GCC compile problem ...

GCC compile problem ...

[gcc]

Hello!

I have the following compile problem with gcc 3.0.4.

Borland C++ 5.5 and Microsoft Visual C++ 6.0 works well.

#include <string>
#include <iostream>

using namespace std;

class Test
{
public:
        string getString() { return "hallo"; }
};

int main(int argc, char* argv)
{
        Test test;

        string& s = test.getString(); // Error here
        // works well: string s = test.getString();
        cout << s << "\n";

        // gcc --version: 3.0.4
}

main.cpp: In function `int main (int, char *)':
main.cpp:17: initialization of non-const reference type `class string
&'
main.cpp:17: from rvalue of type `basic_string<char,
string_char_traits<char>, __default_alloc_template<true, 0> >'
make[1]: *** [main.o] Error 1

Why aren't there references allowed here with gcc? Is this not Ansi C++
conform?

Ciao,
Gerhard

Re: GCC compile problem ...

[Sebastian Huber]

Hi!

On Friday 27 September 2002 09:09, gcc@wiesinger.com wrote:
> Hello!
>
> I have the following compile problem with gcc 3.0.4.
>
> Borland C++ 5.5 and Microsoft Visual C++ 6.0 works well.
>
> #include <string>
> #include <iostream>
>
> using namespace std;
>
> class Test
> {
> public:
>         string getString() { return "hallo"; }
> };
>
> int main(int argc, char* argv)
> {
>         Test test;
>
>         string& s = test.getString(); // Error here

This is not ok, because you try to initialize a non-const reference with a 
temporary string object.

>         // works well: string s = test.getString();

This is ok, because of the assignment operator looks like:
operator=( const std::string&)

>         cout << s << "\n";

This is also ok, because the overloaded shift operator takes a constant 
reference.

>         // gcc --version: 3.0.4
> }
>
> main.cpp: In function `int main (int, char *)':
> main.cpp:17: initialization of non-const reference type `class string
> &'
> main.cpp:17: from rvalue of type `basic_string<char,
> string_char_traits<char>, __default_alloc_template<true, 0> >'
> make[1]: *** [main.o] Error 1
>
> Why aren't there references allowed here with gcc? Is this not Ansi C++
> conform?
>
> Ciao,
> Gerhard

Re: GCC compile problem ...

[John Love-Jensen]

Hi Gerhard,

The TEMPORARY from test.getString is being set to a REFERENCE.

The TEMPORARY is destructed, more-or-less, after the semicolon that set the
string reference to the temporary.

The cout << s << "\n"; is operating on the s string that has been
destructed, which is very dangerous.  Who knows what state that freed STACK
memory and HEAP memory will be in, especially during the machinations of the
ostream processing.

Borland C++ 5.5 and Microsoft Visual C++ 6.0 should be ashamed.  Shame.
Shame.

--Eljay

Re: GCC compile problem ...

[Sebastian Huber]

Hello John,

On Friday 27 September 2002 09:31, John Love-Jensen wrote:
> Hi Gerhard,
>
> The TEMPORARY from test.getString is being set to a REFERENCE.
>
> The TEMPORARY is destructed, more-or-less, after the semicolon that set the
> string reference to the temporary.
>
> The cout << s << "\n"; is operating on the s string that has been
> destructed, which is very dangerous.

I think, that this is not true. If you assign a temporary object to a constant 
reference, the object will survive until the reference is destroyed.

> Who knows what state that freed STACK
> memory and HEAP memory will be in, especially during the machinations of
> the ostream processing.
>
> Borland C++ 5.5 and Microsoft Visual C++ 6.0 should be ashamed.  Shame.
> Shame.
>
> --Eljay

Bye

Re: GCC compile problem ...

[John Love-Jensen]

Hi Sebastian,

> I think, that this is not true. If you assign a temporary object to a constant
> reference, the object will survive until the reference is destroyed.

Thanks Sebastian, I stand corrected!  A const-reference has lifespan beyond
the full expression.

q.v. Stroustrup's C++PL 3rd ed, section 10.4.10

Sincerely,
--Eljay

Live like you'll die tomorrow.  Learn like you'll live forever.

gcc compile problem ...

[Brian J. Dent]

gcc help,

Obviously I am new to the GNU gcc compiler.

I've been trying compile a program on our SUN with gcc 
(sparc-sun-solaris2.7/2.95.1) and it contains some intrinsic 
functions.  When I get to the point of linking it doesn't recognize the 
functions, eg:  sqrt.  Below is a test program.  What is missing that I am 
not finding the built-in functions to link with?  Thanks for any help.

file:marc.c:
#include <stdio.h>
#include <math.h>

main()
{
         double x = 2;
         printf("sqrt of %d is %f\n",x,sqrt(x));
}

gcc -c marc.c
gcc -o marc.out marc.o
Undefined                       first referenced
  symbol                             in file
sqrt                                marc.o
ld: fatal: Symbol referencing errors. No output written to marc.out
collect2: ld returned 1 exit status

- bjd
____________________________
Brian J. Dent
CompuDent
v (831) 649-0948 f (707) 222-1209
http://www.redshift.com/~briandent/

Re: gcc compile problem ...

[Alexandre Oliva]

On Jan 26, 2000, "Brian J. Dent" <briandent@redshift.com> wrote:

> sqrt                                marc.o
> ld: fatal: Symbol referencing errors. No output written to marc.out

Try `-lm'.  Math functions are defined in libm.

-- 
Alexandre Oliva http://www.ic.unicamp.br/~oliva IC-Unicamp, Bra[sz]il
oliva@{lsd.ic.unicamp.br,guarana.{org,com}} aoliva@{acm,computer}.org
oliva@{gnu.org,kaffe.org,{egcs,sourceware}.cygnus.com,samba.org}
** I may forward mail about projects to mailing lists; please use them

Re: gcc compile problem ...

[Alexandre Oliva]

On Jan 26, 2000, "Brian J. Dent" <briandent@redshift.com> wrote:

> sqrt                                marc.o
> ld: fatal: Symbol referencing errors. No output written to marc.out

Try `-lm'.  Math functions are defined in libm.

-- 
Alexandre Oliva http://www.ic.unicamp.br/~oliva IC-Unicamp, Bra[sz]il
oliva@{lsd.ic.unicamp.br,guarana.{org,com}} aoliva@{acm,computer}.org
oliva@{gnu.org,kaffe.org,{egcs,sourceware}.cygnus.com,samba.org}
** I may forward mail about projects to mailing lists; please use them

gcc compile problem ...

[Brian J. Dent]

gcc help,

Obviously I am new to the GNU gcc compiler.

I've been trying compile a program on our SUN with gcc 
(sparc-sun-solaris2.7/2.95.1) and it contains some intrinsic 
functions.  When I get to the point of linking it doesn't recognize the 
functions, eg:  sqrt.  Below is a test program.  What is missing that I am 
not finding the built-in functions to link with?  Thanks for any help.

file:marc.c:
#include <stdio.h>
#include <math.h>

main()
{
         double x = 2;
         printf("sqrt of %d is %f\n",x,sqrt(x));
}

gcc -c marc.c
gcc -o marc.out marc.o
Undefined                       first referenced
  symbol                             in file
sqrt                                marc.o
ld: fatal: Symbol referencing errors. No output written to marc.out
collect2: ld returned 1 exit status

- bjd
____________________________
Brian J. Dent
CompuDent
v (831) 649-0948 f (707) 222-1209
http://www.redshift.com/~briandent/