C - GetInt: Perform free-format input conversion by breaking a stream of characters into integer

女爷i 2022-11-06 07:00 7阅读 0赞

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/*
     * GetInt: Perform free-format input conversion by breaking a stream of characters
     * into integer values, one integer per call.
     *
     * GetInt.c - by FreeMan
     */
    
    #include <ctype.h>
    #include <stdio.h>
    
    #define BUFFERLENGTH 100
    
    int GetCh(void);
    void UngetCh(int);
    
    int buf[BUFFERLENGTH];
    int nfp = 0;
    
    void ViewBuffer(void)
    {
    	int i;
    	printf("\nbuffer:\n");
    	for (i = nfp - 1; i >= 0; i--)
    	{
    		printf("%d\n", buf[i]);
    	}
    }
    
    int GetCh(void)
    {
    	return (nfp > 0) ? buf[--nfp] : getchar();
    }
    
    void UngetCh(int c)
    {
    	if (nfp < BUFFERLENGTH)
    	{
    		buf[nfp++] = c;
    	}
    	else
    	{
    		printf("error: ungetch buffer overflow\n");
    	}
    }
    
    int GetInt(int *pn)
    {
    	int c, sign;
    	while (isspace(c = getchar()))
    		;
    	if (!isdigit(c) && c != EOF && c != '+' && c != '-')
    	{
    		UngetCh(c);
    		return 0;
    	}
    	sign = (c == '-') ? -1 : 1;
    	if (c == '+' || c == '-')
    	{
    		c = GetCh();
    		if (!isdigit(c))
    		{
    			UngetCh(sign == -1 ? '-' : '+');
    			return 0;
    		}
    	}
    	for (*pn = 0; isdigit(c); c = GetCh())
    	{
    		*pn = *pn * 10 + (c - '0');
    	}
    	*pn *= sign;
    	if (c != EOF)
    	{
    		UngetCh(c);
    	}
    	return c;
    }
    
    int main()
    {
    	int x, retval, * px;
    	px = &x;
    	retval = GetInt(px);
    	printf("retval = %d, x = %d\n", retval, x);
    	ViewBuffer();
    	return 0;
    }
    
    // Input:
    /*
       -123456
    */
    
    // Output:
    /*
    retval = 10, x = -123456
    
    buffer:
    10
    
    */

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