When is memory allocated for a vector?
Greetings,
I have a short question. If I simply declare a std::vector of N doubles, i.e.
,
when will the memory of N doubles be allocated? Right at this point, or only if I fill this vector with actual double values?
I have a short question. If I simply declare a std::vector of N doubles, i.e.
|
|
when will the memory of N doubles be allocated? Right at this point, or only if I fill this vector with actual double values?
> only if I fill this vector with actual double values?
On construction, the vector is filled with N zero initialised values of type double
On construction, the vector is filled with N zero initialised values of type double
You can also construct a sized vector with a value other than the default.
This creates a vector with N elements all initialized to 5.3.
http://www.cplusplus.com/reference/vector/vector/vector/
std::vector<double>(N, 5.3);This creates a vector with N elements all initialized to 5.3.
http://www.cplusplus.com/reference/vector/vector/vector/
It's interesting to consider what happens when you add a bunch of values to a vector. You probably know that it doesn't allocate new space for the items 1 at a time. That would be really inefficient. Instead it doesn't does* something like adding 50% more space when it needs it. You can see the extra space with the capacity() method.
When it allocates that (hypothetical) 50%, it does NOT create items in the new space. That would be inefficient. Instead, when you add a new item, it constructs the new item in the appropriate location in the buffer.
* Thank you seeplus for the PM reporting my blunder.
When it allocates that (hypothetical) 50%, it does NOT create items in the new space. That would be inefficient. Instead, when you add a new item, it constructs the new item in the appropriate location in the buffer.
* Thank you seeplus for the PM reporting my blunder.
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