using the vector template class

[Rupert Wood]

David Churches wrote:

> I am trying to use GCC to compile C++ code, but I am unable to use 
> various classes such as vector and valarray. To illustrate this, I
> have been trying to compile the following piece of very simple code.
:
> #include <vector>
> 
> int main ()
> {
> 
>    vector <int> ivec(5);
>    return 0;
> }

libstdc++-v3's headers (correctly) only define vector in the 'std'
namespace and not the global namespace: i.e. you must qualify 'vector'
with 'std::'

    #include <vector>

    int main ()
    {
        std::vector<int> ivec(5);
        return 0;
    }

or import std::vector into the global namespace:

    #include <vector>
    using std::vector;

    int main ()
    {
        vector<int> ivec(5);
        return 0;
    }

or import the whole std namespace:

    #include <vector>
    using namespace std;

    int main ()
    {
        vector<int> ivec(5);
        return 0;
    }

I prefer the first or second solution for source files (depending on how
much 'vector' et al are used) but always the first solution for header
files - IMO, a header file should not pollute namespaces of a source
file that includes it. The third solution is perhaps the simplest but
often regarded as poor style: it is less precise that the other two.

Hope that helps,
Rupert.