CODEWITHSUNDEEP
c++vector
CodersSC
CodersSC

Reputation: 710

trying to copy all the elements of a vector

I have two vectors 

typedef std::vector<std::string> messages;
typedef std::vector<std::string> addMessage;
messages st;
addMessage additionlMsgs;

when the user inputs a string i then split that string by a certain character which is then splitted into st

i want to copy that vector over to additionalMsgs at some point but i get a run time error i cannot see why.

i try to copy it over as follows

 copy(st.begin(), st.end(), additionlMsgs.begin());

can you see anything that is incorrect?

Thanks Shamari

Upvotes: 0

Views: 132

Answers (3)

Lucretiel
Lucretiel

Reputation: 3354

Using resize is probably a better option in this case.

additionlMsgs.resize(messages.size());
copy(st.begin(), st.end(), additionlMsgs.begin());

This is because additionalMsgs only gets reallocated once, as opposed to multiple times when back_inserter is used.

Upvotes: 0

ronag
ronag

Reputation: 51283

If you want to append:

additionlMsgs.insert(additionlMsgs.end(), st.begin(), st.end());

If you want to overwrite:

additionlMsgs = st;

Upvotes: 3

NPE
NPE

Reputation: 500883

It sounds like you're looking for std::back_inserter:

std::copy(st.begin(), st.end(), std::back_inserter(additionlMsgs));

That'll append to additionlMsgs. If you wish to overwrite its contents, you might want to use:

additionlMsgs = st;

The code you have right now never adds new elements to additionlMsgs; it simply overwrites existing ones without performing any bounds checking. If additionlMsgs is too short, you get undefined behaviour.

Upvotes: 4

Related Questions