This course is for experienced C programmers who want to program in C++. The examples and exercises require a basic understanding of algorithms and object-oriented software.
4.10 C++11 Standard
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Del curso dictado por University of California, Santa Cruz
C++ For C Programmers, Part B
76 calificaciones
De la lección
Monte Carlo Hex Program, Further advanced C++ Topics and Patterns
This module shows how to use Monte Carlo evaluation in complex games such as Hex and Go. This had led top championship level play in both these games. The module discusses C++ assertions and exceptions for error handling and the new C++ 11 feature static asserts. Finally, the last part of the module introduces the idea of “Design Pattern”, a feature of modern OO programming.
Conoce a los instructores
Ira PohlProfessor
Computer Science
So what else is going on in this standard.
Here are some of the things that are going on and
a few of these things we're going to also show you today and
it's just too big a group of things to we need two more courses
of this size at least to go into detail on how to use everything in the new standard.
But some of you have different needs and
this will give you some sense of where you could go, what you further need
to do to understand some of the new capabilities.
So there added critical libraries so I said there was lot of experimentation over
the last 10, 15 years with libraries such as Boost library.
And in that experimentation,
the general C++ community said, these things work really well.
Let's adopt them.
We have enough experience.
We know what we need.
And so, they put into the new standard, the tuple wiper.
I will show you an example later of tuples so we'll get to that.
There's a fixed length array container class, why a fixed length array?
Isn't vector just more flexible?
Vector is more flexible when it comes to the costs.
Remember, one of the principal reasons these libraries are so
widely adopted is because they're efficient.
Because they fit a critical need.
Sometimes the extra cost for
having a flexibility vector is not something you want to pay.
And you don't want to go to the primitive kind of array,
the pointer based array that C is.
You still would like nicer characteristics.
And that can be had through a template space, fixed length array here,
in which the length itself is a component of the type.
Double u link list.
That was the list in the original STL and now we're adding to it forward list.
Forward list is something which is cheaper because it doesn't require
a backward looking cursor, a backward pointer is only got a forward pointer so
it's single array link not a double array link.
Now here is something I think is of real value the unordered map and unordered set.
And we've already seen examples of that.
And the unordered versions of map and
set use hashing rather than log n based look up methods.
So we generally get a performance enhancement,
if we need that for associative arrays.
A big, big new addition is
threading libraries and other libraries such as atomic that mutex, that
let you do concurrent programming, threaded-base programming,
within a C++ standard rather than what was always allowed.
You could always use whatever your current library was.
For most people in Unix that might be
a p-thread library and that still might be the basis for this.
But now they've put into the standard at a little higher
level what the concurrency primitives need to be, and
then they let the implementation support that standard.
So now you can write more uniform code
across different platforms.
Another very valuable library is regular expression library.
This is probably one of the first libraries that people immediately wanted,
that wasn't in the standard, because regular expressions have been in
use in computer science and programming forever and they're just
an extremely useful way of parsing strings and so Just a natural addition.
And finally, among the interesting traditional
libraries is a type_traits library and
a type_traits library can be used also to use static assertions and
very helpful in writing more portable code and
code that can be statically checked after you instantiate a template so
that again is very important especially for
modern day generic programming.
So all of this stuff, and it's huge, I mean,
I'm just going to give you the barest roadmap through this stuff and
for your particular purposes you're going to have to go and study at length.
The good news is lots of material available in studying this.
Lots of material already on the web where you can read about any of this.
Okay, now the quiz question.
We've used an unordered_map before, so hash based lookup.
If there are no collisions and
you're using an unordered map instead of a map for n elements.
What is the order that the computation is going to take?
Voila, it is constant time.
And that means it's extremely efficient especially if there no collisions.
And that's going to be the normal case.
And this is typically preferred to an ordinary map because an ordinary
map is usually implemented with red black trees all the basic
operations there are logarithmic, as opposed to fixed-time.
So this is going to dominate where you need that performance.
Okay, let's take a look at one of these newer libraries.
Let's see how we can use the regular expression library.
So regular expressions, I don't know if you know your Chomsky hierarchy.
But regular expressions is sort of the lowest
level of formal language hierarchical rule writing.
Typically a regular expression is something like repeatedly
writing a series of a's and b's.
So any sequence of a's and b's can be expressed as a regular expression.
One up from a library expression, again, if you have some computer science
background, would be context free languages.
And they require more stringent rules, and they're more difficult to surpass.
So, regular expressions have very simple roles, but they encompass lots of
different languages, and they're very, very simple to parse.
And the regular expression package gives you a basis for expressing those rules.
So, here for example is a regular expression and
what its saying in this little thing here is any
sequence that uses lowercase characters is okay.
So that would mean a b x x
t u that's okay, but
a b x 3 t u not okay, why?
Because that's not in that alphabet.
So this bracketing thing says here are the characters I'm allowing,
the plus thing says you can repeat it as much as possible so
you can get into the alphabet and repeat it as much as possible and
then this last part says explicitly in the string I need .txt.
So this regular expression declared that way
would be an arbitrary set of lowercase letters,
followed by a period dot t this would match the example myfilename.txt.
And that would be okay.
Let's use it in a little piece of code.
So as with anything in the standard library,
we import the standard library, it's now called regex.
And it's typically used with strings, so
you'll almost always see string when you're seeing regex.
And here is series of strings.
So we have an array of strings, four element array initialized.
Ira.txt, data.txt, ira2.txt, a.out,
we have that expression and now we're going to say for
i=0 to 4, C print out the string and
then see if there's a match between the string and
the regular expression.
So here's the regular expression, here's the string this leads to
if there's a match you get one, there's no match, you get 0.
So think about what that should be doing for these four.
What will get printed there?
We have ira.txt, data.txt, ira2.txt, a.out,
all standard names, file names, and we're asking, which matches that?
Maybe, for the text files, of a certain kind, we want to do further processing.
So, that, again.
So, we want to differentiate,
in this way that again is one of the reasons this is so powerful.
Ira.txt is okay, series of lowercase letters and
then followed by the appropriate extension.
So this shows at the match is true but
ira2 is not okay, why is ira2 not okay?
2 not in [ a- z ] and
a.out is not okay
because .out not .txt.
Now, for those of you who are familiar with regular expressions,
you can go to that library and
see all the ways you can express different kinds of regular expressions,
say we don't have enough time to show the full support in library.
But once you understand the fundamental idea or
if you view regular expressions in other
circumstance with languages like Perl
is a heavily based regular expression
language or Unix utilities like awk.
This will be very familiar to you.
You'll be able to use it directly in the language.
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