Re: Undefined symbol error for static const char

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 8 Oct 2009 14:05:00 -0700 (PDT)

Message-ID:

<89d047a6-a3fd-45b4-93cd-afa4b4fd5d44@m18g2000vbs.googlegroups.com>

On Oct 8, 3:20 pm, Pete Becker <p...@versatilecoding.com> wrote:

rawhm wrote:

What gives?

$ cat sc.cpp

#include <vector>

class cls {
public:
    static const char foo = 100;
};

int main(int argc, char **argv) {
    std::vector<char> vect;

    vect.resize(10, cls::foo);
    return 0;
}

$ g++ sc.cpp

Undefined symbols:
"cls::foo", referenced from:
__ZN3cls3fooE$non_lazy_ptr in ccB49b7c.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

And the linker is right: it's not defined. Roughly speaking,
if your code takes its address (and that includes passing it
by reference) you have to define it.

const char cls::foo; // definition

The declaration in the class definition is a declaration, not
a definition.

To which I might add (considering that others have mentionned
that it does compile and link successfully with certain versions
of g++): not providing the definition is undefined behavior; the
compiler doesn't have to reject the code. In fact, your results
are likely to vary depending on whether vector::resize is inline
or not, and the level of optimization.

--
James Kanze