Can I use break to exit multiple nested for loops?

Question

Is it possible to use the break function to exit several nested for loops? If so, how would you go about doing this? Can you also control how many loops the break exits?

Answer 1

One nice way to break out of several nested loops is to refactor your code into a function:

void foo()
{
    for(unsigned int i=0; i < 50; i++)
    {
        for(unsigned int j=0; j < 50; j++)
        {
            for(unsigned int k=0; k < 50; k++)
            {
                // If condition is true
                return;
            }
        }
    }
}

Answer 2

AFAIK, C++ doesn't support naming loops, like Java and other languages do. You can use a goto, or create a flag value that you use. At the end of each loop check the flag value. If it is set to true, then you can break out of that iteration.

Answer 3

A code example using goto and a label to break out of a nested loop:

for (;;)
  for (;;)
    goto theEnd;
theEnd:

Answer 4

break will exit only the innermost loop containing it.

You can use goto to break out of any number of loops.

Of course goto is often Considered Harmful.

is it proper to use the break function[...]?

Using break and goto can make it more difficult to reason about the correctness of a program. See here for a discussion on this: Dijkstra was not insane.

Answer 5

No, don't spoil it with a break. This is the last remaining stronghold for the use of goto.

Answer 6

Other languages such as PHP accept a parameter for break (i.e. break 2;) to specify the amount of nested loop levels you want to break out of, C++ however doesn't. You will have to work it out by using a boolean that you set to false prior to the loop, set to true in the loop if you want to break, plus a conditional break after the nested loop, checking if the boolean was set to true and break if yes.