In one of my programs I was using a for each loop that looked similar to this

for(auto component : components) {
    doSomethingWithComponent(component);
}

and visual studio complained that this would cause the function to use more stack memory than the maximum, so I changed the loop to:

for(int i = 0;i<components.size();i  ) {
    doSomethingWithComponent(components[i]);
}

and the warning went away. Is this because a for each loop generates a reference/copy of the current iteration of object in the loop? But if that is the case, I don't think that a single struct with a few integers would consume that much memory? Is there a reason for this to occur?

EDIT: components is an std::vector if that changes anything

CodePudding user response：

for(auto component : components) {

This is equivalent to having

auto component=components[i];

being performed on each iteration of the loop. A (mostly useless) copy is made of each value in the container, on each iteration of the loop. Hence the stack usage.

This is avoided simply by using a reference:

for(auto &component : components) {

Even better, if the loop is not supposed to modify the contents of the container:

for(const auto &component : components) {

And your C compiler will helpfully complain if, due to a bug, the loop attempts to modify the value in the container.