Setlength problem

[acp693]

Can anyone help me understand what I'm doing wrong here?  Thank you!

Code: Pascal  [Select][+][-]

1.  
2. setlength(somearray, someinteger); // this works
3. setlength(anotherarray, trunc((someinteger-1)/2) ); // this doesn't work Error Type mismatch.
4.  

[440bx]

I haven't tried what I'm going to suggest but, I believe that if you change the numeral 1 to 1.0 or the numeral 2 to 2.0 (in the second call to setlength), you should no longer get a type mismatch.

[Handoko]

Tested on Lazarus 2.0.10, this works:

Code: Pascal  [Select][+][-]

1. procedure TForm1.Button1Click(Sender: TObject);
2. Type
3.   TMyArray = array of Byte;
4. var
5.   SomeArray, AnotherArray: TMyArray;
6.   SomeInteger: Integer;
7. begin
8.   SomeInteger := 10;
9.   SetLength(SomeArray, SomeInteger);
10.   SetLength(AnotherArray, Trunc((SomeInteger-1)/2));
11. end;

No compile time nor runtime error, just some hints.

[acp693]

Thanks, I've just tried that, but still the same error.

[acp693]

Tested on Lazarus 2.0.10, this works:

Code: Pascal  [Select][+][-]

1. procedure TForm1.Button1Click(Sender: TObject);
2. Type
3.   TMyArray = array of Byte;
4. var
5.   SomeArray, AnotherArray: TMyArray;
6.   SomeInteger: Integer;
7. begin
8.   SomeInteger := 10;
9.   SetLength(SomeArray, SomeInteger);
10.   SetLength(AnotherArray, Trunc((SomeInteger-1)/2));
11. end;

No compile time nor runtime error, just some hints.

Oh, I don't see any appreciable differences between your code and mine...

[Handoko]

That's why it's usually good to show us the whole source code. Only 2 lines did not say anything useful.

Most inexperienced programmers usually think the problem is on a certain spot but actually it is elsewhere.

[egsuh]

I think it should work as Handoko said, but the definition on the document says they are defined as follows in system unit (and maybe others as well).

Code: Pascal  [Select][+][-]

1. type Longint = - 2147483648..2147483647;
2. type SizeInt = LongInt;
3. type Int64 = - 9223372036854775808..9223372036854775807;
4.  
5. function Trunc(d: ValReal):Int64;
6. procedure SetLength(var A: DynArrayType;  Len: SizeInt);

So the type mismatch may be between LongInt and Int64.

[440bx]

So the type mismatch may be between LongInt and Int64.

I don't know FPC internals well enough to affirmatively state the reason why FPC issues a type mismatch but, the second expression is using a real operator (the "/") to divide two integers and, that is in strict terms incorrect.  The "/" applies only to real types, it is for that reason that I suggested you change either the 1 to 1.0 or the 2 to 2.0.  That should cause the compiler to promote the integer types to reals causing the "/" operator to then be correct.  IOW, using "/" to divide integers isn't correct, integer division should be carried out with "div" not "/".

[Handoko]

No need to guess, without seeing more lines of the source we won't know what is the culprit.

But guessing is fun.
My guess: that array is a fix size array.

I don't have a magic ball but I have magic eyes. 

[bytebites]

So the type mismatch may be between LongInt and Int64.

I don't know FPC internals well enough to affirmatively state the reason why FPC issues a type mismatch but, the second expression is using a real operator (the "/") to divide two integers and, that is in strict terms incorrect.  The "/" applies only to real types, it is for that reason that I suggested you change either the 1 to 1.0 or the 2 to 2.0.  That should cause the compiler to promote the integer types to reals causing the "/" operator to then be correct.  IOW, using "/" to divide integers isn't correct, integer division should be carried out with "div" not "/".

Your explanation may apply to C-derived languages but not Pascal. In Pascal operands of /-division can be integers.

[Thaddy]

Code: Pascal  [Select][+][-]

1. (SomeInteger-1) div 2;

Does not need trunc.

[PascalDragon]

Can anyone help me understand what I'm doing wrong here?  Thank you!

As others already wrote, please provide a full example.

So the type mismatch may be between LongInt and Int64.

I don't know FPC internals well enough to affirmatively state the reason why FPC issues a type mismatch but, the second expression is using a real operator (the "/") to divide two integers and, that is in strict terms incorrect.  The "/" applies only to real types, it is for that reason that I suggested you change either the 1 to 1.0 or the 2 to 2.0.  That should cause the compiler to promote the integer types to reals causing the "/" operator to then be correct.  IOW, using "/" to divide integers isn't correct, integer division should be carried out with "div" not "/".

FPC's /-operator takes both floating point and integer types. However it always results in a floating point type.

Code: Pascal  [Select][+][-]

1. (SomeInteger-1) div 2;

Does not need trunc.

That would indeed be the cleanest solution, though I'd still be interested in the full code that fails just to make sure that this isn't a bug in the compiler...

[440bx]

Your explanation may apply to C-derived languages but not Pascal.

You may be right about that but, I am not sure.  I'd have to review what the Pascal standard says.

In Pascal operands of /-division can be integers.

_IF_ that is true then it introduces an inconsistency in the language because real_type div real_type is not allowed while, if what you are stating is correct, integer_type / integer_type is allowed.  That would be an undesirable inconsistency.

@OP,

Did you try my suggestion and, if so, did it eliminate the type mismatch message ?

ETA

FPC's /-operator takes both floating point and integer types. However it always results in a floating point type.

Thank you for the clarification.

[PascalDragon]

In Pascal operands of /-division can be integers.

_IF_ that is true then it introduces an inconsistency in the language because real_type div real_type is not allowed while, if what you are stating is correct, integer_type / integer_type is allowed.  That would be an undesirable inconsistency.

ISO Pascal 6.7.2.1, table 3: the division operator takes both real_type and integer_type as operands.

[440bx]

ISO Pascal 6.7.2.1, table 3: the division operator takes both real_type and integer_type as operands.

Thank you.