On Wed, Dec 11, 2013 at 3:03 AM, wrote:
> Dears,
> I have a test.proto file like this:
>
> message Test {
> optional string str_1 = 1;
> optional string str_2 = 2 [default="3.0"];
> }
>
> A default value is set for string field str_2. In the main file I defined
> a global Test instance and access str_2 in main function like this:
>
> #include "..."
>
> Test g_test;
> int main(int argc, char** argv) {
> cout << g_test.str_2().c_str() << endl; // This should output "3.0"
> but I got sigsegv under some situations.
> }
>
> As the comment suggested, I got sigsegv under certain situations. I looked
> into the code generated by protoc version 2.5, in the constructor of Test,
> str_2 was pointed to _default_str_2_, which is NULL at the beginning and
> initialized by another global variable(named
> static_descriptor_initializer_test_2eproto_)'s constructor.
> So, if the global variable defined by me (g_test) was initialized
> after static_descriptor_initializer_test_2eproto_, the above code would
> work as expected. However, if static_descriptor_initializer_test_2eproto_
> is initialized after g_test, then g_test.str_2 will point to NULL and cause
> sigsegv when accessed.
>
> Is this an intended behavior? Which means I should avoid using global
> instance of message that have a string field with default value?
>
I think this is a bug in protobuf code. Nonetheless, you'd better avoid
using global variables of class type. Such usage is explicitly forbidden by
Google C++ style guide for exactly the problem you see here.
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