convert a float to string in F#?

Question

How do I convert a float to a string in F#. I'm looking for a function with this signature:

float -> string

Solution 1

> sprintf "%f";;
val it : (float -> string) = <fun:it@8>

Solution 2

As others pointed out, there are a few options. The two simplest are calling ToString method and using string function. There is a subtle difference between the two that you should be aware of. Here is what they do on my system:

> sprintf "%f" 1.2;;
val it : string = "1.200000"
> string 1.2;;
val it : string = "1.2"
> 1.2.ToString();;
val it : string = "1,2"

The first two are different, but both make sense, but why the heck did the last one return "1,2"?

That's because I have Czech regional settings where decimal point is written as comma (doh!) So, the string function uses invariant culture while ToString uses current culture (of a thread). In some weird cultures (like Czech :-)) this can cause troubles! You can also specify this explicitly with the ToString method:

> 1.2.ToString(System.Globalization.CultureInfo.InvariantCulture);;
val it : string = "1.2"

So, the choice of the method will probably depend on how you want to use the string - for presentation, you should respect the OS setting, but for generating portable files, you probably want invariant culture.

Solution 3

Use the 'string' function.

string 6.3f

Solution 4

string;;
val it : (obj -> string) = <fun:it@1>

Solution 5

Just to round out the answers:

(fun (x:float) -> x.ToString())

:)

View more solutions

Comments

[Tomas Petricek]

It really depends on how you want the resulting string to look. It may be more subtle than you think :-)

[gradbot]

This was fun answering just to see how fast others would post and up vote.

[Boti]

Might as well add in System.Convert.ToString if you're trying to round out the answers ;)

[elmattic]

Additionally you have an equivalent conversion function for other basic types with functions int, uint32, float32, byte, char, decimal, etc.

[Stephen Swensen]

The signature is deceptive here, since string is an inline statically optimized function and, when used with float, translates into something like let x = 3.2 in (# "" x : float #).ToString("g",System.Globalization.CultureInfo.InvariantCu‌​lture). Constraining the signature like (string:float->string) is a better illustration I think.

[gradbot]

I agree. MSDN also list it as the casting operator. msdn.microsoft.com/en-us/library/dd233220.aspx I'd imagine most people would want to use sprintf "%f" so you can format the float how you want.

[Tomas Petricek]

@gradbot: It was answered fast, but all answers ignored subtle aspects of fun cultures :-)!

[elmattic]

Good point, I have "1,2" too :). Fun fact: the weird cultures almost stalled developement of ALGOL according to wikipedia.

[Ramy]

couldn't select the answer for 11 minutes for some reason. So...I forgot about it for about a day.

[Friedrich Gretz]

There is another difference between the string function and the ToString method. Try applying them to null and None. While string always returns an empty string, the ToString method crashes.