c++: Error: variable length array of non-POD element type

Question

I basically have

int x;
cout << "Please enter how many classrooms there are: ";
cin >> x;
classrooms bunchaClassrooms[x]; //classrooms is a previously declared class.

For some reason it gives the error 'variable length array of non-POD element type 'x'' and I have no idea why, if I were to use a vector of classrooms instead, how could i easily populate it (using a for loop i'm guessing) depending on the user's input.

Simply because variable length arrays are not allowed in C++. (Actually they were planned for C++14 but have eventually been moved to a study group.) — gx_, Nov 09 '13 at 19:00
@g-makulik I would rather say "GCC accepts it _incorrectly_" ;) That's because of an extension (and maybe for C99 compatibility). If you compile with `-std=c++11 -pedantic-errors` (or `-std=c++98 -pedantic-errors`) it rejects it: `error: ISO C++ forbids variable length array ‘bunchaClassrooms’ [-Wvla]`. (Btw for your first question, considering the original error message I think OP is using Clang.) — gx_, Nov 09 '13 at 19:31
@g-makulik Prior to a recent update to Xcode and installing Mavericks — Remy LeBeau, Nov 09 '13 at 20:11

score 7 · Accepted Answer · answered Nov 09 '13 at 19:01

7

You can use std::vector:

std::vector<classrooms> bunchaClassrooms;
for (int i = 0; i < x; ++i)
{
  classrooms c;
  <... enter classrooms info ...>
  v.push_back(c);
}

Array with non-constant boundary isn't good.

answered Nov 09 '13 at 19:01

HEKTO

3,876
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@g-makulik You must not call `resize()` before calls to `push_back()` (but you can call `reserve()` to avoid reallocations). The other way is to call `resize()`, or rather directly construct the vector with a count, then assigning `v[i] = c;`, which closer mimics the use of an array. – gx_ Nov 09 '13 at 20:19
@gx_ Yes of course, just mentioned this because the OP's original question might involve accessing arbitrary elements from the array. – πάντα ῥεῖ Nov 09 '13 at 20:25

score 2 · Answer 2 · answered Nov 09 '13 at 19:00

2

Variable-lengthed arrays is not standard feature of the language. You have to allocate on the heap or create a vector.

answered Nov 09 '13 at 19:00

David G

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c++: Error: variable length array of non-POD element type

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