实现自己的myprintf

最近看《C和指针》，里面讲到了可变参数如下图，所以就想自己实现一个myprintf

 

下面是实现的简单的myprintf.h

#include <stdarg.h>

#define NULL 0

va_list args;

char sign[] = { '0','1','2','3','4','5',
                '6','7','8','9','a','b',
                'c','d','e','f'};

void print_int( int num, int mode, int flag )
{
    if( num == 0 )
    {
        if( flag == 0 )
	{
	    putchar( '0' );
	    return;
	}
	else
	{
            return;
	}
    }

    print_int( num/mode, mode, 1 );
    
    putchar( sign[ num%mode ]  );
}

void print_str( char const *str )
{
    if( str == NULL )
    {
        return;
    }

    while( *str != '\0' )
    {
        putchar( *str );
	    str++;
    }
}


void print_float( float num )
{
    int part = num/1;

    print_int( part, 10, 0 );

    putchar( '.' );

    part=num*1000000-part*1000000;

    print_int( part, 10, 0 );
}

void check_type( char type )
{
    switch( type )
    {
        case 'd':
	{
	    int num = va_arg( args, int );

	    if( num < 0  )
	    {
	        putchar('-');
            num = num * (-1);
	    }

	    print_int( num, 10, 0 );
	    break;
	}

	case 'c':
	{
	    char ch = (char)va_arg( args, int );
	    putchar( ch );
	    break;
	}

	case 's':
	{
	    char *str = va_arg( args, char * );
	    print_str( str );
	    break;
	}

	case 'f':
	{
	    float num = (float)va_arg( args, double );

	    if( num < 0  )
	    {
	        putchar('-');
	    	num = num * (-1);
	    }

	    print_float( num );
	    break;
	}

	case 'p':
	{
	    int num = va_arg( args, int );
	    putchar( '0' );
	    putchar( 'x' );
        print_int( num, 16, 0 );
	    break;
	}

	default:
	{
	    putchar( '%' );
	    putchar( type );
	}
	       
    }
}

void myprintf( const char *format, ... )
{
    if( format == NULL )
    {
        return;
    }
    
    va_start( args, format );
    
    while( *format != '\0' )
    {
        while( *format != '%' && *format != '\0' )
	    {
	        putchar( *format );
            format++;	    
	    }

	if( *format != '\0' )
	{
	    format++;

	    if( *format != '\0' )
	    {
	        check_type( *format );
            format++;
	    }
	    else
	    {
	        putchar( *(format-1) );
	    }
	}
    }

    va_end( args );
}

把myprintf定义成用来调试代码的函数

debug.h

#include "myprintf.h"

#ifndef __DEBUG__
#define debug_msg(fmt, args...)
#else
#define debug_msg(fmt, args...) myprintf(fmt, ##args)
#endif

下面写个例子简单测试下

myprintf_test.c

#include "debug.h"

int main()
{
    int num = -5;
    char ch = 'a';
    char *str = "abcdef";
    char *ptr = NULL;
    float min = 0.1415926;
    
    printf("printf效果:\n\n");
    printf("num=%d,\\ch=%c,str=%s,\nmin=%f,str_addr=%p,ptr_addr=%p \
          \n",num,ch,str,min,str,ptr);
    
    myprintf("\nmyprintf的效果:\n\n");
    debug_msg("%%%num=%d,\\ch=%c,str=%s,\nmin=%f,str_addr=%p,ptr_addr=%p \
    \n%",num,ch,str,min,str,ptr);

    myprintf("\n");

    return 0;
}

运行一下

不知道为什么自带的printf不支持多个%%%的输出，转义也不行