What is wrong with using a static member object with a class?

Question

I have heard that using static member objects is not a very good practice.

Say for example, I have this code:

class Foo {
...
static MyString str;
};

I define and initialize this variable in the implementation file of this class as:

MyString Foo::str = "Some String"; // This is fine as my string API handles this.

When I run this code, I get a warning:

warning:'Foo::str' requires global construction.

I have quite much of such members in my class, what is the best way to handle this.

Thanks,

Answer 1

Most of the arguments against them are the same as for global variables:

1. Initialization order between different compilation units is undefined.
2. Initialization order inside one compilation unit may affect the behavior — thus non trivial ordering may be required.
3. If a constructor throws an exception you can't catch it, your program is terminated.

APPENDED: To handle this properly you must either make sure that above points don't apply to your code and ignore the warning, or redesign your program: Do you really need them static? Why not use const char* Foo::str = "Some String";?

Answer 2

The biggest reason for concern with this example is that constructing the static member object happens before main() and destruction happens after main() (or when you call exit()). So far, that's a good thing. But when you have multiple objects like this in your program, you risk a bug where code attempts to use an object that has not yet been constructed or has already been destroyed.

The C++ FAQ Lite has some helpful discussion on this topic, including a workaround/solution. Recommended reading is questions 10.14 through 10.18. 10.17 is most directly applicable to your example.