Re: %union errors

[Luca]

Laurence Finston ha scritto:
> On Fri, 5 Dec 2008, Benny Hardage wrote:
>
>   
> > %union
> > {
> >         int intVal;
> >         bool boolVal;
> >         char* strVal;
> >         std::list<const Variable::Qualifier*>* qList;
> >         Variable* var;
> >         UnaryOperation* uop;
> >         BinaryOperation* binop;
> >         Expression* expr;
> >         DataLiteral* datalit;
> > }
> >
> >     
>
> I had a problem trying to use types defined in the STL in the `%union'.  
> I don't remember the details, but I believe it involved types where the
> size isn't known at compile-time not being permitted in unions.  
I think you're wrong. The size of a pointer is always known at compile 
time,  std::list<const Variable::Qualifier*>* qList is a pointer and not 
an object. The size is 4 bytes using a 32 bit OS. Bison union is a 
standard union, you can put any type inside. For example, I can compile 
a union with vector:

%union
{
       int intVal;
       bool boolVal;
        std::vector<int>* pVectorInt;
};

You can also insert a pointer to a known class, if you need 


class MyClass;
%union
{
       int intVal;
       bool boolVal;
        MyClass* pMyClass;
};

I think the problem concern Variable::Qualifier. This type is known by the 
compiler in y.tab.c (or y.tab.cpp) because the user add the right include file 
(or add some definitions) in the first section (before the first %%) inside .y 
file. The problem arises when your using y.tab.h: here the union is reported 
without the user definitions: for example the previous union uses MyClass but 
it is an undefined symbol

//inside y.tab.h
typedef union YYSTYPE
{
       int intVal;
       bool boolVal;
        MyClass* pMyClass;              //compiler can complain about MyClass 
type!!!

} YYSTYPE;

so if you include y.tab.h inside a .c or .cpp file where MyClass isn't a 
defined type you'll have an error.



There is a simple fix, use 3 .h file:

-y.tab.h
-userdef.h
-bisondef.h

In userdef.h put all user definition, for example:
class MyClass;


in bisondef.h include put user definitions BEFORE y.tab.h
#include userdef.h
#include y.tab.h

then use biosondef.h in place of y.tab.h anywhere in your source code. 

In this way you can also redefine YYLTYPE (user custom locations), YYLLOC_DEFAULT (to merge locations) and YY_LOCATION_PRINT (to print locations) without any trouble. 

Luca

> I think 
> there was something about constructors as well.  I believe this is 
> documented in the section about unions in Stroustrup's _The C++ Programming 
> Language_.  At any rate, I couldn't get it to work.
>
> My unions for Bison usually contain an `int', a `float', a `char' vector, and
> a `void*' for everything else.  `void*' as `YYSTYPE' would do the trick, 
> but I find it convenient to have semantic values of the other types
> without having to use casts.
>
> Laurence Finston
>
> On Fri, 5 Dec 2008, Benny Hardage wrote:
>
>   
> > Hello,
> >
> > I'm receiving the following errors when I compile:
> >
> > In file included from compiler.l:17:
> > parser.y:27: error: ISO C++ forbids declaration of 'list' with no type
> > parser.y:27: error: invalid use of '::'
> > parser.y:27: error: expected ';' before '<' token
> > parser.y:28: error: ISO C++ forbids declaration of 'Variable' with no type
> > parser.y:28: error: expected ';' before '*' token
> > parser.y:29: error: ISO C++ forbids declaration of 'UnaryOperation' with no type
> > parser.y:29: error: expected ';' before '*' token
> > parser.y:30: error: ISO C++ forbids declaration of 'BinaryOperation'
> > with no type
> > parser.y:30: error: expected ';' before '*' token
> > parser.y:31: error: ISO C++ forbids declaration of 'Expression' with no type
> > parser.y:31: error: expected ';' before '*' token
> > parser.y:32: error: ISO C++ forbids declaration of 'DataLiteral' with no type
> > parser.y:32: error: expected ';' before '*' token
> >
> > I've seen a fairly old thread that attempted to address this issue,
> > saying that my include files might not be in the right order, but the
> > top of my file looks like the following:
> >
> > %error-verbose
> >
> > %{
> >
> > int yylex();
> >
> > #include <iostream>
> > #include "expressions.hpp"
> > #include "statements.hpp"
> >
> > extern bool outputTokens;
> > extern bool outputParser;
> >
> > void yyerror( char* msg )
> > {
> >         std::cerr << msg << std::endl;
> > }
> >
> > %}
> >
> > %union
> > {
> >         int intVal;
> >         bool boolVal;
> >         char* strVal;
> >         std::list<const Variable::Qualifier*>* qList;
> >         Variable* var;
> >         UnaryOperation* uop;
> >         BinaryOperation* binop;
> >         Expression* expr;
> >         DataLiteral* datalit;
> > }
> >
> > expressions.hpp contains the datatypes in question.
> >
> > I was wondering if someone might let me know what I was doing wrong.
> >
> > Thanks,
> > B.J.
> >
> >
> > _______________________________________________
> > address@hidden http://lists.gnu.org/mailman/listinfo/help-bison
> >
> >     
>
>
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