Just What Is This TR1 Thing?

Visual CPP Team

Hi there. Rob Huyett here again. I’m an SDET on the VC Libraries team. One of the things I’ve been working on lately is the new TR1 add-on for Visual Studio 2008. When VS 2008 TR1 support was announced about a month ago, I’m sure that the reaction varied from “Woo-hoo! I can’t wait!” to “Huh? What’s TR1? Do I care about this?” and all sorts of things in between.

This post is mostly aimed at that second category of folks – the ones who hadn’t heard about TR1, and who maybe haven’t found the time or inspiration to seek out what it’s all about. I’ll talk briefly here about just what TR1 is, and I’ll describe just a few of the TR1 features that I think are particularly nifty. This isn’t going to be an in-depth discussion or how-to manual, but it will hopefully inspire someone out there to take a closer look at what’s in TR1 and see if it can help you in your projects.

So what is TR1? Well, TR1 (“Technical Report 1”) is a set of proposed additions to the C++0x standard. Most of it will likely find its way into the new standard, but in the meantime it provides a useful stepping stone toward C++0x. TR1 is full of very useful new utilities such as new types of smart pointers (called “shared_ptr” and “weak_ptr”), new containers (tuples, unordered maps, unordered sets, and a neat STL-like array), reference wrappers, regular expression support, and function wrappers. You might look at that list and think that much of it sounds familiar. Smart pointers and function wrappers, for instance, already exist. This is true, but TR1’s versions try to be easier to use and more useful than the existing stuff… sort of like the next iteration based on a few years of experience finding out what works and what doesn’t work.

Alright, on to some specifics! First, I’d like to mention the new TR1 tuple and array classes. Then I’ll talk just a bit about shared_ptr. I’ll finish up with some information about regex, TR1’s regular expression utility. Again, people who are familiar with TR1 probably won’t get much out of this, but it will hopefully whet the appetite of those who are new to TR1.

Tuple is very much like the existing pair class, except that it can hold up to ten items instead of just two. Just like you can have pair<INT, char> p;, you can have something like tuple<INT, char, int, double, char*> t;. Handy, no?

TR1’s array class is very much like a fixed-length STL vector. Vector is a very useful class, and it is probably sufficient (even preferable) for most array-type needs. However, there are some situations where the developer is absolutely positive that the array needed will always be a particular size… no more, no less. In these cases, the variable-size feature of vector is not needed and just adds extra overhead. While you could just use a regular old C-style “square-bracket” array, the TR1 array class lets you use all of the STL-type iterators and algorithms. While it lacks some of the flexibility of a vector, it opens up more options than are available with a C-style array.

Shared_ptr is a very easy-to-use tool that greatly simplifies memory management. It all but makes new/delete combinations obsolete. Shared_ptr is a smart pointer class that is pretty easy to use. The syntax is fairly simple… shared_ptr<STRING> sp(new string(“foo”)); creates a shared_ptr called sp to a string containing “foo”. This shared_ptr will act almost just like any “normal” pointer, except that you don’t need to remember to delete it when you’re done. And unlike some older smart pointers, you don’t need to modify the target class (in this case, string) to include reference counting or anything like that… nearly any class you want will work with shared_ptr as-is. Speaking of reference counting, shared_ptr takes care of that (hence the “shared” in the name). If I were to make another shared_ptr that points to the same thing (like shared_ptr<STRING> sp2 = sp;), then shared_ptr’s reference counting is smart enough to only free up the memory when BOTH sp and sp2 are gone. Of course, this barely scratches the surface of what shared_ptr is all about, but it’s a start.

Regex is a class that lets you write complex regular expressions like those commonly used in Perl. While C++ has always had some amount of support for regular expressions, TR1’s regex utilities simplify things by building in the mechanics for parsing, matching, and capture groups. The regex class holds the actual regular expression, and algorithms such as regex_search(), regex_match(), and regex_replace() make it easy to apply that expression to a string. As you can probably deduce from the algorithm names, regex_search() tells the developer if the string contains any substrings that conform to the expression, regex_match() tells if the entire string conforms to the expression, and regex_replace() provides an easy way to change the string to fit a particular format. Regex can do quite a bit more than I’ve outlined here, but this should give you an idea of what regex is all about.

Well, that’s about all I wanted to say here. If any of this kindles some new interest in TR1 in any of the vcblog readers, great! Of course, any comments or questions that you might have will be appreciated.

Rob Huyett, VC Libraries Team

Posted in C++


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