Re: Check for valid number

Posted by webmaster Guido on March 18, 2001 at 20:02:20:

In Reply to: Check for valid number posted by Amit Kr Shaha on March 16, 2001 at 02:33:55:

: What is the function to check whether a text box contains a valid number or not(float,integer) ?
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You can do this with the procedure Val(S, V, Code). Example:

Function IsValidReal(S: string): Boolean;
var
V: real; // result of conversion
Code: integer; // position of first invalid character
begin
Val(S, V, Code);
Result := (Code = 0);
end;

Another example:
Function IsValidInteger(S: string): Boolean;
var
V: integer; // result of conversion
Code: integer; // position of first invalid character
begin
Val(S, V, Code);
Result := (Code = 0); // TRUE if no error
end;

Example of using this:
if IsValidReal(Edit1.Text) then ...

But be careful, this only works if the decimal separator is a POINT, meaning: 3,1415 is flagged as invalid! (Americans think everybody uses a decimal *point*, they never heard of decimal *comma*).

If your application will be used on systems with decimal point as well as systems with a decimal comma, for "real" numbers you have to do some conversions: replace the comma with a point before checking for validity. Or use a different approach with TRY... EXCEPT... and StrToFloat() -- I think that StrToFloat looks at Windows' decimal seperator.
For more info on decimal points and comma's, have a look at our Delphi Tutorial "EuroConvertor" :)