Overview, C++ lecture 4. Topics for today: Standard Template Library Connecting Python and C++

Overview, C++ lecture 4

Topics for today:

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Standard Template Library

Example from STL: vector

#include <vector>

#include <iostream>

using namespace std;

int main() {

vector<int> vNumbers; vNumbers.push_back(1); cout << vNumbers[0]; return 0;

vector

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Similar to an ordinary C array, but dynamic, i.e.

the length can both increase and decrease.

Commonly used vector

functions

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[] - get/set, with bound checking in MSVC

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at - get/set, with bound checking

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push_back - appending objects

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capacity - the allocated nr of elem.

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reserve - request a capacity change

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clear - clear the content

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front - the first element

Standard Template Library

(STL)

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Originally created by Silicon Graphics

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Became a part of the C++ in 1994

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Many different implementations appeared

since then.

Common STL templates

Sequence containers Function

vector Dynamic array, one open end deque Dynamic array, two open ends list Doubly linked list

Container adaptors Function

stack LIFO (Last In - First Out) queue FIFO (First In – First Out) priority_queue Priority queue

Associative containers Function

set Mathematical set

STL collection functions

Function Returns

empty True if empty

size Number of elements

begin Forward iterator set to the first element

end Forward iterator set just past the last element rbegin Backward iterator set to the last element

rend Backward iterator set just before the first element clear Erases all elements, by calling all destructors and

setting the size tozero.

Queue example

#include <queue> queue<int> myQueue; myQueue.push(1); myQueue.push(7); myQueue.push(4);

while (!myQueue.empty()) {

cout << myQueue.front() << endl; myQueue.pop(); } ●

Output:

Priority queue example

#include <queue>

priority_queue<Task> prioQueue;

prioQueue.push(Task(4, "Go to the cinema"));

prioQueue.push(Task(9, "Solve the programming assignments"));

while (!prioQueue.empty()) {

cout << prioQueue.top().task << endl; prioQueue.pop();

}

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Output:

Solve the programming assignments Go to the cinema

Task class definition

class Task {

public:

Task(int _priority, string _task); bool operator<(const Task&) const; int priority;

string task; };

// The constructor

Task::Task(int _priority, string _task) : priority(_priority),

task(_task) {

};

// The comparison function

bool Task::operator<(const Task& right) const {

return priority < right.priority; }

set example

#include <set> set <int> mySet; mySet.insert(4); mySet.insert(2); mySet.insert(4);

for ( set<int>::iterator it = mySet.begin(); it != mySet.end();

it++ ) {

cout << *it << endl; }

// With BOOST_FOREACH defined as foreach, // the loop header could have been written: // foreach(int& val, mySet)

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Output:

map

#include <map>

map <int, double> myMap; myMap[1] = 4.7;

myMap[3] = 8.5; myMap[4] = 9.0;

// Accessing the data using a key

cout << "myMap[4] = " << myMap[4] << endl;

// Traversing all elements

for ( map<int,double>::iterator it = myMap.begin(); it != myMap.end();

it++) {

cout << it->first << " " << it->second << endl; }

// BOOST_FOREACH runs into trouble here

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Output:

myMap[4] = 9 1 4.7

3 8.5 4 9

Looping over a vector

using namespace std;

// Create a vector with two elements

vector<int> vec; vec.push_back(1); vec.push_back(2);

// Print the vector using an iterator

vector<int>::iterator it; for( it = vec.begin(); it != vec.end(); it++ ) { cout << *it << ” ”; }

Loop in latest C++ version

vector<int> vec;

vec.push_back( 10 ); vec.push_back( 20 ); for (int i : vec ) {

cout << i; }

Traversing using index

variable

using namespace std;

// Create a vector with two elements

vector<int> vIntegers; vIntegers.push_back(1); vIntegers.push_back(2);

for(int i=0; i<myIntVector.size(); i++)

{

cout << vIntegers[i] << " "; }

Sequence operations

vector<int> v1; vector<int> v2;

// Create some elements

for (int i=0; i<10; i++) v1.push_back(i);

random_shuffle(v1.begin(), v1.end()); v2 = v1;

sort(v2.begin(), v2.end());

// Print the vectors

// Assuming that BOOST_FOREACH is available and remapped to foreach

foreach(int val, v1) cout << val << " "; cout << endl; foreach(int val, v2) cout << val << " "; ●

Example output:

Connecting Python and C

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Using C-functions from Python: Wrapper

functions in C must be created

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Boost.Python or SWIG simplifies this process.

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Help on using SWIG:

Source file

//func.cpp

// Just contains a simple test function

int add(int a, int b) {

return a+b; }

SWIG interface file

//func.i

%module func %{

extern int add(int, int); %}

Compiling for use in Python

$ gcc -c -fpic func.c

● Create the wrapper code from the specification i func.i. Generates

func_wrap.c and func.py: $ swig -python func.i

● Compile the wrapper:

$ gcc -c -fpic func_wrap.c -I/usr/include/python2.4

● Link the object files to _func.so:

Use in Python

rontok> python

Python 2.3.5 (#2, Feb 23 2005, 18:16:39) [C] on sunos5

Type "help", "copyright", "credits" or "license" for more information.

>>> import func >>> func.add(2,7) 9

SWIG in Windows

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Swigwin together with Microsoft Visual C++.

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http://www.swig.org/download.html

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Look at the examples for Python which comes

STL material

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http://en.wikipedia.org/wiki/Standard_Template_Library

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http://www.cplusplus.com/reference/stl/