Is 'auto const' and 'const auto' the same?

Question

Is there a semantic difference between auto const and const auto, or do they mean the same thing?

Solution 1

The const qualifier applies to the type to the immediate left unless there is nothing to the left then it applies to the type to the immediate right. So yup it's the same.

Solution 2

Contrived example:

std::vector<char*> test;
const auto a = test[0];
*a = 'c';
a = 0; // does not compile
auto const b = test[1];
*b = 'c';
b = 0; // does not compile

Both a and b have type char* const. Don't think you can simply "insert" the type instead of the keyword auto (here: const char* a)! The const keyword will apply to the whole type that auto matches (here: char*).

Comments

[Seshadri R]

If there is nothing left, then it is right (and vice versa) :-)

[Arne Vogel]

That's not really how it works, specifiers and qualifiers (that precede the declarator) may appear in any order, e.g. long volatile unsigned const typedef long cvull;. The type is neither (fully) to the left nor to the right of const.

[4LegsDrivenCat]

@ArneVogel OMG, why typedef is allowed in the middle :)

[jbruni]

The const doesn't really apply to char*, it applies to the char part, not the * part.

[WillY]

As @ArneVogel commented, the answer is not completely correct. The fact that this is the accepted answer is misleading (and possibly dangerous).

[Krapnix]

@ArneVogel where could I read more about this please