Cours de C++ Utilisations des conteneurs

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1 Cours de C++ Utilisations des conteneurs Cécile Braunstein 1 / 18

2 Introduction Containers - Why? Help to solve messy problems Provide useful function and data structure Consistency between containers Containers Collection of objects Defined with the template classes : Seperate the containerfrom the type of the data inside. Each containers type is optimized for a specific use (access/modification). Main containers : list, vector, stack, queue, map 2 / 18

containers Containers Collection of objects Defined with the template classes : Seperate the

3 Example : vector Action Insert an element Remove an element Remove all elements Returns a value that denotes the first element Returns a value that denotes (one past) the last element Returns a value that denotes the i th element Take the vector size Check emptiness Method v.push_back() v.pop_back() v.clear() v.begin() v.end() v[i] v.size() v.empty() Attention : The first element is indexed by 0 and the last by size-1. 3 / 18

denotes the i th element Take the vector size Check emptiness Method v.push_back() v.pop_back() v.clear() v.

4 Container s type list Insert and remove anywhere in constant time Automatic memory management vector General purpose Fast access by index (constant time) Insert and remove an element at the end in constant time Other insert and remove in linear time set, map Access an element by a key in constant time Fast search of an element 4 / 18

remove an element at the end in constant time Other insert and remove in linear

5 Container s properties Containers have their own elements Elements of a container have to support the copy and assigment instruction (=) All containers have a method empty() and size() in constant time All containers have a method begin() and end() 5 / 18

instruction (=) All containers have a method empty() and size()

6 Containers constructors container<t> c; container<t> c(c2); container<t> c(n); container<t> c(n,t); container<t> c(b,e); Empty container Copy of c2 With n elements value-initialized according to T With n elements copies of t Copy of the elements an other container between [b,e) 6 / 18

container Copy of c2 With n elements value-initialized according to T

7 How to choose? What is the purpose? How we want ot access the element (randomly, in one order...) Which modification on the collection of data (add/remove elements, sort...) Programm performance Access time/ Modification time Time depends on the number of elements Types of times : linear, log, exponential... Memory usage... 7 / 18

..) Which modification on the collection of data (add/remove elements, sort.

8 How to access element? Iterator Purpose Pointer generalization Use for a sequential access to elements Optimisation regarding the container s type Iterator Definition An iterator is a value that Identifies a container and an element in the container Lets us examine the value stored in that element Provides operations for moving between elements in the container Restricts the available operations to correspond to what the container can handle efficently 8 / 18

container s type Iterator Definition An iterator is a value that Identifies a container and an element in the

9 First example vector<double> v; //v is full vector<double>::size_type i; for(i = 0; i!= v.size(); ++i) { cout << v[i] << endl; } vector<double> v; //v is full vector<double>::iterator iter; for(iter = v.begin(); iter!= v.end(); ++iter) { cout << *iter << endl; } 9 / 18

10 Iterator Most general types Every standard container defines two iterator types : container-type : :iterator container-type : :const_iterator Operations Comparison (, =...) Incrementation Dereference Every operations that modify the containers invalid the iterator 10 / 18

:const_iterator Operations Comparison (, =.

11 Associative containers Goal What happen if we want to find a given value into a sequential containers? Look at each element one by one Sort the container and use a fast search algorithm Both solutions are quite slow or need sophistical algorithm Alternative : using associative containers Arrange elements that depends on the value of the element Exploit the ordering to locate element quickly It contains more information : key 11 / 18

slow or need sophistical algorithm Alternative : using associative containers Arrange elements that depends

12 Associative Array map example < key, value > When we put this pair into the data structure, the key will be associate to this value until we delete the pair. Works as vector But Key doesn t need to be an integer ; it can be any value that we can compare in order to keep them ordered Unique key values Associative containers is self-ordering : our program must not change the order of elements 12 / 18

Works as vector But Key doesn t need to be an integer ; it can be any value that we can compare in

13 Using associative containers The class pair Simple data structure that holds to element : first and second Each element of map is a pair first : key ; second : the associated value Iterator For a map with a key of type K and a value of type T the associated pair is : pair<const K, T> Access the key and the value with an iterator is : map<char,value>::iterator ite; ite->first; ite->second; 13 / 18

with a key of type K and a value of type T the associated pair is : pair<const K, T> Access the key

14 Compare fonction How to compare keys? When built-in type or type with comparaison function : use the defined ones When no comparaison exists : programmer have to write one map<k,v> m; map<k,v,t_fpt> m(fpt); map<k,v,comp> m; Empty map with keys of type const K and value of type V Map with the comparaison function as pointer function fpt with the prototype T_fpt Map with a comparison object to be used for the ordering 14 / 18

programmer have to write one map<k,v> m; map<k,v,t_fpt> m(fpt); map<k,v,comp> m; Empty map with keys of

15 Main operations map<key,t> begin end empty size operator[] insert erase find lower_bound upper_bound declaration Return iterator to beginning Return iterator to end Test whether container is empty Return container size Access element Insert element Erase elements Get iterator to element Return iterator to lower bound Return iterator to upper bound 15 / 18

container is empty Return container size Access element Insert element Erase elements Get

16 Use of an associative container map<string,double> m; m["abie"] = 2.5; m["sarah"] = 6.8; m["michael"]= 7.5; m.insert(pair<string,double>("thomas",5.2)); map<string,double>::iterator it; for(map<string,double>::iterator it = m.begin(); it!= m.end(); ++it) { cout << it->first << "\t" << it-> second << endl; } 16 / 18

2)); map<string,double>::iterator it; for(map<string,double>::iterator it = m.

17 Use of an associative container-constructor 1/2 bool compare(const string& s1, const string& s2) { return s1.size() >= s2.size(); } int main() { bool(*fn_pt)(const string&,const string&) = compare; map<string,double,bool(*)(const string&, const string &)> m(fn_pt);... } 17 / 18

$size(); } int main() { bool(*fn_pt)(const string&,const string&) =$

18 Use of an associative container-constructor 2/2 struct classcomp { bool operator() (const string& s1, const string& s2) const {return s1.size() <= s2.size();} }; int main() { map<string,double,classcomp> m;... } 18 / 18

Why you shouldn't use set (and what you should use instead) Matt Austern

Why you shouldn't use set (and what you should use instead) Matt Austern Everything in the standard C++ library is there for a reason, but it isn't always obvious what that reason is. The standard isn't