cplusplus.co.il

#include <vector>
using std::vector;

int main () {
    vector<int> v1;  // option 1
    vector<int> v2(); // option 2
}

Posted in questions | 1 Comment

One Response

1. on 20/04/2010 at 22:59 | Reply Or

   Yes, it’s called The Most Vexing Parse, and it is a really vexing one. When you say vector v2() you are actually importing an external function(named v2 and that returns a vector of ints and has no parameters) from another translation unit.
   This can be even more vexing if you write:
   Suppose you want to read a file which his name stored in a variable filename, and copy it directly into a new vector:

   vector<int> v(istream_iterator<int>(filename), istream_iterator<int>());
   

   Although it is somehow not trivial example, that will be parsed by the vexing c++ compiler as a function declaration (because the parenthesis can be omitted to get a function declaration), not a vector initialization. to remedy the situation we have to do something like the following:

   istream_iterator<int> begin(filename);
   istream_iterator<int> end;
   vector<int> v(begin, end).
   

   Thanks!