How to use std::vector.insert()?

Question

So, I'm trying to learn how to use std::vectors , but I have a problem:

std::vector<Box>entities;

entities.insert(1, Box(&world, b2Vec2(Camera.getCenter().x, Camera.getCenter().y), b2Vec2(25, 25), 0, sf::Color::Red, b2_dynamicBody, 1.0f, 0.3));

How come that doesn't work? It gives me the following error :

Error no instace of overloaded function "std::vector<_Ty, _alloc>::insert [with _Ty=Box, _Alloc=std::allocator<Box>] matches the argument list. Argument types are (int, Box). Object type is std::vector<Box, std::allocator<Box>>

What am I doing wrong?

Answer 1

The first parameter should be an iterator, not an index. You can get an iterator to position 1 by using entities.begin() + 1 .

Note that position 1 is the location of the second element in the vector: vector indexing is zero-based .

Answer 2

The first parameter is wrong. You should specify an iterator , not an index.

entities.insert(entities.begin() + i, theItem);

where i is the position you want to insert at. Note that the vector must be at least of size i .

Answer 3

entities.insert(entities.begin(), /*other stuff as before*/ would insert at the beginning of your vector. (ie the zeroth element). Remember that vector indexing is zero-based.

entities.insert(1 + entities.begin(), /*other stuff as before*/ would insert at the second spot.

Answer 4

All overloaded versions of the method insert require that the first argument would be of type std::vector<Box>::const_iterator applied to your vector definition. This iterator specifies the position where a new element must be inserted.

However you are passing in an integer value 1 instead of the iterator

entities.insert(1, 
               ^^^
                Box(&world, b2Vec2(Camera.getCenter().x, Camera.getCenter().y),
                    b2Vec2(25, 25), 0, sf::Color::Red, b2_dynamicBody, 1.0f, 0.3));

There is no implicit conversion from an object of type int to an object of type std::vector<Box>::const_iterator . So the compiler issues an error.

Maybe you mean the following

#include <vector>
#include <iterator>

//...

entities.insert( std::next( entities.begin() ), 
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
                Box(&world, b2Vec2(Camera.getCenter().x, Camera.getCenter().y),
                    b2Vec2(25, 25), 0, sf::Color::Red, b2_dynamicBody, 1.0f, 0.3));

Or if your compiler does not support function std::next then you can jjust write

entities.insert( entities.begin() + 1, 
                 ^^^^^^^^^^^^^^^^^^^^^
                Box(&world, b2Vec2(Camera.getCenter().x, Camera.getCenter().y),
                    b2Vec2(25, 25), 0, sf::Color::Red, b2_dynamicBody, 1.0f, 0.3));