# V2575. MISRA. The global namespace should only contain 'main', namespace declarations and 'extern "C"' declarations.

This diagnostic rule is based on the software development guidelines developed by MISRA (Motor Industry Software Reliability Association).

This diagnostic rule is only relevant to C++. Declarations in the global space clutter the list of available identifiers. New identifiers added to the block's scope may be similar to identifiers in the global space. This can confuse a developer and lead to incorrect identifier choice.

To guarantee the developer's expectations, all identifiers must be located inside the corresponding namespaces.

The analyzer issues a warning for the following code example:

    int x1;
    void foo();

According to the rule, this code should look like this:

    namespace N1
    {
      int x1;
      void foo();
    }

Another possible version with the extern "C" may look like this:

    extern "C"
    {
      int x1;
    }
    extern "C" void bar();

Here is what the MISRA standard suggests. If the name of the type alias contains the size of its final type, we can use 'typedef' in the global namespace.

The analyzer doesn't issue warnings for the following code example:

    typedef short int16_t;
    typedef int INT32;
    typedef unsigned long long Uint64;

The analyzer issues warnings for the following code example:

    typedef std::map<std::string, std::string> TestData;
    typedef int type1;

This diagnostic is classified as:

MISRA-CPP-2008-7.3.1