Numeric Checking in C++

**Raptor2150** · 01-20-2002, 02:03 AM

I'm looking for something along the guidelines of IsNumeric() in VB for C++. Yeah, I'm a vb programmer

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**dighn** · 01-20-2002, 05:44 AM

.

EDIT: don't know (sorry)

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Keep it brief

[This message has been edited by dighn (edited January 20, 2002).]

**Galen of Edgewood** · 01-20-2002, 09:51 AM

Originally posted by Raptor2150:
I'm looking for something along the guidelines of IsNumeric() in VB for C++. Yeah, I'm a vb programmer

What is it that you are trying to accomplish? We might be able to code somethin' for ya.

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**Raptor2150** · 01-20-2002, 03:35 PM

Wow, is it really that difficult in c? I just wanted to check if an inputted variable of type float was actually a numeric value before I tried to do any calculations...

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**dighn** · 01-20-2002, 05:58 PM

well u could alwasy write one yourself...

this code will make sure the string is in the format -x.x where - . are optional and x can be any number of digits as long as it's at least 1 digit. this is just sort of a demo so there's lots of room for improvement

Code:

bool isNumeric(const char* s)
{
  bool needDigit = true;
  bool gotDecimal = false;

  for(int i = 0; i &lt; strlen(s);i++)
  {
    if(s[i] &lt; '0' &#0124; &#0124; s[i] &gt; '9')
    {
      if(s[i] == '-')
      {
		if(i != 0)
          return false;
      }
      else if(s[i] == '.')
      {
		if(needDigit)
          return false;
        if(gotDecimal)
          return false;
        needDigit = true;
        gotDecimal = true;
      }
      else
        return false;
    }
	else
		needDigit = false;
  }
  return !needDigit;
}

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Keep it brief

**Conrad Song** · 01-20-2002, 11:57 PM

Originally posted by Raptor2150:
I'm looking for something along the guidelines of IsNumeric() in VB for C++. Yeah, I'm a vb programmer

The easiest way is to convert the string to a number using scanf:

Code:

char buffer[256] = "-10";
int num;
sscanf(buffer, "%d", &num);

The trick is that scanf will return the number of arguments that it successfully assigned. Thus:

Code:

if( sscanf(buffer, "%d", &num) != 1 ) {
   /* error here */
}

**Raptor2150** · 01-21-2002, 04:01 PM

Wow, is it really that complicated? I would think that there would be some sort of function for it. Anyways, thanks all.

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**Strogian** · 01-21-2002, 06:21 PM

Yep, C(++) doesn't always provide every little thing that people may want. But, that's why you make your own functions, then it is no longer complicated. ... as long as you have good comments.

**schnarf283** · 01-23-2002, 12:19 AM

Uh, if(!isalpha(stuff)), or is that only PHP or something?

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**Conrad Song** · 01-23-2002, 02:22 AM

Originally posted by schnarf283:
Uh, if(!isalpha(stuff)), or is that only PHP or something?

Sure, you can use isdigit(...), however that doesn't really handle negative numbers properly. There are regular expression libraries, but these are cumbersome.

so:

Code:

/* returns non-zero if true */
int isAsciiInteger(char *nzstr)
{
   int dummy;
   return(sscanf(nzstr, "%d", &dummy) == 1);
}

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