Lighter wrote:
> Is overriding a function of a library in accordance with C++ standard?
>
> The following code is passed by the VS 2005 and Dev C++.
>
> #include <cstdlib>
> #include <iostream>
>
> using namespace std;
>
> size_t strlen(const char* p)
> {
>     return 0;
> } // !!! Note this !!! The standard library function strlen is
> deliberately overriden.
>
> int main(int argc, char *argv[])
> {
>
>     system("PAUSE");
>
>     return EXIT_SUCCESS;
> }
>
BTW this is not a question for comp.std.c++ (comp.lang.c++ is more
appropriate).

It is not overriding (overriding involve inheritance & virtual
functions)... It is hiding... In fact, it might well be a name conflict
or any other bad thing (behavior is undefined).

"
 17.4.3.1  Reserved names                          [lib.reserved.names]
3 If  the  program  declares  or defines a name in a context where it
is
  reserved, other than as explicitly allowed by this clause, the
behav-
  ior is undefined.
"

"
17.4.3.1.3  External linkage                        [lib.extern.names]

5 Each function signature from the  Standard  C  library  declared
with
  external  linkage is reserved to the implementation for use as a
func-
  tion signature with both extern "C" and extern "C++" linkage,25) or
as
  a name of namespace scope in the global namespace.
"
Your function signature is the same as strlen, and has extern "C++"
linkage in global namespace.
It is reserved for the implementation!
Behavior is undefined!


> There is even no warning after compiling the code.
Behavior is undefined... It might vary from a warning or error at
compile-time to behaving as you expected without any error or warning.

> In front of the
> fact, I have to make a guess that all the C++ compilers are conformed
> to the following rules:
>
> 1) The compiler first compiles all the source file included in the
> project into object files;
>
> 2) At link time, the compiler first searches the object files for all
> the unresolved symbols; if it fails to find some symbols, then the
> compiler will search the libraries which are included in the project to
> find the symbols.
>
> 3) If the object files containes a symbol, then the symbols that have
> the same name in the libraries will be ignored.
>
> Am I correct?
No.
With most compilers (that's not required by the standard) all the
symbol detection is done at compile-time... And there is some symbol
mangling which avoids conflicts at link-time of symbols living in
different namespaces or having different signatures.
All that stuff is non-standard and you can't rely on it.

The only thing that the standard says about your program is that it has
undefined behavior... That is : The standard imposes no limitation on
the behavior that your program can have...

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SuperKoko wrote:
> Lighter wrote:
> > Is overriding a function of a library in accordance with C++ standard?
.
> BTW this is not a question for comp.std.c++ (comp.lang.c++ is more
> appropriate).

I'm not sure I follow that. How could a question about whether the C++
standard allows something not be on-topic for comp.std.c++?

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Is overriding a function of a library in accordance with C++ standard?

The following code is passed by the VS 2005 and Dev C++.

#include <cstdlib>
#include <iostream>

using namespace std;

size_t strlen(const char* p)
{
    return 0;
} // !!! Note this !!! The standard library function strlen is
deliberately overriden.

int main(int argc, char *argv[])
{

    system("PAUSE");

    return EXIT_SUCCESS;
}

There is even no warning after compiling the code. In front of the
fact, I have to make a guess that all the C++ compilers are conformed
to the following rules:

1) The compiler first compiles all the source file included in the
project into object files;

2) At link time, the compiler first searches the object files for all
the unresolved symbols; if it fails to find some symbols, then the
compiler will search the libraries which are included in the project to
find the symbols.

3) If the object files containes a symbol, then the symbols that have
the same name in the libraries will be ignored.

Am I correct?

Any help will be appreciated. Many thanks in advance.

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