Tricky Situation: Atof function converting strings to inf or nan

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This blog post says about a tricky situation when using atof function. The atof function converts a string argument to a floating point number.

If the string to be converted starts with "inf" or "nan", the atof function converts the string to inf/nan instead of converting to 0.
inf represents "Positive Infinity" and nan represents a value which is "Not a Number".

For eg: The following strings will convert to inf when using atof function.
  • Information -> inf
  • Infection -> inf
  • Influenza -> inf
  • etc...
The following strings will convert to nan when using atof function.
  • Nanotechnology -> nan
  • Nanogram -> nan
  • etc...
This issue can cause downstream impacts if you are using the converted values to be saved to database or other application.

The following C++ program shows the above issue:


















This issue can be corrected by using a simple which checks if the string starts with inf and if so, it can be programmed to prevent from passing to atof function and parse 0 instead.

The function looks like the below:


if (((word[0] == 'i') || (word[0] == 'I')) && ((word[1] == 'n') || (word[1] == 'N')) && ((word[2] == 'f') || (word[2] == 'F')))
 {
  value1 = 0;
 }
 else
 {
  value1 = atof(word);
 }

On debugging, we can see that correct value of 0 is passed (as shown below)


Similar Posts:

1) Anonymous classes in C++
2) Program to check whether a system is big-endian or little-endian

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