Using a header file instead of the standard namespace

Question

I am curious if there is any header file in C++ which can be used (included) instead of the standard namespace (namespace std) that works the same even in new versions of C++? I want to know if I can write code without using any namespaces and still be able to use the string data type.

• Tony The Lion: Why don't you want to add namespaces?
• Cat Plus Plus: Don't use using namespace std and no, because it's a terrible idea
• Mats Petersson: I'm guessing, because there is a bunch of old code that doesn't have namespace qualifiers.
• Mo Sanei: I want it to be compatible with old C++ code but I can't use <iostream.h> because my compiler is not old.
• Puppy: The only way to fix old code is to fix it.

Answer 1

string is in the std namespace, so you can't completely disregard it.

There are options though:

using std::string;
using namespace std;
typedef std::string myString;
//or fully qualify the name
std::string mystr;

which you can put in a header and include that.

There, now I gave you the recipe for disaster. Don't use it!

Namespaces are good. Learn to use them, rather than hacking your way around them.

• Bartek Banachewicz: using std::string; at least makes it clear that "I need one specific part a lot", rather than "lololo, bring teh codez on". (Still, don't put it in headers)
• Mo Sanei: What is the difference between "std::string MyString" and "typedef std::string MyString" in functionality?
• Luchian Grigore: @MohammadSanei the first creates a variable, the second defines a type.
• Mo Sanei: So then I'll be able to use MyString as a shorthand for std::string?

Answer 2

Headers and namespaces are not related, and namespaces are good things. using namespace std is bad. You can always use the std::string data type without using namespace std;.

Answer 3

To use "using namespace std;" is a poor idea (although I have to admit I do this rather regularly in my samples I post here, for ease of typing). To hide the same in a header file is an even worse idea.

Namespaces are there for a reason.

But if you have, say, 100000 lines of already existing code that is written pre-namespace standard, and you quickly want to port that to use in a new compiler, then adding "using namespace std;" to the top of each file would be the preferred solution.

Answer 4

You could typedef the classes you wish to use, but this is a really bad idea.

#include <string>
typedef std::string string;

• Charles Beattie: using std::string; is the preferred way of bringing string into the current namespace.
• Open AI - Opting Out: Yes, I know. But they didn't want to use using, and it's not good to pollute a header with using, either. Although, saying that, I'm just polluting with a different typename instead.
• Mo Sanei: That's perfect! I just got what you were saying! Is there any way to define cout and endl in a similar way inside a header file without polluting it with using?
• Open AI - Opting Out: It's a perfectly terrible idea.
• Mo Sanei: Is there any way to define cout in a similar way?