break; C++: which loop is it actually breaking

Question

simple question regarding C++ code:

for(int i=0;i<npts;i++)
{
    for(int j=i;j<2*ndim;j++)
    {
        if(funcEvals[i]<bestListEval[j])
        {
            bestListEval[j] = funcEvals[i];
            for(int k=0;k<m_ndim;k++)
                bestList[j][k] = simplex[i][k]; 
            break; 
        }
    }
}

I want to ensure that

• Each line of double **simplex is inserted at most once in double **bestList
• The instance of break here breaks out of the second (inner) for loop.

Is this the case?

Answer 1

The break statement in C++ will break out of the for or switch statement in which the break is directly placed. In this case it will break out of the for (int j = ... loop.

There is no way in C++ to have break target any other loop. In order to break out of parent loops you need to use some other independent mechanism like triggering the end condition.

// Causes the next iteration of the 'for (int i ...' loop to end the loop)
i = npts;

// Ends the 'for (int j ...' loop
break;

Answer 2

The break statement in C++ will break out of the for or switch statement in which the break is directly placed. It breaks the innermost structure (loop or switch). In this case:

    for(int i=0;i<npts;i++)
    {
        for(int j=i;j<2*ndim;j++)
        {
            if(funcEvals[i]<bestListEval[j])
            {
                bestListEval[j] = funcEvals[i];
                for(int k=0;k<m_ndim;k++)
                    bestList[j][k] = simplex[i][k]; 
                break; 
            }
        }
        // after the 'break' you will end up here
    }

There is no way in C++ to have break target any other loop. In order to break out of parent loops you need to use some other independent mechanism like triggering the end condition.

Also, if you want to exit more than one inner-loop you can extract that loops into a function. In C++ 11 lambdas can be used to do it in-place - so there will be no need to use goto.

Answer 3

You are breaking out of your second loop to your first loop.

for (int i=0; i<npts; i++)

You could set a boolean at the top

bool shouldBreak = false;

and when you write break, write

shouldBreak = true;
break;

Then at the end of your loop, check each time,

if (shouldBreak) break;