Is there an equivalent to the “for … else” Python loop in C++?

Question

Python has an interesting for statement which lets you specify an else clause.

In a construct like this one:

for i in foo:
  if         


        

Answer 1

There is no such language construct in C++, but, thanks to the "magic" of the preprocessor, you can make one for yourself. For example, something like this (C++11):

#include 
#include 
using namespace std;

#define FOR_EACH(e, c, b) auto e = c.begin(); for (; e != c.end(); ++e) {b} if (e == c.end()) {}

int main()
{
    vector v;
    v.push_back(1);
    v.push_back(2);

    FOR_EACH(x, v, {
        if (*x == 2) {
            break;
        }        
        cout << "x = " << *x << " ";
    })
    else {
        cout << "else";
    }

    return 0;
}

This should output x = 1 else.

If you change if (*x == 2) { to if (*x == 3) {, the output should be x = 1 x = 2.

If you don't like the fact that a variable is added in the current scope, you can change it slightly:

#define FOR_EACH(e, c, b, otherwise) {auto e = c.begin(); for (; e != c.end(); ++e) {b} if (e == c.end()) {} otherwise }

then use would be:

FOR_EACH(x, v, {
    if (*x == 2) {
        break;
    }        
    cout << "x = " << *x << " ";
},
else {
    cout << "else";
})

It's not perfect, of course, but, if used with care, will save you some amount of typing and, if used a lot, would become a part of the project's "vocabulary".