Built-In (a.k.a. Native) Types in C++ .ppt

1、Built-In (a.k.a. Native) Types in C+,int, long, short, char (signed, integer division) unsigned versions too unsigned int, unsigned long, etc. C+ guarantees a char is one byte in size Sizes of other types are platform dependent Can determine using sizeof() , INT_MAX float, double (floating point div

2、ision) More expensive in space and time Useful when you need to describe continuous quantities bool type Logic type, takes on values true, false,User (& Library) DefinedTypes in C+,enumerations enum primary_color red, blue, yellow;functions and operators For example, things called from main function

3、structs and classes Similar abstractions in C+, extend C structs,Comparing C+ Classes and Structs,struct My_Data My_Data (int i) : x_(i) int x_; ;class My_Object public:My_Object ();My_Object ();private:int y_; ;,Struct members are public by default Class members are private by default Both can have

4、 Constructors Destructors Member variables Member functions Common practice: use structs for data use classes for objects with non-trivial methods,More About Both Native and User Types,Pointers raw memory address of an object or variable its type constrains what types it can point to (more later) ca

5、n take on a value of 0 (not pointing to anything) References “alias” for an object or variable its type constrains what types it can refer to (more later) cannot be 0 (always references something else) Mutable (default) vs. const types (read right to left) const int i; / read-only declaration int j;

6、 / readable and writable declaration,Scopes in C+,Each symbol is associated with a scope The entire program (global scope) A namespace (namespace scope) Members of a class (class scope) A function (function scope) A block (block scope)A symbol is only visible within its scope Helps hide unneeded det

7、ails (abstraction) Helps prevent symbol conflicts (encapsulation),Why Use Namespaces?,Classes encapsulate behavior (methods) and state (member data) behind an interface Structs are similar, but with state accessible Classes and structs are used to specify self-contained, cohesive abstractions Can sa

8、y what class/struct does in one sentence What if we want to describe more loosely related collections of state and behavior? Could use a class or struct But that dilutes their design intent,Namespaces,C+ offers an appropriate scoping mechanism for loosely related aggregates: Namespaces Good for larg

9、e function collections E.g., a set of related algorithms and function objects Good for general purpose collections E.g., program utilities, performance statistics, etc. Declarative region Where a variable/function can be declared Potential scope Where a variable/function can be used From where decla

10、red to end of declarative region,Namespace Properties,Declared/(re)opened with namespace keyword namespace Foo int baz_; namespace Foo int fxn() return baz_; Access members using scoping operator : std:cout “hello world!” std:endl; Everything not declared in another namespace is in the global (progr

11、am-wide) namespace Can nest namespace declarations namespace Foo namespace Err ,Using Namespaces,The using keyword makes elements visible Only applies to the current scope Can add entire namespace to current scope using namespace std; cout “hello, world!” endl; Can introduce elements selectively usi

12、ng std:cout; cout “hello, world!” std:endl; Can also declare unnamed namespaces Elements are visible after the declaration namespace int i_; / i_ is now visible ,C+ string Class,#include #include using namespace std; int main (int, char*) string s; / emptys = “”; / emptys = “hello”; s += “, ”;s = s

13、+ “world!”;cout s endl; / prints: hello, world!return 0; , header file Various constructors Assignment operator Overloaded operators += + = = The last one is really useful: indexes string if (s0 = h) ,Using C+ vs. C-style Strings,#include #include using namespace std; int main (int, char*) char * w

14、= “world”;string sw = “world”;char * h = “hello, ”;string sh = “hello, ”;cout (h w) endl; / 0: why?cout (sh sw) endl; / 1:why?h += w; / illegal: why?sh += sw;cout h endl;cout sh endl;return 0; ,C-style strings are contiguous arrays of char Often accessed through pointers to char (char *) C+ string c

15、lass (template) provides a rich set of overloaded operators Often C+ strings do “what you would expect” as a programmer Often C-style strings do “what you would expect” as a machine designer Suggestion: use C+ style strings any time you need to change, concatenate, etc.,C+ Input/Output Stream Classe

16、s,#include using namespace std; int main (int, char*) int i;/ cout = std ostreamcout i; cout “You said ” i “.” endl;return 0; , header file Use istream for input Use ostream for output Overloaded operators istream extraction operator Other methods ostream: write, put istream: get, eof, good, clear S

17、tream manipulators ostream: flush, endl, setwidth, setprecision, hex, boolalpha,C+ File I/O Stream Classes,#include using namespace std; int main () ifstream ifs;ifs.open (“in.txt”);ofstream ofs (“out.txt”);if (ifs.is_open (), header file Use ifstream for input Use ofstream for output Other methods

18、open, is_open, close getline seekg, seekp File modes in, out, ate, app, trunc, binary,C+ String Stream Classes,#include #include #include using namespace std; int main (int, char*) ifstream ifs (“in.txt”);if (ifs.is_open ()string line_1, word_1;getline (ifs, line_1);istringstream iss (line_1);iss wo

19、rd_1;cout word_1 endl;return 0; , header file Use istringstream for input Use ostringstream for output Useful for scanning input Get a line from file into string Wrap string in a stream Pull words off the stream Useful for formatting output Use string as format buffer Wrap string in a stream Push fo

20、rmatted values into stream Output formatted string to file,Using C+ String Stream Classes,#include #include #include using namespace std; int main (int argc, char *argv) if (argc f; argsin g;cout f “ / ” g “ is ” f/g endl;return 0; ,Program gets arguments as C-style strings But lets say we wanted to

21、 input floating point values from the command line Formatting is tedious and error-prone in C-style strings (sprintf etc.) iostream formatting is friendly Can we get there from here?,Storing Other Data Types Than char,There are many options to store non-char data in C+ Differ in complexity, ease of

22、useNative C-style arrays Can not add or remove positions Can index positions directly Not necessarily zero-terminated (why?)STL list container (bi-linked list) Add/remove positions on either end Cannot index positions directlySTL vector container (“back stack”) Can add/remove positions at the back C

23、an index positions directly,X,0,1,2,3,4,X,X,0,1,2,3,4,A Quick Look at Vectors,Goals Give you a good basic data structure to use for now Cover its correct usage Start understanding why Vectors: nicer than arrays Less to manage/remember Harder to get things wrong (but still need to be careful)Example

24、to the left prints v0 is 1 v1 is 2 v2 is 4,#include #include using namespace std; int main (int, char *) vector v;/ This would be asking for trouble/ v0 = 1; v1 = 2; v2 = 4;/ . but this works fine.v.push_back (1);v.push_back (2);v.push_back (4);/ . and now this is ok .for (size_t s = 0; s v.size(); +s) cout “v“ s “ is “ vs endl;return 0; ,