g++ 2.7.0: bool vs. string vs. const char* overloading

Thread View: gnu.g++.help

3 messages

[T] Back to Threads [V] Tree View [G] Group Articles

3 total messages Started by Per Abrahamsen Thu, 02 Nov 1995 13:45

#813

Author: Per Abrahamsen
Date: Thu, 02 Nov 1995 13:45

53 lines
2663 bytes

Can anyone explain to me why two doIt calls below select different
overloaded functions?

------------- bug.C -------------
#include <iostream.h>
#include <string>

void doIt (string)
{
  cout << "Gotta string\n";
}

void doIt (bool)
{
  cout << "Gotta bool\n";
}

int main ()
{
  const char* const cp = "Hi!";
  doIt (cp);
  doIt ("Hi!");
  return 0;
}
--------------------------------

daisy% c++ -Wall -g  -v -o bug bug.C
 gcc -Wall -g -v -o bug bug.C -lstdc++
Reading specs from /pack/gcc/lib/gcc-lib/sparc-sun-solaris2.4/2.7.0/specs
gcc version 2.7.0
 /pack/gcc/lib/gcc-lib/sparc-sun-solaris2.4/2.7.0/cpp -lang-c++ -v -undef -D__GNUC__=2 -D__GNUG__=2 -D__cplusplus -D__GNUC_MINOR__=7 -Dsun -Dsparc -Dunix -D__svr4__ -D__SVR4 -D__GCC_NEW_VARARGS__ -D__sun__ -D__sparc__ -D__unix__ -D__svr4__ -D__SVR4 -D__GCC_NEW_VARARGS__ -D__sun -D__sparc -D__unix -Asystem(unix) -Asystem(svr4) -Acpu(sparc) -Amachine(sparc) -g -Wall bug.C /var/tmp/cca000ah.ii
GNU CPP version 2.7.0 (sparc)
#include "..." search starts here:
#include <...> search starts here:
 /pack/gcc/lib/g++-include
 /usr/local/include
 /pack/gcc/sparc-sun-solaris2.4/include
 /pack/gcc/lib/gcc-lib/sparc-sun-solaris2.4/2.7.0/include
 /usr/include
End of search list.
 /pack/gcc/lib/gcc-lib/sparc-sun-solaris2.4/2.7.0/cc1plus /var/tmp/cca000ah.ii -quiet -dumpbase bug.cc -g -Wall -version -o /var/tmp/cca000ah.s
GNU C++ version 2.7.0 (sparc) compiled by GNU C version 2.7.0.
 /usr/ccs/bin/as -V -Qy -s -o /var/tmp/cca000ah1.o /var/tmp/cca000ah.s
/usr/ccs/bin/as: SC3.1 dev 09 May 1994
 /usr/ccs/bin/ld -V -Y P,/usr/ccs/lib:/usr/lib -Qy -o bug /pack/gcc/lib/gcc-lib/sparc-sun-solaris2.4/2.7.0/crt1.o /pack/gcc/lib/gcc-lib/sparc-sun-solaris2.4/2.7.0/crti.o /usr/ccs/lib/values-Xa.o /pack/gcc/lib/gcc-lib/sparc-sun-solaris2.4/2.7.0/crtbegin.o -L/pack/gcc/lib/gcc-lib/sparc-sun-solaris2.4/2.7.0 -L/usr/ccs/bin -L/usr/ccs/lib -L/pack/gcc/lib /var/tmp/cca000ah1.o -lstdc++ -lgcc -lc -lgcc /pack/gcc/lib/gcc-lib/sparc-sun-solaris2.4/2.7.0/crtend.o /pack/gcc/lib/gcc-lib/sparc-sun-solaris2.4/2.7.0/crtn.o

ld: Software Generation Utilities (SGU) SunOS/ELF (LK-1.4 (S/I))
daisy% bug
Gotta bool
Gotta string

Compilation finished at Thu Nov  2 14:37:47

Re: g++ 2.7.0: bool vs. string vs. const char* overloading

#814

Author: Alex Martelli
Date: Thu, 02 Nov 1995 22:52

28 lines
1490 bytes

abraham@dina.kvl.dk (Per Abrahamsen) writes:
	...
>Can anyone explain to me why two doIt calls below select different
>overloaded functions?
	...
>void doIt (string)
	...
>void doIt (bool)
	...
>  const char* const cp = "Hi!";
>  doIt (cp);
>  doIt ("Hi!");

There is no conversion from a const char* to a non-const string,
while there is one from any pointer to bool, so the first call
will surely end up calling doIt(bool).  The literal "Hi!" is
a (non-const) char* (for historical reasons) -- I confess I'm
not sure why the user-defined conversion to string is
unambiguously preferred to the builtin one to bool (perhaps
the latter would have to go through a _const_ char*...?)

Alex
--
DISCLAIMER: these are TOTALLY personal opinions and viewpoints, NOT connected
in any way with my employer, nor any other organization or individual!
Email: martelli@cadlab.it                            Phone: +39 (51) 597313
CAD.LAB s.p.a., v. Ronzani 7/29, Casalecchio, Italia   Fax: +39 (51) 597120

Re: g++ 2.7.0: bool vs. string vs. const char* overloading

#816

Author: James Kanze US/ESC 60/3/141 #407...
Date: Fri, 03 Nov 1995 11:00

48 lines
1857 bytes

In article <199511021344.OAA02487@ssv4.dina.kvl.dk>
abraham@dina.kvl.dk (Per Abrahamsen) writes:

|> Can anyone explain to me why two doIt calls below select different
|> overloaded functions?

Compiler bug?

|> ------------- bug.C -------------
|> #include <iostream.h>
|> #include <string>

|> void doIt (string)
|> {
|>   cout << "Gotta string\n";
|> }

|> void doIt (bool)
|> {
|>   cout << "Gotta bool\n";
|> }

|> int main ()
|> {
|>   const char* const cp = "Hi!";
|>   doIt (cp);

Should call do( bool ), since a pointer converts to a bool implicitly
(and the conversion, which doesn't use any user defined conversions,
has precedence over the conversion to string, which involves calling
the constructor).

|>   doIt ("Hi!");

Same as above.

|>   return 0;
|> }

Rigorously speaking, it is an error.  On the other hand, I can easily
imagine a compiler having an extension which allows literal string
constants (like "Hi!") to be treated exactly as strings (even up to
correctly initializing static memory for a string statically).
-- 
James Kanze         Tel.: (+33) 88 14 49 00        email: kanze@gabi-soft.fr
GABI Software, Sarl., 8 rue des Francs-Bourgeois, F-67000 Strasbourg, France
Conseils en informatique industrielle --
                              -- Beratung in industrieller Datenverarbeitung

Thread Navigation

This is a paginated view of messages in the thread with full content displayed inline.

Messages are displayed in chronological order, with the original post highlighted in green.

Use pagination controls to navigate through all messages in large threads.

Back to All Threads