Adding an element to a Vector while iterating over it - c++

Question

As the title says, I want to add an element to a std::vector in certain cases while iterating through the vector. With the following code, I'm getting an error "Debug assertion failed". Is it possible to achieve what I want to do?
This is the code I have tested:
#include <vector>
class MyClass
{
public:
MyClass(char t_name)
{
name = t_name;
}
~MyClass()
{
}
char name;
};
int main()
{
std::vector<MyClass> myVector;
myVector.push_back(MyClass('1'));
myVector.push_back(MyClass('2'));
myVector.push_back(MyClass('3'));
for each (MyClass t_class in myVector)
{
if (t_class.name == '2')
myVector.push_back(MyClass('4'));
}
return 0;
}
EDIT:
Well, I thought for each was standard C++, but it seems that it's a Visual Studio feature:
for each, in
Visual c++ "for each" portability

Answer 1

The act of adding or removing an item from a std::vector invalidates existing iterators. So you cannot use any kind of loop that relies on iterators, such as for each, in, range-based for, std::for_each(), etc. You will have to loop using indexes instead, eg:
int main()
{
std::vector<MyClass> myVector;
myVector.push_back('1');
myVector.push_back('2');
myVector.push_back('3');
std::vector<MyClass>::size_type size = myVector.size();
for (std::vector<MyClass>::size_type i = 0; i < size; ++i)
{
if (myVector[i].name == '2')
{
myVector.push_back('4');
++size; // <-- remove this if you want to stop when you reach the new items
}
}
return 0;
}

Answer 2

As pointed out by pyon, inserting elements into a vector while iterating over it (via iterators) doesnt work, because iterators get invalidated by inserting elements. However, it seems like you only want to push elements at the back of the vector. This can be done without using iterators but you should be careful with the stop condition:
std::vector<MyClass> myVector;
size_t old_size = myVector.size();
for (int i=0;i<old_size;i++) {
if (myVector[i].name == '2') { myVector.push_back(MyClass('4')); }
}

Answer 3

After following the previous answers, you can use const auto& or auto& to have clean code. Should be optimized in release build by the compiler.
std::vector<MyClass> myVector;
std::vector<MyClass>::size_type size = myVector.size();
for (std::vector<MyClass>::size_type i = 0; i < size; ++i)
{
const auto& element = myVector[i];
element.do_stuff();
}