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Casting literals causes trouble
#416916
02/05/13 21:33
02/05/13 21:33
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Joined: Jan 2002
Posts: 4,225
Germany / Essen
Uhrwerk
OP
Expert
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OP
Expert
Joined: Jan 2002
Posts: 4,225
Germany / Essen
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This one really knocked my socks off. 
#include <acknex.h>
int x = (int)1;
void main()
{
printf("%d",x);
}
I still have a feeling I overlooked something...
Always learn from history, to be sure you make the same mistakes again...
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Re: Casting literals causes trouble
[Re: jcl]
#416952
02/06/13 13:35
02/06/13 13:35
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Joined: Jan 2002
Posts: 4,225
Germany / Essen
Uhrwerk
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Posts: 4,225
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Fixing the code isn't a problem as the cast is pointless and simply can be omitted. It also works when defining x as a local variable. But that does not help me get my socks back on...  I'm curious where the syntax error hides...
Always learn from history, to be sure you make the same mistakes again...
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Re: Casting literals causes trouble
[Re: Uhrwerk]
#416958
02/06/13 14:08
02/06/13 14:08
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Joined: Mar 2011
Posts: 3,150
Budapest
sivan
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Joined: Mar 2011
Posts: 3,150
Budapest
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-
Last edited by sivan; 02/06/13 14:08.
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Re: Casting literals causes trouble
[Re: sivan]
#417007
02/07/13 09:31
02/07/13 09:31
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Joined: Jul 2000
Posts: 27,986
Frankfurt
jcl
Chief Engineer
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Chief Engineer
Joined: Jul 2000
Posts: 27,986
Frankfurt
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Ok, here's the solution: In a programming language, all expressions must be inside functions. Outside a function you can initialize a variable with a constant, but not with an expression. The reason is that the result of an expression is normally not known at compile time, but only at runtime. In lite-C an expression is any value that is not a constant. int x = 1; // ok int x = y; // not ok int x = sqrt(1); // not ok int x = (int)1; // not ok I hope you see now why your code can not work. Here's the fixed version:
#include <acknex.h>
int x;
void main()
{
x = (int)1;
printf("%d",x);
}
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Re: Casting literals causes trouble
[Re: jcl]
#417014
02/07/13 10:33
02/07/13 10:33
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Joined: Dec 2008
Posts: 1,218
Germany
Rackscha
Serious User
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Serious User
Joined: Dec 2008
Posts: 1,218
Germany
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@JCL: Constant expressions can be evaluated in programminglanguages (and thats what (int)1 is) And maybe its possible to add an error message if a dynamic expression is used for initialization? It does not work, so the compiler should abort(or am i wrong?)
Last edited by Rackscha; 02/07/13 10:33.
MY Website with news of my projects: (for example my current Muliplayer Bomberman, GenesisPrecompiler for LiteC and TileMaster, an easy to use Tile editor) Sparetime-Development
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Re: Casting literals causes trouble
[Re: jcl]
#417048
02/07/13 18:33
02/07/13 18:33
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Joined: Jan 2002
Posts: 4,225
Germany / Essen
Uhrwerk
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Posts: 4,225
Germany / Essen
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In a programming language, all expressions must be inside functions. That's not true. Neither for programming languages in general, nor for Lite-C. The c standard includes constant expressions for very good reason. And you obviously followed the standard at very least partially:
#include <acknex.h>
int my_flag = PASSABLE;
void main()
{
printf("%d",my_flag);
}
You can also replace "PASSABLE" by "(1 << 9)", hence the expression evaluation cannot be done by the precompiler. It already has to be implemented in the compiler. You can even do more complex expressions, like "2 + 2 * 2 % 2". I did some quick tests and the results suggest that you already implemented correct operator precedence for static expressions. I'd love to see this functionality expanded to fully meet the c standard. @Rakscha This is also a bug, as the compiler should give a syntax error here.
Always learn from history, to be sure you make the same mistakes again...
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