C++ help, please? (fwd)

C++ help, please? (fwd)

[H.J. Lu]

Hi,

I got this. Is this an egcs bug or is the code bogus?

Thanks.

H.J.
---
I'm having a weird trouble with egcs-1.1.1 using STL stuff.
It may well be that I'm doing something wrong -  but maybe
you can spot it, as I can't. I spent the whole last night
trying to figure out what the f*** is wrong with the code
I've written - to no avail. If you could shed ANY light
on my problem(s), I'd he happy!  Thank you!

Here's the code:

#include <hash_map>

typedef const unsigned char ByteKeyID[8];

struct kcmp {
  bool operator() (ByteKeyID a, ByteKeyID b) const {
    return (memcmp(a, b, 8) == 0);
  }
};

typedef hash_map<ByteKeyID, 
  int, 
  hash<ByteKeyID>, 
  kcmp> 
hmap;

int main(int argc, char **argv)
{
  int i=0;
  ByteKeyID kid;
  hmap hm;

  for (i = 0; i < 8; i++) kid[i] = 8-i;
  hm.insert(kid, 2);

  for (i = 0; i < 8; i++) kid[i] = i;
  hm.insert(kid, 10);

  for (i = 0; i < 8; i++) kid[i] = 8-i;

  cout << "Extracted first value: ";
  cout << hm[kid] << endl;
}

Here's what the compiler says:

uri@alisan:/usr2/src/crypto-3.0 > g++ -I. -g -o v2-t v2-t.cc
/usr/include/g++-2/stl_hash_map.h: In instantiation of `hash_map<const unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<unsigned char[8], int, hash<const unsigned char[8]>, kcmp, alloc>()':
v2-t.cc:21:   instantiated from here
/usr/include/g++-2/stl_hash_map.h:78: new declaration `hash_map<unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<>()'
/usr/include/g++-2/stl_hash_map.h:78: ambiguates old declaration `hash_map<const unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<unsigned char[8], int, hash<const unsigned char[8]>, kcmp, alloc>()'
/usr/include/g++-2/stl_hash_map.h: In method `hash_map<const unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<unsigned char[8], int, hash<const unsigned char[8]>, kcmp, alloc>()':
/usr/include/g++-2/stl_hash_map.h:78: confused by earlier errors, bailing out
uri@alisan:/usr2/src/crypto-3.0 > g++ -v
Reading specs from /usr/lib/gcc-lib/i586-pc-linux-gnulibc1/egcs-2.91.60.1/specs
gcc version egcs-2.91.60.1 19990115/Linux (egcs-1.1.1 release)
uri@alisan:/usr2/src/crypto-3.0 > 

Re: C++ help, please? (fwd)

[Paul Derbyshire]

At 07:40 AM 2/16/99 -0800, H.J. Lu wrote:
>Hi,
>
>I got this. Is this an egcs bug or is the code bogus?

[deletia]

That's damned strange. The problem *appears* to be being caused by 'const'
modifiers mysteriously disappearing from your typedef'd array in the
default constructor's *template* arguments.

I'd guess it's an EGCS bug.

-- 
   .*.  "Clouds are not spheres, mountains are not cones, coastlines are not
-()  <  circles, and bark is not smooth, nor does lightning travel in a
   `*'  straight line."    -------------------------------------------------
        -- B. Mandelbrot  | http://surf.to/pgd.net
_____________________ ____|________     Paul Derbyshire     pderbysh@usa.net
Programmer & Humanist|ICQ: 10423848|

Re: C++ help, please? (fwd)

[Joe Buck]

> I got this. Is this an egcs bug or is the code bogus?

In the future please ask people to use gnu.g++.help for these.

The code is extremely bogus, however egcs-1.1.1 gets messed up by it.
The current snapshot compiler gives much better diagnostics, so it
doesn't look like we have remaining bugs.

Bogosities in the code:

1. attempt to write to a const object: note

   typedef const unsigned char ByteKeyID[8];

   the user then writes
	ByteKeyID kid;
   and proceeds to assign to its elements.

2. wrong interface to 'insert' function.  There is no insert(key,value)
   interface.  The user could write
	hm[key] = value;
   which is easy to write and to understand.  insert takes a pair.

3. hash<T> specializations are only provided for certain types,
   and arrays of 8 unsigned chars are not among them.  The user must
   supply a hash function.

4. The user appears to be counting on being able to pass arrays by value.
   One way to do this safely is to wrap the array in a struct:

struct ByteKeyID {
	unsigned char data[8];
};

   but it simply won't work otherwise.

> ...
> Here's the code:
> 
> #include <hash_map>
> 
> typedef const unsigned char ByteKeyID[8];
> 
> struct kcmp {
>   bool operator() (ByteKeyID a, ByteKeyID b) const {
>     return (memcmp(a, b, 8) == 0);
>   }
> };
> 
> typedef hash_map<ByteKeyID, 
>   int, 
>   hash<ByteKeyID>, 
>   kcmp> 
> hmap;
> 
> int main(int argc, char **argv)
> {
>   int i=0;
>   ByteKeyID kid;
>   hmap hm;
> 
>   for (i = 0; i < 8; i++) kid[i] = 8-i;
>   hm.insert(kid, 2);
> 
>   for (i = 0; i < 8; i++) kid[i] = i;
>   hm.insert(kid, 10);
> 
>   for (i = 0; i < 8; i++) kid[i] = 8-i;
> 
>   cout << "Extracted first value: ";
>   cout << hm[kid] << endl;
> }
> 
> Here's what the compiler says:
> 
> uri@alisan:/usr2/src/crypto-3.0 > g++ -I. -g -o v2-t v2-t.cc
> /usr/include/g++-2/stl_hash_map.h: In instantiation of `hash_map<const unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<unsigned char[8], int, hash<const unsigned char[8]>, kcmp, alloc>()':
> v2-t.cc:21:   instantiated from here
> /usr/include/g++-2/stl_hash_map.h:78: new declaration `hash_map<unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<>()'
> /usr/include/g++-2/stl_hash_map.h:78: ambiguates old declaration `hash_map<const unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<unsigned char[8], int, hash<const unsigned char[8]>, kcmp, alloc>()'
> /usr/include/g++-2/stl_hash_map.h: In method `hash_map<const unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<unsigned char[8], int, hash<const unsigned char[8]>, kcmp, alloc>()':
> /usr/include/g++-2/stl_hash_map.h:78: confused by earlier errors, bailing out
> uri@alisan:/usr2/src/crypto-3.0 > g++ -v
> Reading specs from /usr/lib/gcc-lib/i586-pc-linux-gnulibc1/egcs-2.91.60.1/specs
> gcc version egcs-2.91.60.1 19990115/Linux (egcs-1.1.1 release)
> uri@alisan:/usr2/src/crypto-3.0 > 
> 

C++ help, please? (fwd)

[H.J. Lu]

Hi,

I got this. Is this an egcs bug or is the code bogus?

Thanks.

H.J.
---
I'm having a weird trouble with egcs-1.1.1 using STL stuff.
It may well be that I'm doing something wrong -  but maybe
you can spot it, as I can't. I spent the whole last night
trying to figure out what the f*** is wrong with the code
I've written - to no avail. If you could shed ANY light
on my problem(s), I'd he happy!  Thank you!

Here's the code:

#include <hash_map>

typedef const unsigned char ByteKeyID[8];

struct kcmp {
  bool operator() (ByteKeyID a, ByteKeyID b) const {
    return (memcmp(a, b, 8) == 0);
  }
};

typedef hash_map<ByteKeyID, 
  int, 
  hash<ByteKeyID>, 
  kcmp> 
hmap;

int main(int argc, char **argv)
{
  int i=0;
  ByteKeyID kid;
  hmap hm;

  for (i = 0; i < 8; i++) kid[i] = 8-i;
  hm.insert(kid, 2);

  for (i = 0; i < 8; i++) kid[i] = i;
  hm.insert(kid, 10);

  for (i = 0; i < 8; i++) kid[i] = 8-i;

  cout << "Extracted first value: ";
  cout << hm[kid] << endl;
}

Here's what the compiler says:

uri@alisan:/usr2/src/crypto-3.0 > g++ -I. -g -o v2-t v2-t.cc
/usr/include/g++-2/stl_hash_map.h: In instantiation of `hash_map<const unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<unsigned char[8], int, hash<const unsigned char[8]>, kcmp, alloc>()':
v2-t.cc:21:   instantiated from here
/usr/include/g++-2/stl_hash_map.h:78: new declaration `hash_map<unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<>()'
/usr/include/g++-2/stl_hash_map.h:78: ambiguates old declaration `hash_map<const unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<unsigned char[8], int, hash<const unsigned char[8]>, kcmp, alloc>()'
/usr/include/g++-2/stl_hash_map.h: In method `hash_map<const unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<unsigned char[8], int, hash<const unsigned char[8]>, kcmp, alloc>()':
/usr/include/g++-2/stl_hash_map.h:78: confused by earlier errors, bailing out
uri@alisan:/usr2/src/crypto-3.0 > g++ -v
Reading specs from /usr/lib/gcc-lib/i586-pc-linux-gnulibc1/egcs-2.91.60.1/specs
gcc version egcs-2.91.60.1 19990115/Linux (egcs-1.1.1 release)
uri@alisan:/usr2/src/crypto-3.0 > 

Re: C++ help, please? (fwd)

[Paul Derbyshire]

At 07:40 AM 2/16/99 -0800, H.J. Lu wrote:
>Hi,
>
>I got this. Is this an egcs bug or is the code bogus?

[deletia]

That's damned strange. The problem *appears* to be being caused by 'const'
modifiers mysteriously disappearing from your typedef'd array in the
default constructor's *template* arguments.

I'd guess it's an EGCS bug.

-- 
   .*.  "Clouds are not spheres, mountains are not cones, coastlines are not
-()  <  circles, and bark is not smooth, nor does lightning travel in a
   `*'  straight line."    -------------------------------------------------
        -- B. Mandelbrot  | http://surf.to/pgd.net
_____________________ ____|________     Paul Derbyshire     pderbysh@usa.net
Programmer & Humanist|ICQ: 10423848|

Re: C++ help, please? (fwd)

[Joe Buck]

> I got this. Is this an egcs bug or is the code bogus?

In the future please ask people to use gnu.g++.help for these.

The code is extremely bogus, however egcs-1.1.1 gets messed up by it.
The current snapshot compiler gives much better diagnostics, so it
doesn't look like we have remaining bugs.

Bogosities in the code:

1. attempt to write to a const object: note

   typedef const unsigned char ByteKeyID[8];

   the user then writes
	ByteKeyID kid;
   and proceeds to assign to its elements.

2. wrong interface to 'insert' function.  There is no insert(key,value)
   interface.  The user could write
	hm[key] = value;
   which is easy to write and to understand.  insert takes a pair.

3. hash<T> specializations are only provided for certain types,
   and arrays of 8 unsigned chars are not among them.  The user must
   supply a hash function.

4. The user appears to be counting on being able to pass arrays by value.
   One way to do this safely is to wrap the array in a struct:

struct ByteKeyID {
	unsigned char data[8];
};

   but it simply won't work otherwise.

> ...
> Here's the code:
> 
> #include <hash_map>
> 
> typedef const unsigned char ByteKeyID[8];
> 
> struct kcmp {
>   bool operator() (ByteKeyID a, ByteKeyID b) const {
>     return (memcmp(a, b, 8) == 0);
>   }
> };
> 
> typedef hash_map<ByteKeyID, 
>   int, 
>   hash<ByteKeyID>, 
>   kcmp> 
> hmap;
> 
> int main(int argc, char **argv)
> {
>   int i=0;
>   ByteKeyID kid;
>   hmap hm;
> 
>   for (i = 0; i < 8; i++) kid[i] = 8-i;
>   hm.insert(kid, 2);
> 
>   for (i = 0; i < 8; i++) kid[i] = i;
>   hm.insert(kid, 10);
> 
>   for (i = 0; i < 8; i++) kid[i] = 8-i;
> 
>   cout << "Extracted first value: ";
>   cout << hm[kid] << endl;
> }
> 
> Here's what the compiler says:
> 
> uri@alisan:/usr2/src/crypto-3.0 > g++ -I. -g -o v2-t v2-t.cc
> /usr/include/g++-2/stl_hash_map.h: In instantiation of `hash_map<const unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<unsigned char[8], int, hash<const unsigned char[8]>, kcmp, alloc>()':
> v2-t.cc:21:   instantiated from here
> /usr/include/g++-2/stl_hash_map.h:78: new declaration `hash_map<unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<>()'
> /usr/include/g++-2/stl_hash_map.h:78: ambiguates old declaration `hash_map<const unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<unsigned char[8], int, hash<const unsigned char[8]>, kcmp, alloc>()'
> /usr/include/g++-2/stl_hash_map.h: In method `hash_map<const unsigned char[8],int,hash<const unsigned char[8]>,kcmp,__default_alloc_template<false,0> >::hash_map<unsigned char[8], int, hash<const unsigned char[8]>, kcmp, alloc>()':
> /usr/include/g++-2/stl_hash_map.h:78: confused by earlier errors, bailing out
> uri@alisan:/usr2/src/crypto-3.0 > g++ -v
> Reading specs from /usr/lib/gcc-lib/i586-pc-linux-gnulibc1/egcs-2.91.60.1/specs
> gcc version egcs-2.91.60.1 19990115/Linux (egcs-1.1.1 release)
> uri@alisan:/usr2/src/crypto-3.0 > 
>