Note that if the size of the vector is greater than the biggest number an int can represent, size will contain an implementation defined (de facto garbage) value. Using.size refers to the function (for example if you want to take it's address) where as.size() calls the function You initialize the size when you have a good idea of the number of elements that you need to store in the vector
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If you are retrieving data from database or other source for instance that you know has 1000 elements in it then it makes sense to go ahead and allocate the vector with an internal array that will hold that much data.
187 i have a vector<customclass*> and i put a lot of items in the vector and i need fast access, so i don't use list
How to set initial size of vector (for example to be 20 000 places, so to avoid copy when i insert new)? 75 there is no way to define a constant size vector If you know the size at compile time, you could use c++11's aggregate. What exactly a call to std::vector::size does depends on the particular implementation of the standard library
However, the standard places several constraints on what it can and cannot do In particular, it requires a call to size to execute in constant time, which means it cannot count the elements (that would be linear in the container size, not constant) Vector in stl is a class template, when you give template parameter inside <sometype> following vector, c++ compiler generated code for a class of type sometype So when you populate the vector using push_back, you are actually inserting another object of sometype so when you request.size() from the compiler it gives you the number of sometype objects inserted by you
The size of a vector is the number of elements that it contains, which is directly controlled by how many elements you put into the vector
Capacity is the amount of total space that the vector has. How do i find the size of a 2 dimensional vector So far i have the following code which doesn't compile #include <iostream> #include <vector> using namespace std
The sizeof operator returns the size in bytes of the object or expression at compile time, which is constant for a std::vector. 3 std::vector::size is a member function You have to call it and it returns the size of the vector You want to use.size() not.size
