I want to declare a couple of variables in a for loop:
for ( int x = 0, int y = 0 ; ; )
{
}
,but this doesn't work since I can't specify a type after the comma ,. In this case, removing the second int or declaring y outside the loop would fix the problem, but what if I want to declare both variables inside the loop and also have different types?
Can I have something like:
for ( int x = 0, float y = 0 ; ; )
{
}
?
This is impossible; the C++ grammar just won't admit it. The closest you can get to this is putting an extra scope around the loop:
{
int x;
float y;
for (x=0, y=0;;) {
}
}
no, you can only declare variables of one type in there. What you could do is work around this issue with std::pair, std::touple or some similar construct:
for(std::pair<int, float> p = std::make_pair(0, 0.0f);; )
{
p.first++;
p.second *= 0.5f;
}
pair/touple. I would still caution that this seems like a strange use of a for statement. If one of the variables isn't specifically used for constraining the iteration, it shouldn't be mashed into the for.
C++ allows you to do this:
for( struct {int x; float y;} s; s.x<10; s.x++,s.y*=2.0f) {
}
MSVC has a bug such that it does not allow this, but more standards compliant compilers allow it.
No, that's not possible, they all have to be of the same type.
You can't.
My suggestion would be to split the code inside into a separate function to keep it readable:
template<typename O, typename I>
O copy(I in, I end, O out) {
for(; in != end; ++in, ++out)
*out = *in;
return out;
}
IMO, this is much nicer than inventing a new scope or extending the lifetime of iterators, plus it makes you think whether the code can be genericized.
