Thread: What is Proper?

The way I was taught C++ looks like this...

Code:

#include <iostream>

using namespace std;

int main()
{

cout<<"Hello World!"<<endl;

//or you could use this to start a new line...

cout<<"Hello World!\n";

system("pause");

}//end main

But after reading the first couple or chapters in a book I have purchased, I noticed that their method is slightly different...
i.e.

Code:

#include <iostream>

int main()
{

std::cout << "Hello World\n";

return 0;

}//end main

What I'm wondering is, is it bad habit to use 'using namespace std;' in place of always typing out that extra 'std::'?

I find that it's faster, but I really want to learn the right way. Also, are the spaces between std::cout, the insertion operator (<<) and the text ("Hello World") important? Or are the optional? I can see them as being a way to make the code more reader friendly, but I don't understand why else they would be needed.

Thanks for the help...

Excellent, that is exactly what I was wondering.

I suppose instead of 'using namespace std;', just stating what I'm using would be faster...

Such as...

Code:

using std::cout;
using std::endl;

One last thing, I noticed that somewhere on this board someone said (sorry for the obscurity, but I can't remember where I saw this :P) that stating what std functions I'm using globally was bad practice... should I state them in each function instead of globally?
Which is faster?

Personally, if you need more then a few of the std commands I just use the entire namespace. I feel that it makes the code more readable and the speed difference is not HUGE, is it?

Originally Posted by jmd15

using namespace std; and std::cout are both proper ways to do it. The std::cout way is faster because it is not loading ALL the std commands into memory(which is what using namespace std does). The std::cout way is directly accessing only that command so it is recommended by some.

well, i dn't think the others will agree with that.

From what i have learned, "using namespace;" defeats the purpose of using namespaces. Hence i'll say that "using namespace;" is NOT really the proper way to do it!

maybe the other more qualified people here can clarify on this.


(check the FAQ for infos about namespaces! There is a good explanation about it there)

Originally Posted by Flakster

One last thing, I noticed that somewhere on this board someone said (sorry for the obscurity, but I can't remember where I saw this :P) that stating what std functions I'm using globally was bad practice... should I state them in each function instead of globally?
Which is faster?

This has nothing to do with speed. The compiler will in both ways generate the same code. Namespaces do not exist in the compiled code. They are just a tool that can help you write safer code. If you pull in a namespace at global scope it's just the same as saying "I don't need that feature, I know what I'm doing".
It's your joice.
Kurt

I like using std::whatever because the more complex code I write, the easier it is to scan my code and know what references are being made to namespaces, classes, whatever.

as a general rule, you should avoid
using namespace blah
directives in header files, but they're not too bad in individual .cpp files. As other peple have mentioned, it makes zero difference to the compiled code.

As for spaces, it's mostly a matter of style. Personnally I like a bit of whitespace, it costs nothing and

cout << "you have " << numApples << " apples;

is more readable then

cout<<"you have "<<numApples<<" apples;

The one big C++ gotcha with white space is when you have a template of templates, e.g.

list<vector<int>/*need a space here*/> listOfIntVectors;

You HAVE to have a space between the '>' characters or C++ will interpret it as a '>>' operator;

This has helped alot guys, thanks.

"using namespace ...;" does not defeat the purpose of using namespaces. You can use a whole namespace and then if you have another namespace that has a function or class with the same name, just qualify it with that namespace when you declare your variables. It's really not a big deal in the real world. The best advice I have, if you are getting a job, is to pick up on the standards of your co-workers. There is nothing more annoying than the new guy coding things in different formats than everyone else. You all need to write your code similarly.