ret;
    va_list arg_list;  
    char cmd[10]={0};
    int i=0; 
    va_start(arg_list, format);  
    const char *start = format;  
    FILE *lfp = fopen(name,"a+");  
    for(;*start != '\0';start++){
        if (*start == '%'){  
            for(i=0;;i++,start++){
                cmd[i]=*start;  
                switch (*start){  
                    case 's':  
                        ret.c = va_arg(arg_list, char *);   
                        fputs(ret.c, lfp);  
                        break;  
                    case 'd':     
                    case 'u':
                    case 'x':  
                    case 'X':  
                        ret.a = va_arg(arg_list,int);  
                        fprintf(lfp,cmd,ret.a);  
                        break;  
                    case 'f':
                        ret.b = va_arg(arg_list,int);  
                        fprintf(lfp,cmd,ret.b);  
                        break;
                }
                if(*start=='s'||*start=='d'||*start=='x'||*start=='X'||*start=='u'||*start=='f')
                    break;
            }
            memset(cmd,0,10); 
        }else{
            putc(*start,lfp);  
        }
    }  
    va_end(arg_list);  
    fclose(lfp);  
}