Vector Size change inside loop

[Rajesh78]

Hi,
Can we change the vector size during loop like

vector<int> vec;
vec.push_back(10);
vec.push_back(100);
vec.push_back(1000);
vec.push_back(10000);

for(auto item : vec)
{
        cout<<item<<endl;
        if(item == 10000)
        vec.push_back(5);
}

output
10
100
1000
10000

should not it
10
100
1000
10000
5

if not why?

[2kaud]

The range based for loop is equivalent to

	for (auto item = vec.begin(), ie = vec.end(); item != ie; ++item)
	{
		cout << *item << endl;
		if (*item == 10000)
			vec.push_back(5);
	}

so additions to the end of the vector won't be included as part of the for as the end of the vector is determined at the start of the loop.

Note that 5 has indeed been added to the end of the vector. If

	for (const auto& i : vec)
		cout << i << endl;

is added after the code in post #1 then the display is

10
100
1000
10000
10
100
1000
10000
5

showing that 5 has indeed been added.

Note that if a relocation happens because there is insufficient capacity within the existing vector, then all iterators are invalidated as part of the relocation. So performing operations within a loop like this that may invalidate iterators is not recommended and is not guaranteed to work correctly if a relocation occurs.