Question

I am unable to see what is wrong in the following (very contrived) code. It might be the way I have declared a size 2 vector inside the mystruct. But isn’t that how we declare a vector of size 2 whose contents we have yet to initialize?

struct mystruct
{
  int a;
  int b;
  vector<double> c(2);    };

   int main(int argc, char *argv[])
{
  mystruct test;
  (test.c)[0]=3.4;
  (test.c)[1]=1.8;
  return 0;    }

The compiler is throwing me the following error message:

g++ -Wall simple.cpp

simple.cpp:18: error: expected identifier before numeric constant

simple.cpp:18: error: expected ‘,’ or ‘…’ before numeric constant

simple.cpp: In function ‘int main(int, char**)’:

simple.cpp:32: error: invalid types ‘[int]’ for array
subscript

simple.cpp:33: error: invalid types ‘[int]’ for array subscript

Answer 1

You cannot initialize mystruct::c in the class definition, this has to be done in the constructor.

struct mystruct {
  mystruct() : c(2) { }
  vector<double> c;
};