atof conversion error

codeman · 07-03-2009, 06:01 PM

I realize this is probably a stupid question, I just don't use these routines much and thus am ... well, ignorant.

I call atof with a string of "18.69".

The result is 18.690000534.

Why ? Do I have to come up with a wrapper function if I am always working with figures out to two decimal places and want just that - just 18.69 ?

Adak · 07-03-2009, 06:22 PM

You can specify that the answer be printed out only to the first 2 decimal places:

Code:

dbl_number = 17.123456;
printf("dbl_number to two decimal places is: %.2f \n", dbl_number);

codeman · 07-03-2009, 06:39 PM

Foolish me.

I'm assuming the conversion might be ok. It's just my IDE telling me the value is 18.690000534.

I assign 18.69 to a float value, then break, and place the mouse cursor over the value. The IDE (Borland C++ Builder version 5.0 Prodfessional) says it's 18.690000534.

tabstop · 07-03-2009, 11:10 PM

Quote:

Originally Posted by codeman

Foolish me.

I'm assuming the conversion might be ok. It's just my IDE telling me the value is 18.690000534.

I assign 18.69 to a float value, then break, and place the mouse cursor over the value. The IDE (Borland C++ Builder version 5.0 Prodfessional) says it's 18.690000534.

Very possible. It's highly unlikely the value of a float variable can ever actually be 18.69 exactly (it's certainly impossible if your machine follows the IEEE standard).

07-03-2009, 06:01 PM	#1
codeman Registered User Join Date: Jul 2009 Posts: 2	atof conversion error I realize this is probably a stupid question, I just don't use these routines much and thus am ... well, ignorant. I call atof with a string of "18.69". The result is 18.690000534. Why ? Do I have to come up with a wrapper function if I am always working with figures out to two decimal places and want just that - just 18.69 ?
codeman is offline

07-03-2009, 06:22 PM	#2
Adak Registered User Join Date: Sep 2006 Posts: 2,501	You can specify that the answer be printed out only to the first 2 decimal places: Code: dbl_number = 17.123456; printf("dbl_number to two decimal places is: %.2f \n", dbl_number);
Adak is offline

07-03-2009, 06:39 PM	#3
codeman Registered User Join Date: Jul 2009 Posts: 2	correction Foolish me. I'm assuming the conversion might be ok. It's just my IDE telling me the value is 18.690000534. I assign 18.69 to a float value, then break, and place the mouse cursor over the value. The IDE (Borland C++ Builder version 5.0 Prodfessional) says it's 18.690000534.
codeman is offline

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