C++ Advanced Features (TCF 2014)

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C++ Advanced
Features
Trenton Computer Festival
March 15, 2014
Michael P. Redlich
@mpredli
about.me/mpredli/
Sunday, March 16, 14

Who’s Mike?
• BS in CS from
• “Petrochemical Research Organization”
• Ai-Logix, Inc. (now AudioCodes)
• Amateur Computer Group of New Jersey
• Publications
• Presentations
2

Objectives
• Overloaded Operators
• Templates
• Exception Handling
• Namespaces
• Introduction to the Standard Template
Library (STL)
3

Overloaded Operators
4

What are Overloaded
Operators?
• Deﬁne basic operations for objects of user-
deﬁned types
• as if they were built-in types
• Often referred to as “syntactic sugar”
5

6
// String.h - a simple string class
class String {
private:
char *string;
public:
String(char const *str) {
string = new char[strlen(str) + 1];
strcpy(string,str);
}
~String(void) {
delete[] string;
}
char *getString(void) const {
return string;
}
};

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// main application
#include “String.h”
// create two different objects of type String
String string1 = “Hello, C++ Users Group!”;
String string2 = “Hello, Java Users Group!”;
// a conditional *without* an overloaded equality operator
if(strcmp(string1.getString(),string2.getString()) == 0)
// do this
else
// do that
// a conditional *with* an overloaded equality operator
if(string1 == string2)
// do this
else
// do that

(1)
• An overloaded operator has the form:
• T [class::]operatorω(paramList)
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(2)
•string1 == string2
• interpreted as
string1.operator==(string2);
• string1 is the object in control
• string2 is the argument passed into the
operator
9

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// Equality Operator
bool string::operator==(string const &s) {
return(strcmp(
getString(),s.getString()) == 0);
}

(3)
• Attractive, but can be dangerous!!
• deep vs. shallow copy
• assignment operator side effects
• The compiler automatically generates an
assignment operator if one is not explicitly
deﬁned
• memberwise assignments
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(4)
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“Hello, C++ Users Group!”
“Hello, Java Users Group!”
string1.string
string2.string

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// compiler-generated Assignment Operator
string &string::operator=(string const &s) {
string = s.string;
return *this;
}
// main application
string1 = string2;

(5)
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“Hello, C++ Users Group!”
string1.string
string2.string

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// user-defined Assignment Operator
string &string::operator=(string const &s) {
delete[] string;
string = new char[strlen(s) + 1];
strcpy(string,s);
return *this;
}
// application
string1 = string2;

(6)
16
string1.string
string2.string

(7)
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Operators Than Can Be OverloadedOperators Than Can Be OverloadedOperators Than Can Be OverloadedOperators Than Can Be OverloadedOperators Than Can Be OverloadedOperators Than Can Be OverloadedOperators Than Can Be OverloadedOperators Than Can Be OverloadedOperators Than Can Be OverloadedOperators Than Can Be Overloaded
+ - * / % ^ & | ~ !
= < > += -+ *= /= %= ^= &=
|= << >> >>= <<= != <= >= &&
|| ++ -- ‘ ->* -> () []
ne
w
de
le
te

(8)
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Operators That Cannot Be OverloadedOperators That Cannot Be OverloadedOperators That Cannot Be OverloadedOperators That Cannot Be Overloaded
. .* :: ?:

(9)
• Limitations:
• the meaning of an operator cannot be changed
• the number of operands for an operator cannot
be changed
• operator precedence and associativity cannot be
changed
• no personal operators!!
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Templates
20

What are Templates?
• Used for generic programming
• Two kinds:
• class templates
• member function templates
21

Templates (1)
• Prototypes:
• template <class T> returnType
functionName(paramList) {}
• template <class T> class
className {}
22

23
// swap member functions to handle different data types
void swap(int &first,int &second) {
int temp = second;
second = first;
first = temp;
}
void swap(float &first,float &second) {
float temp = second;
second = first;
first = temp;
}
void swap(char *&first,char *&second) {
char *temp = second;
second = first;
first = temp;
}

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/*
* function template to swap two elements
* of any data type
*/
template <class T>
void swap(T &first,T &second) {
T temp = second;
second = first;
first = temp;
}

Templates (2)
• A template specialization is the speciﬁc use
of a template member function or class
• swap<int>(1,2);
• swap<float>(1.7,3.5);
• swap<char>(‘a’,’b’);
• swap<char *>(“Mets”,”Jets”);
25

Exception Handling
26

What is Exception
Handling?
• A more robust method for handling errors
than fastidiously checking for error codes
• error code checking is tedious and can obscure
program logic
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Exception Handling (1)
• Throw Expression:
• raises the exception
• Try Block:
• contains a throw expression or a member
function that throws an exception
28

• Catch Clause(s):
• handles the exception
• deﬁned immediately after the try block
• multiple catch clauses allowed
• no implicit data type conversions
• catch(...) catches any exception type
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C++ Exception Model
• Destructors invoked for all live objects as
the stack “unwinds”
• Exception Speciﬁcation
• specify what type of exception(s) a member
function will throw
• Termination vs. Resumption semantics
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// exception handling example
#include <string>
#include <stdexcept>
void fred(void) {
FILE *file = fopen(“filename.txt”,”rt”);
try {
if(file == NULL) { // file could not be opened
throw 1;
}
int g = george(-1);
}
catch(int e) {
cout << “ERROR: Could not open file...” << endl;
}
catch(string const message) {
cout << message << endl;
}
// other statements...
}
// continued on next slide...

32
// continued from previous slide...
int george(int n) {
if(n < 0) {
string message = “ERROR: Value less than zero...”;
throw message;
}
return n;
}

C++ Exception Class
Hierarchy (1)
• exception
• logic_error (client program errors)
• runtime_error (external errors)
• bad_alloc (memory allocation errors)
33

C++ Exception Class
Hierarchy (2)
• exception
• bad_cast (dynamic casting errors)
• bad_exception (unexpected())
• bad_typeid (RTTI errors)
34

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// exception handling example (revised)
#include <string>
#include <stdexcept>
void fred(void) {
FILE *file = fopen(“filename.txt”,”rt”);
try {
if(file == NULL) { // file could not be opened
throw runtime_error(“ERROR: Could not open file...”);
}
int g = george(-1);
}
catch(runtime_error &re) {
cout << re.what() << endl;
}
catch(string const message) {
cout << message << endl;
}
}

• Do not throw exceptions:
• to indicate special return values
• in copy constructors and assignment operators
• stroustrup.com/3rd_safe.pdf
36

Namespaces
37

What are Namespaces?
• Used to prevent global naming conﬂicts
• All C++ standard library components are
contained within a single namespace called
std
38

39
// an example of using header files from different sources
// baseball.h
...
int strike = 0;
...
// bowling.h
...
bool strike = false;
...
// main application
#include baseball.h
#include bowling.h // ERROR: strike already declared

40
// an example of using header files from different sources
// baseball.h
namespace baseball {
...
int strike = 0;
...
}
// bowling.h
namespace bowling {
...
bool strike = false;
...
}
// main application
#include baseball.h
#include bowling.h // OK!

Namespaces (1)
• Fully-qualiﬁed member names:
• namespace name
• scope resolution operator (::)
• member name
• baseball::strike
• bowling::strike
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Aliases
• Provides shorthand for the fully-qualiﬁed
namespace name
• Has the form:
• namespace m = N;
• namespace bb = baseball;
• namespace bw = bowling;
42

Using Directive
• Provides access to all members of a
namespace without having to write the
fully-qualiﬁed namespace member names
• Has the form:
• using namespace N;
• using namespace baseball;
• using namespace bowling;
43

Using Declaration
• Provides access to individual members of a
namespace without having to write the
fully-qualiﬁed namespace member names
• Has the form:
• using N::m;
• using baseball::strike;
• using bowling::strike;
44

Standard Template
Library (STL)
45

What is the STL?
• A subset of Standard C++
• First developed by HP Labs in 1994
• Three main parts:
• containers
• iterators
• algorithms
46

What are Containers?
• A data structure that contains a sequence
of elements
• Sequential containers:
• organize elements linearly
• Sorted associative containers:
• organize elements based on a key
47

Containers (1)
• Primarily chosen by how well it can
perform certain operations, such as:
• add elements to the container
• remove elements from the container
• rearrange elements within the container
• inspect elements within the container
48

Containers (2)
49
vector deque list set/map
insert O(n) O(n) O(1) O(nlogn)
prepend O(n) O(1) O(1) O(nlogn)
ﬁnd O(n) O(n) O(n) O(nlogn)
X[i] O(1) O(1) O(n) O(n)
pointers 0 1 2 3

What are Iterators?
• A generalization of a C/C++ pointer
• Used to access elements within an ordered
sequence
• Considered the “glue” that tie together
containers and algorithms
50

Iterators
• Five types:
• input
• output
• forward
• bi-directional
• random access
51

52
#include <vector>
typedef vector<int>::iterator iterator
vector<int> v(10);
for(int i = 0;i < 9;++i) {
v.push_back(i);
}
iterator current = v.begin();
iterator last = v.end();
while(current != last) {
cout << *current << “n”;
++current;
}
0 1 2 3 4 5 6 7 8
current last

What are Algorithms?
• Perform various operations on containers
such as:
• searching
• sorting
• transforming
53

Algorithms
• Non-Mutating
• binary_search
• count
• equal
• find
• Mutating
• copy
• generate
• remove
• reverse
• sort
54

Popular C++
Compilers
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• Embarcadero C++ Builder XE5
• embarcadero.com/products/
cbuilder
• MicrosoftVisual C++
• microsoft.com
• Open Watcom 1.9
• openwatcom.org

Local C++ User
Groups
• ACGNJ C++ Users Group
• facilitated by Bruce Arnold
• acgnj.barnold.us
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Further Reading (1)
57
• C & C++ Code Capsules
• Chuck Allison
• freshsources.com
• The C++ Programming Language
• Bjarne Stroustrup
• stroustrup.com/4th.html

Further Reading (2)
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• The Annotated C++ Reference Manual
• Margaret Ellis and Bjarne Stroustrup
• stroustrup.com/arm.html
• 1997 C++ Public Review Document
• C++ ISO JTC1/SC22/WG21 Committee
• open-std.org/jtc1/sc22/open/
n2356

Upcoming Events (1)
• Trenton Computer Festival
• March 14-15, 2014
• tcf-nj.org
• Emerging Technologies for the Enterprise
• April 22-23, 2014
• phillyemergingtech.com
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Upcoming Events (2)

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Thanks!
mike@redlich.net
@mpredli
javasig.org

C++ Advanced Features (TCF 2014)

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