CSE 303 Concepts and Tools for Software Development Dan Grossman Spring 2005 Lecture 28 A Taste of C Wrap Up Dan Grossman CSE303 Spring 2005 Lecture 28 1 About the Final Next Tuesday this room 2 30 4 20 I think it s hard because it more explanation less fill in the blank than the midterm and a bit long Intended to test second half of the course but that includes plenty of C issues Does not cover C or html cgi Does cover debuggers profilers linking issues testing and assertions make version control manual memory management and concurrency Warning Though the homework has not used Java class has Dan Grossman CSE303 Spring 2005 Lecture 28 2 C An enormous language Used in some department classes many companies Hopefully knowing C and Java makes C easier to pick up All of C almost backwards compatible Some new keywords Compiled linked differently Like Java classes inheritance methods fields public vs private Still distinguishes objects and pointers to objects More OO features control multiple inheritance non virtual functions Other templates operator overloading reference parameters namespaces exceptions Dan Grossman CSE303 Spring 2005 Lecture 28 3 The C part struct and class names can be used as type names Functions taking different arguments can have the same name Compiler name mangles so that linking still works So you cannot just link C and C files together Either recompile the C as C or Call from C to C using extern C declaration Lots more libraries for convenient things like output and input really cleverly using C features namespaces either add using namespace std near the top of your file or prefix things e g std cout That way you can avoid name conflicts so long as namespaces do not reuse names very useful for large programs All the same ways to crash casts still not checked Dan Grossman CSE303 Spring 2005 Lecture 28 4 The Java part Not everything is in a class but you can define classes with fields methods constructors etc And you can call new to get a pointer to a heap allocated object initialized by calling the appropriate constructor To get Java style overriding you must declare the method virtual in the superclass Java has no notion of non virtual Other minor notes Can declare methods in the class definition e g in a header file and define them elsewhere e g in a cc file Actually structs and classes are the same thing except different defaults about public vs private No real need for static fields members because not everything needs to be in a class Dan Grossman CSE303 Spring 2005 Lecture 28 5 More OO No interfaces Instead the more powerful multiple inheritance A superclass with all abstract pure virtual methods is like an interface Multiple inheritance has thorny issues in definition and implementation see CSE341 There are different notions of casts C has numeric conversions and reinterpret the bits Java has numeric conversions compile time upcasts and run time checked downcasts C essentially has all of the above Destructors and delete opposite of constructors called right before the actually free of memory Java has finalizers much less control over when they are called Dan Grossman CSE303 Spring 2005 Lecture 28 6 Operator overloading In C and Java the language sets what types built in operators require takes ints or floats or in Java strings takes a function takes a pointer In C you can make any operator work for any type s by defining a special function that gets called when the operator is invoked Possible uses in rough decreasing order of accepted style Make arithmetic ops work on a new thing e g bignums Use function call syntax for objects with one method Automatic reference counting Things like lst for iteration Related copy constructors let you change the behavior of assignment Dan Grossman CSE303 Spring 2005 Lecture 28 7 Templates Classes functions etc can be parameterized by types and actually other things too More convenient than void and casts On the surface like Java 1 5 generics and ML polymorphism But fundamentally just automatic code duplication more name mangling Necessary because different instantiations of T may have different sizes see CSE401 Requires leaking implementations must put templatized method and function bodies in header files Instantiation can be any type not just class types The Standard Template Library provides lots of data structures but can be hard to use correctly and efficiently Dan Grossman CSE303 Spring 2005 Lecture 28 8 C Summary All the danger of C but convenience and flexibility of OO programming Virtual methods are what you are used to in Java Operator overloading can let almost any syntax do almost anything Templates allow automatic code duplication Putting it together std cout is just a global variable of type ostream Operator overloading defines how works for an ostream and a char an ostream and an int etc The operators do the printing and return the same ostream implicit parentheses takes care of the rest Dan Grossman CSE303 Spring 2005 Lecture 28 9 Course Summary A lot of comfort and de magicalizing 90 of you thought 90 of your classmates knew more of that practical stuff A lot of pragmatic application of computer science 1 There are concepts behind gdb but there s also value in knowing a couple handfuls of commands 2 The best computer scientists are not the folks who have the largest number of utilities options and features memorized But the best computer scientists also don t know the least And they re definitely not afraid to learn new ones Dan Grossman CSE303 Spring 2005 Lecture 28 10 Some concepts too We did not just pick up one strange set of rules after another Shell scripting is about automating program invocation C programming is about a lower level of computing where all data is just bits and pointers are explicit memory is managed manually Debuggers and profilers are about how to characterize and measure running programs Linking make etc are about how code is created and combined to make running programs Assertions and specifications are about assumptions and the robustness of larger programs HTML and CGI is about making programs public Dan Grossman CSE303 Spring 2005 Lecture 28 11 Societal implications And we talked about ethics too We talked about it like computer scientists Overly logical rational understanding limitations of technology and humans We should not be making all the decisions ourselves but we should be actively engaged in the process Dan Grossman CSE303 Spring 2005 Lecture 28 12 The Ultimate
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