[fpc-pascal] Something like "Is a number"?

A.J. Venter ajventer at direq.org
Sat Jul 9 11:59:51 CEST 2005

> >You can use val(str, int/real, err)
> >
> >if err is 0, the string was converted to an integer or real (depending on
> >the type of int/real.
> >
> >John
> Thank you, it's working!!!
Yes that's the old Pascal version of StrToInt :) and it had errorchecking :)
Just for the record, like everything it has more than one answer, you could 
also have done:
 Int := strToInt(Str);
 Int := -1 {Or whatever error number}

Or if you wanted to prepend exceptions rather than catch them, the following
function could also work have worked (note you have to do a shortString cast, 
AnsiStrings don't like access by character)

Function IsANumber (InStr : String) : Boolean
Var TempBool : Boolean;
      Str : ShortString;
      I : Integer;
Str := ShortString(InStr);
TempBool := True;
I := 1;

While (I <= Length(Str)) and (TempBool = True) do
 TempBool := Str[I] in ['0'..'9'];

IsANumber := TempBool

Of course, that's a rather ugly way to do it, I don't suggest it in practice 
except for very special cases but I put it here to give an idea of the ways 
you can interact between types. One of Pascal's (and by inheritance object 
pascal's) greatest features is that it is not only strongly typed but has 
very strict type checking, which prevents a very large number of the problems 
C coders face. For starters you don't have to take measures against about a 
potential buffer overflow every time you use strings, it does mean though 
that getting data from one type to another is sometimes a little harder than 
a simple cast (like in say java), but if you understand the ways in which 
data types are actually implemented and how they relate to each other you can 
do not only everything you can do in untyped or weakly-typed languages but a 
great deal more.


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