std::vector reserve / constructor question

[Chris Roth]

When I create a vector with:

vector<double> v(10);

am I right to assume that it has initialized ten elements with the
number zero?

What if I want to just make space for 10 elements I'll add in later? Is
the best way to do that:

vector<double> v;
v.reserve(10);

That is to say, there is no constructor that reserves space without
entering values (default or otherwise), right?

 

[mlimber]

When I create a vector with:

vector<double> v(10);

am I right to assume that it has initialized ten elements with the
number zero?

What if I want to just make space for 10 elements I'll add in later? Is
the best way to do that:

vector<double> v;
v.reserve(10);

That is to say, there is no constructor that reserves space without
entering values (default or otherwise), right?

Right, unfortunately.

Cheers! --M

 

[Mark P]

When I create a vector with:

vector<double> v(10);

am I right to assume that it has initialized ten elements with the
number zero?

Yes. The technical term here is that the elements are
"value-initialized" which, for built-in types, is the same as
zero-initialized.

What if I want to just make space for 10 elements I'll add in later? Is
the best way to do that:

vector<double> v;
v.reserve(10);

That works fine.

That is to say, there is no constructor that reserves space without
entering values (default or otherwise), right?

Yes.