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;
}
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>.
string, and it doesn't clash with any other definition of string, then first do either using namespace std; or using std::string;. I prefer using std::string;, because I don't like to import a great long list of names, some of which I've never heard of, and that might change in a future compiler release.You can just write string. But what if boost or xerces also have a symbol string? I would advise against using these using directives. It is not only string that could clash. You are essentially pulling a whole lot of symbols into the global namespace. If you really want to avoid typing std:: then you can use a typedef:
typedef std::string MyStr;
strong, meaning to type std::string and there's a boost::strong?
set function, as in a question I saw recently.Usually it is not needed to specify std::string if you have declared using namespace std; BUT as a general case, if there are multiple namespaces which contain different classes with the same name, then you will have to specify the namespace next to the type (namespace::type) regardless of the existence of the using statement.
You are using the namespace std so you do not NEED to prepend string with std:: but you CAN if you want.
A good way to code is not to use any relevant namespace in headers, in order to prevent exposing the namespaces outer when #include. But in compiled source, you can do whatever you want, even using the std namespace and call std::string. Sometimes it's even needed (if you include two namespaces that define the same string class).
usingis for :)#include <string.h>doesn't bring youstd::stringdeclarationusingis abused.