C++11: Range-based for-loops and auto

One of the downsides to using C++ in recent years has been how verbose it is compared to some other languages, such as Java, C#, or Scala, just to name a few. One of the goals of the new C++11 standard was to allow for code that is more terse, and I must say, I love it.

One of the things about using STL in C++ that has always bothered me was how bulky it is. Let's take for example, iterating over a vector of strings, using the standard C++03 for-loop.

std::vector<std::string> words;
words.push_back("Hello");
words.push_back("World");
words.push_back("...and good morning!");

std::vector<std::string>::const_iterator wordItr;
for (wordItr = words.begin(); wordItr != words.end(); ++wordItr)
{
    std::cout << (*wordItr).c_str() << " ";
}

That's a lot of code just to loop through the words and print each one. In C++11 they have introduced a new keyword: auto. auto assumes the type of whatever is assigned to it, making it less verbose when the type would be especially long, such as std::vector::const_iterator. Let's see if we can clean up the code a bit using the auto keyword.

std::vector<std::string> words;
words.push_back("Hello");
words.push_back("World");
words.push_back("...and good morning!");

for (auto word = words.cbegin(); word != words.cend(); ++word)
{
   std::cout << (*word).c_str() << " ";
}

That's a fair amount better. We didn't have to spend an entire line of code just creating our iterator variable, auto saved so much room we we able to do it inline within the for-loop. However, we still have to initialize to begin(), and compare against end(), and increment the iterator. Those things are so standardized, it would be great if the for loop could take care of that for us. And it can! C++11 introduces range-based for-loops to do just that.

std::vector<std::string> words;
words.push_back("Hello");
words.push_back("World");
words.push_back("...and good morning!");

for (auto word: words)
{
    std::cout << word.c_str() << " ";
}

auto takes care of the type for us so we don't have to type out the entire iterator, and the range-based for-loop takes care of the initialization, comparison, and incrementing of the variable. On top of that, the range-based for-loop takes care of giving us the value pointed to by the iterator itself, so we don't have to dereference the iterator to get the string it points to. This means instead of (*word).c_str() we can just do word.c_str().

Also, for those of you who use Visual Studio, the good news is that Visual Studio 11 will have support for range-based for-loops. It was reported in September that it would not have support for it, but after people complained for months about it, it looks like Microsoft decided to put some more work into their compiler. If you would like to try it out in Visual Studio the VS11 Beta is out and supports it: http://blogs.msdn.com/b/vcblog/archive/2012/02/29/10272778.aspx

I have noticed however that the IDE doesn't properly recognize it, and will give you warnings if you hover over parts of the for-loop, but it does compile and run. I'm sure this is something they'll have fixed in the final version. Regardless, VS11 does not support nearly as much of C++11 as other compilers like GCC, which are free, and I'm not sure I could restrict myself to a compiler that would restrict my learning and development as a programmer. But, I sure do love the IDE of Visual Studio, and I'm going to miss that.