Question

I’m using in my code many namespaces including the std one , so when I want to declare a string variable in my code should I precise std::string or I can just put string :

#include <string.h> 

using namespace std;
using namespace boost;
using namespace xerces;

int main()
{
    /*! should I declare my str like this */
    std::string str;
    /*! or I can declare it like this */
    string str1;
    cout << str << str1 <<endl;
    return 0;
}

Answer 1

Since you have using namespace std;, the name string means the same as std::string[*]. It’s therefore a question of style which you prefer (and if you prefer std::string then you can leave out using namespace std;).

There are some name clashes between std:: and boost::, in particular for things that were trialled in Boost prior to standardization. So for example if you include the appropriate headers then both std::shared_ptr and boost::shared_ptr exist. They may or may not refer to the same type, I haven’t checked whether Boost tries to detect the standard type before defining its own.

So it’s not necessarily a good idea to use both std and boost namespaces at the same time. You can use individual names with using std::string;, instead of the whole namespace.

[*] if std::string is defined, which it isn’t, since you didn’t include <string>.