What does "expected unqualified-id before numeric constant" mean?

[Allen]

In my app, there is a namespace definition.

...
namespace CMD {
...
const int YT_UP = 1; // line 149
...
};

g++ tells expected unqualified-id before numeric constant error at
line 149.
I change it to be

namespace CMD {
...
const int YT_UP1 = 1; // line 149
...
};

It compiles ok.

So is there name collision for YT_UP?

[Bo Persson]

Allen wrote:
:: In my app, there is a namespace definition.

Probably.

All uppercase names are often used for preprocessor macros, which
doesn't respect namespace scopes. Therefore such names should
generally be avoided for everything else.

Bo Persson