Editing C++ (section)

===Prefer iostreams to printf and scanf===

Most developers are familiar with the C-style printf statement syntax, for example:

 printf ("The result is %d\n", i);

The drawback of this approach is that the formatting code depends on the type of i.  Even worse, it may vary depending on the OS and whether we are using 32 bit or 64 bit.  For example. maybe that formatting code should be "%ld" or "%lld" or "%Ld".  The first is for long ints, the second for long long ints, and the third is system dependent.  Which would you use for a 64 bit length integer?  The answer to that is system dependent.  Since we compile our code on many systems, and both as 32 bti and 64 bit, it is important to avoid this conundrum.  (In templated code this situation is even worse).

The C++ iostream equivalent to the above is:

 std::cout << "The result is " << i << "\n";

Now the compiler will make the right conversion for us, regardless of what <tt>i</tt> is.  More complicated printf style formatting can also be converted to iostrings, for example:

 printf ("The result is %.3f\n", x);

becomes

 std::cout << "The result is " << setprecision(3) << x << "\n";

On the other hand, the standard C++ stream formatting modifiers like this example, although overloaded to correctly match the variable type, tend to be overly verbose to conveniently use.

I recommend therefore using boost::format where specific formatting is required.  It is overloaded and will correctly match the variable type and length, but can be used with the familiar and concise POSIX format strings.   boost::format has already been adopted in the next official C++ standard.  Here is an example using boost::format:

 std::cout << format("The result is %.3f\n") % x;