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But sometimes, we don’t extend the size of the container, or we can’t know in advance how many elements are to be added.For instance, if the container already has values, and we want to overwrite them starting at the beginning, we would use And we will see an example of a case where we can’t know in advance how many elements are to be added, when we address stream iterators, in a dedicated post. It is typically useful for adding into a container the result of any algorithm that does more than Here we don’t directly have a range to insert into the destination container, therefore we can’t use the range insertion methods.While such iterators are very handy, it is important to realize that in some cases you don’t want to use them.
This really ties in with a similar guideline we saw when searching into a container with the STL.
In the previous lesson, we introduced std::array, which provides the functionality of C ’s built-in fixed arrays in a safer and more usable form.
This may or may not be be overkill depending on whether this code is proven to be a performance bottleneck.
In conclusion, to insert several elements into a container, use the container methods whenever you can.
First, when we resized the array, the existing element values were preserved!
Second, new elements are initialized to the default value for the type (which is 0 for integers).
std::vector lives in the Note that in both the uninitialized and initialized case, you do not need to include the array length at compile time.
This is because std::vector will dynamically allocate memory for its contents as requested.
However, if array is a vector, this won’t happen, because the memory will be deallocated as soon as array goes out of scope (regardless of whether the function exits early or not).
This makes std::vector much safer to use than doing your own memory allocation.