C++: Overview and Features

Transcription

1 C++: Overview and Features Richard Newman Room CS Programming & Design, Introduction You have: used streams seen how classes are used seen some C++ code Today: good and bad points of C++ quick overview of minor changes (e.g. syntax) streams & strings the STL: containers, algorithms, etc Programming & Design,

2 What C++ isn t Pretty (see: Python, Ruby, even Delphi): bool prime(const unsigned int i) { if ((i<=0) ((i%2) == 0)) return false; if (i<=3) return true; unsigned int divisor = 3; while ((divisor*divisor) <= i) { if ((i % divisor) == 0) return false; else divisor += 2; } return true; } def prime(i): if i <= 0 or i % 2 == 0: return False if i <= 3: return True divisor = 3 while divisor**2 <= i: if i % divisor == 0: return False else: divisor += 2 return True Programming & Design, What C++ isn t, cont. Elegant (designed by committee and history) #ifndef MY_HEADER_H #define MY_HEADER_H #include myheader.h #endif Well-abstracted (see: scripting languages - you still push bytes around) Pure (OO: Smalltalk, Ruby; Functional: ML) Programming & Design,

3 What C++ is Improvement/evolution of C. Capable of functional programming, objectoriented programming, and procedural ( a better C ). Flexible, precisely because you can still push bytes around. Well-established and supported. A pretty good multi-tool Programming & Design, A Very Fast Overview of things I m not going to cover properly. Namespaces. No more worries about name clashes! Exceptions. Error handling done properly. try, catch, and throw statements. C++ casts. Syntax changes: declarations can now be anywhere functions must be prototyped functions can now be overloaded and inlined references - like pointers, only not really no void in empty parameter lists Programming & Design,

4 Things to make your life easier Streams. Enormously powerful, and you can now do this: cout << anint <<, << astring << anobject << endl; The Standard Template Library. Provides vector, string, and other very useful classes Programming & Design, STL Containers STL provides containers: these are generalised things to hold objects. Uses templates - write code once, use for multiple types. Vector of int, double, string, pointers Lots in the STL, with guaranteed performance characteristics. Better than writing your own! Programming & Design,

5 Advantages Swappable. Everything implements the same set of interfaces (iterators, find, push_back, etc.), so if a list would be faster, you can replace a vector with one with minimal changes. Fast. The STL is well-implemented and well-designed. Reusable. Everything is templated, so as long as you follow some rules you can write your own container that supports all of the STL algorithms (like sorting), or an algorithm that works on all containers. And of course, you can use a container to hold any type Good overview (unusual for Geocities sites!): Programming & Design, Containers Example #include<vector> #include<list> #include<map> #include<iostream> using namespace std; int main() { vector<int> myvector; map<int, string> mymap; mymap[9] = "Richard"; cout << mymap[9] << endl; // prints Richard list< vector<int>* > myveclist; myveclist.push_back(new vector<int>(10)); cout << myveclist.size() << endl; for(list< vector<int>* >::iterator it = myveclist.begin(); it!= myveclist.end(); it++) cout << " " << (*it)->size() << endl; return 0; // ahem... } Programming & Design,

6 String Very useful class. Can be initialised from all sorts of things: character array (char *), string, literal Can reassign without difficulty - dynamic. string a, b; a = Hello! ; b = Oi + a; cout << b << endl; // prints Oi Hello! Programming & Design, Vector Array declarations in C: int a[5]; fixed length, or manual malloc. messy and difficult! STL vector: vector<int> a; // declares a vector of int cout << a.size(); // prints 0 - the size. // let s add two elements... a.push_back(5); a.push_back(10); cout << a[1]; // prints Programming & Design,

7 Vector Multidimensional vector: vector< vector<int> > a; Access through index: a[1][2] = 5; a[2].push_back(5); You ll probably never need to use a C array again. The STL similarly provides linked list (list), associative containers (map, hash_map), and everything else Programming & Design, Iterators Containers provide iterators over their elements. C: for(int i=0; i<arraylength;i++) { printf( %d\n, array[i]); } // prints contents of an array C++: for(map<int, string>::iterator it=mymap.begin(); it!=mymap.end(); it++) { cout << it->second << endl; } // prints out all of the strings in the map Difference: these work for dictionaries, sets Programming & Design,

8 Summary The main differences between C and C++ you ll notice on a daily basis are: strings, which are now safe and easy to work with vectors, which are now safe and dynamic streams, which make writing to files and the console easy for a variety of types the STL s algorithms and iterators, which mean you don t have so much to write to get something done objects, which allow a higher level of abstraction Programming & Design, Only a small part of your course, so of course there s no book. However, if you re going to be programming in C++ at all, I d recommend as a reference: Link ( 35) Book Programming & Design,

9 Assignment When doing the assignment, notice the facilities C++ offers to reduce the amount of work you do and improve the quality and safety of your programs. However: C++ is not the best language! It s a tool for solving problems Programming & Design, Solution Some of you won t have a good design (or one at all!) Some of you will have one that you won t have time to implement. This will save you! Programming & Design,

10 Classes BankAccount SavingsAccount CurrentAccount ISA See class diagram Programming & Design, Programming & Design,