CODEWITHSUNDEEP
delphifreepascalturbo-pascal
user10051503
user10051503

Reputation:

System.Val: String to integer conversion without unambiguous base specification

I don’t understand how xa can be converted to 10 in Borland Pascal. I just use

Val('xa', value, return);

and value becomes 10, and return becomes 0 (meaning successful conversion). I’m just a newbie, can anyone explain this? I know this won’t like the ASCII cause that is just a character.

And I’m using Free Pascal ☺

I tested it in Free Pascal using xa, 0xa and $xa. So, I think Val understands the special characters like $ or 0 without me needing to call specialized functions like Hex2Dec. Is that right?

Upvotes: 0

Views: 2267

Answers (2)

Marco van de Voort
Marco van de Voort

Reputation: 26356

Since early Delphi's, the core integer conversion routines don't do just number sequences, but also some specials like Pascal "$924" for hex or C style 0x02).

FreePascal adopted it when it later started adding Delphi compatibility (roughly 1997-2003). Beside this difference, another different is that the last parameter (RETURN in your example) changed from WORD (in Turbo Pascal) to integer/longint in Delphi.

IOW, the routine accepts the x and thinks you mean to convert a C style hex number, and then interprets the "a" according to Stuart's table.

It also interprets % as binary, and & as octal.

Try

val('$10',value,return);
writeln(value,' ' ,return);  // 16 0
val('&10',value,return);
writeln(value,' ' ,return);  // 8 0
val('%10',value,return);
writeln(value,' ' ,return);  // 2 0

and compare the results.

Note that this probably won't work for very old Pascal's like Turbo Pascal, and Free Pascals from before the year 2000. The % and & are FPC specific to match the literal notation extensions (analogous to $, but for binary and octal)

var x : Integer
begin
x:=%101010;  //42
x:=&101;     //65

Upvotes: 6

Stuart
Stuart

Reputation: 1438

This won't work with all Pascal compilers, and you didn't say what Pascal compiler you are using, but it looks like, the x in 'xa' says that this is a hexadecimal (base 16) number, and the value of the digits in a hexadecimal number are as follows:

Digit Value
0      0
1      1
2      2
3      3
4      4
5      5
6      6
7      7
8      8
9      9
a     10
A     10
b     11
B     11
c     12
C     12
d     13
D     13
e     14
E     14
f     15
F     15

Upvotes: 2

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