keeping the same vector throughout the function for additions and deletions

Question

I am creating a vector b1 with fixed size (like c-style array), for copying a1 followed a2. I thought of using assign as below, But size of b1 is reduced to 7(to size of a1) after b1.assign(). How can I keep the b1 size 20 (fixed size) even after assign(). Any suggestions, I am using memcpy() now.

std::vector<int> a1{1,2,3,4,5,6,7};
std::vector<int> a2{ 10,11,12,13,14,15,16,17 };
std::vector<int> b1(20);
b1.assign(a1.begin(),a1.end());

Why not construct the vector from the iterators and then `resize` the vector to the final size you want? — NathanOliver, Aug 23 '17 at 14:25
What happens if the total length of `a1` and `a2` exceeds 20? What do you do with the excess elements? — PaulMcKenzie, Aug 23 '17 at 14:28
Note: if all want to do is concatenate two vectors, then see https://stackoverflow.com/questions/3177241/what-is-the-best-way-to-concatenate-two-vectors — juanchopanza, Aug 23 '17 at 14:31

juanchopanza · Answer 1 · 2017-08-25T20:28:13.283

3

If you want to copy things, you can use std:copy:

std::copy(a1.begin(), a1.end(), b1.begin());

edited Aug 25 '17 at 20:28

answered Aug 23 '17 at 14:25

juanchopanza

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I hope the second argument is a1.end(). And we need to repeat the same for copying a2. – Susanth Aug 25 '17 at 18:21

keeping the same vector throughout the function for additions and deletions

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