namespace without name. I do not understand

[geouser]

Why would I write a namespace without name:

namespace
{
double d = 88.22;
}

And not directly:

double d=88.22;

Both are considered definitions of global variables...

[Repeater]

This is known as an "anonymous namespace".

From outside the file, the objects inside the anonymous namespace are invisible. This is a way to restrict visibility to one file.

[Peter87]

In other words, d will have internal linkage.

namespace { double d = 88.22; } is essentially the same as static double d = 88.22;

[jonnin]

if it helps, I have never felt compelled to do this. I personally name all my namespaces, structs, classes, and enums etc. and have found nameless stuff to be more annoying than useful in general. I don't really like the namelessness of lambdas either, but its going to be hard to avoid those going forward I think.

[Repeater]

I have found nameless things to be very useful in situations where I don't want any other parts of the codebase to use them. Horses for courses.

[z05DSL3A]

Peter87 wrote:

In other words, d will have internal linkage.

Doesn't it still have external linkage, just looks like internal linkage due to the anonymous namespace actually having a hidden unique name?

[Peter87]

No, the standard says it has internal linkage.

http://eel.is/c%2B%2Bdraft/basic.link#6

[z05DSL3A]

Okay, I was getting confused by a footnote attached to the section on unnamed namespace...

Although entities in an unnamed namespace might have external linkage, they are effectively qualified by a name unique to their translation unit and therefore can never be seen from any other translation unit

.