string literal conversion problem

string literal conversion problem

[Jack Marr]

We are getting an error with g++ 3.3.3 when passing a string literal to 
a function expecting a void *.  The error is seen here:

% cat strlit-to-void-ptr.c

extern void setValue(void * value);

int main(void)
{
          setValue("String 1");

          char * s2 = "String 2";
          setValue(s2);

          return 0;
}

% g++ -c strlit-to-void-ptr.c
strlit-to-void-ptr.c: In function `int main()':
strlit-to-void-ptr.c:6: error: invalid conversion from `const void*' to
`void*'

It seems to me that the conversion of 'const char *' to 'char *'
specified in ISO 14882 4.2 ¶2 should be applied prior to the conversion 
of 'char *' to 'void *' spec'd in 4.10.  I believe this is what allows 
the declaration and use of s2 to compile without error.

Also, we don't get a warning for this practice with any of the other 4 
compilers we use, which doesn't prove anything but does provide some 
support.  Are all of those compilers in fact non-compliant or is this a 
g++ bug?

-- 
        Jack Marr (marr@ugs.com)
        UGS -- Development Environment Tools
        Cypress, CA  "Ite Ursi"

Re: string literal conversion problem

[Eljay Love-Jensen]

Hi Jack,

I reread ISO 14882 4.2 and 4.10.  Hmm, not sure.

The VERY VERY VERY compliant and strict Edison Design Group C++ front end 
(http://www.edg.com/cpp.html) via Comeau 
(http://www.comeaucomputing.com/tryitout/) compiler reject your code.

argument of type "const char *" is incompatible with parameter of type "void *"

I'm thinking that your code is not 100% compliant.

You could use the GCC -fno-const-strings compiler flag to work around the 
issue that you ran into to with GCC.

Or you could change...
extern void setValue(void * value);
...to...
extern void setValue(void const* value);

Sincerely,
--Eljay