Safe conversion from FString to float?

Development Programming & Scripting
1

Is there a safe way to convert from an FString of unknown content to a float (or int)? The wiki states on this page that I should use FCString::Atof(), but ideally I would like to check that the string is reasonable to convert prior to calling this and handle poor input as needed.

For example, if an input string is “foo” it is not safe to call FCString::Atof().

1 Like
2

what about checking if there are only numbers in it?

3

Hehe, fair enough. I was more looking for a pre-written function if there was one so that I could avoid writing unnecessary code. The function exists so I’ve answered and marked it as correct.

4

Clearly, I did not read the docs carefully. The function I was looking for was FString::IsNumeric().

5

I recommend FDefaultValueHelper::ParseFloat if you need the string to have decimals. IsNumeric() would return false with “12.12” because of the ‘.’ while ParseFloat recognises it’s a float.

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6

The isNumeric function is like this in the engine:

	static bool IsNumeric(const CharType* Str)
	{
		if (*Str == '-' || *Str == '+')
		{
			Str++;
		}

		bool bHasDot = false;
		while (*Str != '\0')
		{
			if (*Str == '.')
			{
				if (bHasDot)
				{
					return false;
				}
				bHasDot = true;
			}
			else if (!FChar::IsDigit(*Str))
			{
				return false;
			}
			
			++Str;
		}

		return true;
	}

“12.12” should still be considered as numeric as long as there is only one decimal point.