Push_back function for Class defined vector

Question

I have a vector that takes in class values of a class called Bug which stores a mass and number of legs for each instance. I'm having trouble using the push_back function, and suspect it's just a syntax issue, but can't figure out exactly what I'm doing wrong. I am trying to add 3 more values into the end of the vector. Here is my partial code:

std::vector<Bug> bugs(5); //vector definition
bugs.push_back(3);

@user1438832 what would the syntax be for this? Just replace push_back with emplace_back? — Cayden, Jan 12 '17 at 05:55
`push_back()` adds only one element. If you want to add 3 more elements, either call `push_back()` 3 times or call `resize()` with the appropriate new size you want. — Cornstalks, Jan 12 '17 at 05:56
@Cornstalks Thats exactly what I was looking for, I was unaware of the resize function. Thanks! — Cayden, Jan 12 '17 at 05:58

score 4 · Accepted Answer · edited Jan 12 '17 at 06:30

if you are trying to add 3 default constructed Bugs, you will need to call push_back 3 times:

struct Bug{};  
std::vector<Bug> bugs(5); //vector instantiation 
bugs.push_back(Bug{});
bugs.push_back(Bug{});
bugs.push_back(Bug{});

You can also use emplace_back(c++11). It expects constructor arguments.
In this case, no arguments:

struct Bug{};  
std::vector<Bug> bugs(5);
bugs.emplace_back();
bugs.emplace_back();
bugs.emplace_back();

Apart from using a loop, you can add N new elements using resize:

bugs.resize(bugs.size()+n);

Push_back function for Class defined vector

1 Answers1