The Standard Template Library – part 2

auto_ptr<> Regular pointers may cause memory leaks Regular pointers may cause memory leaks void f() { SomeClass *ptr = new SomeClass; SomeClass *ptr = new SomeClass; … // exception or improperly implemented early return from f() // exception or improperly implemented early return from f() … delete ptr; // memory leak if this statement is not reached delete ptr; // memory leak if this statement is not reached} The memory leak may be avoided The memory leak may be avoided We may use exception mechanism to catch exceptions We may use exception mechanism to catch exceptions We shoud delete all allocated memory in case of early return We shoud delete all allocated memory in case of early return

auto_ptr<> auto_ptr is an object (template) that auto_ptr is an object (template) that Acts as an inteligent pointer Acts as an inteligent pointer Owns data assigned to it Owns data assigned to it Manages asigned data to avoid memory leaks Manages asigned data to avoid memory leaks (defined in header) (defined in header) void f() { std::auto_ptr ptr(SomeClass); std::auto_ptr ptr(SomeClass); … // exception or early return from f() – ok! // exception or early return from f() – ok! … // no need to delete ptr; ~auto_ptr() does it for us // no need to delete ptr; ~auto_ptr() does it for us}

auto_ptr<> auto_ptr owns data assigned to it auto_ptr owns data assigned to it Assignment from regular pointer not allowed Assignment from regular pointer not allowed // std::auto_ptr ptr = new SomeClass; ERROR, but there is a reset() There may be only one one auto_ptr that owns specific object/variable There may be only one one auto_ptr that owns specific object/variable copy constructor and assignment operator move data from source auto_ptr, so they modify their arguments – unusual behaviour copy constructor and assignment operator move data from source auto_ptr, so they modify their arguments – unusual behaviour auto_ptr should not be an element of a container (why?) auto_ptr should not be an element of a container (why?) auto_ptr acts as an inteligent pointer auto_ptr acts as an inteligent pointer Overloads *(ptr) and ptr-> Overloads *(ptr) and ptr-> It is a pointer to single object, not to an array, container – ok. It is a pointer to single object, not to an array, container – ok. Does not overload pointer arithmetic operators (++, [], etc) Does not overload pointer arithmetic operators (++, [], etc) Extra methods : Extra methods : T* get() – returns address of the owned data (or NULL), not changing ownership T* get() – returns address of the owned data (or NULL), not changing ownership T* release() – returns address of the owned data (or NULL), releasing ownership T* release() – returns address of the owned data (or NULL), releasing ownership void reset(T * ptr=0) – assignment from regular pointer, creating ownership void reset(T * ptr=0) – assignment from regular pointer, creating ownership

auto_ptr<> copy constructor copy constructor std::auto_ptr ptr1(SomeClass); std::auto_ptr ptr2(ptr1); // now ptr1 is empty assignment operator assignment operator std::auto_ptr ptr1(SomeClass); std::auto_ptr ptr2(SomeClass); ptr2=ptr1; // *ptr2 (old one) gets destructed first, // now ptr1 is empty

auto_ptr<> auto_ptr as argument or return value auto_ptr as argument or return value Should be passed as variable, not as reference Should be passed as variable, not as reference This way we create sink (argument) or source (ret. val.) of data This way we create sink (argument) or source (ret. val.) of data const auto_ptr const auto_ptr will not allow to transfer owned data to another auto_ptr will not allow to transfer owned data to another auto_ptr will not allow to assign data owned by another auto_ptr will not allow to assign data owned by another auto_ptr ultimately will destruct owned data ultimately will destruct owned data changing owned data still ok. changing owned data still ok. good for sink good for sink const auto_ptr & const auto_ptr & for functions operating on owned data without changing ownership for functions operating on owned data without changing ownership examples: util/autoptr1.cpp util/autoptr2.cpp examples: util/autoptr1.cpp util/autoptr2.cpp

auto_ptr<> auto_ptr as a member variable auto_ptr as a member variable may make destructor not necessary may make destructor not necessary is safe even for exceptions thrown by a constructor is safe even for exceptions thrown by a constructor as opposed to regular pointers, since if constructor fails then destructor is not executed as opposed to regular pointers, since if constructor fails then destructor is not executed usually requires implementing copy constructor and assignment operator usually requires implementing copy constructor and assignment operator since default ones woud remove data from object being assigned since default ones woud remove data from object being assigned

numeric_limits<> numeric_limits<> is a template that defines various properties of a numerical types numeric_limits<> is a template that defines various properties of a numerical types member variables and methods should be used to determine type properties at the compile time member variables and methods should be used to determine type properties at the compile time numeric_limits ::digits // no. of bits for integer types numeric_limits ::digits // no. of bits for integer types numeric_limits ::max() // easy to guess numeric_limits ::max() // easy to guess … it is implemented as a template that has specializations for all fundamental types it is implemented as a template that has specializations for all fundamental types

Special containers stack (LIFO queue, implemented using deque) stack (LIFO queue, implemented using deque) queue (FIFO queue, implemented using deque) queue (FIFO queue, implemented using deque) priority_queue priority_queue bitset bitset hash_set, hash_multiset, hash_map, hash_multimap hash_set, hash_multiset, hash_map, hash_multimap (implemented using hash table instead of binary tree)

stack header header simple LIFO queue implemented using deque simple LIFO queue implemented using deque may be based on any container supporting: back(), push_back(), pop_back(), may be based on any container supporting: back(), push_back(), pop_back(), just give 2 nd template argument, eg.: stack > just give 2 nd template argument, eg.: stack > just redirects own methods to deque methods to obtain LIFO queue just redirects own methods to deque methods to obtain LIFO queue example: cont/stack1.cpp example: cont/stack1.cpp push() push() pop() pop() top() // get the value of topmost element // but do not remove it from stack top() // get the value of topmost element // but do not remove it from stack size()// get the current number of elemets size()// get the current number of elemets empty()// is it empty empty()// is it empty operators: ==, !=,, =// == returns 1 if size and all elements are equal operators: ==, !=,, =// == returns 1 if size and all elements are equal no more methods or operators no more methods or operators

queue header header simple FIFO queue implemented using deque simple FIFO queue implemented using deque may be based on any container supporting: front(), back(), push_back(), pop_front() may be based on any container supporting: front(), back(), push_back(), pop_front() just give 2 nd template argument, eg.: queue > just give 2 nd template argument, eg.: queue > just redirects own methods to deque methods to obtain FIFO queue just redirects own methods to deque methods to obtain FIFO queue example: cont/queue1.cpp example: cont/queue1.cpp push() push() pop() pop() back() // get the value of element most recently push-ed // but do not remove it from stack back() // get the value of element most recently push-ed // but do not remove it from stack front() // get the value of element at the front of queue // but do not remove it from queue front() // get the value of element at the front of queue // but do not remove it from queue size()// get the current number of elemets size()// get the current number of elemets empty()// is it empty empty()// is it empty operators: ==, !=,, =// == returns 1 if size and all elements are equal operators: ==, !=,, =// == returns 1 if size and all elements are equal no more methods or operators no more methods or operators

priority_queue header header simple priority queue implemented using vector simple priority queue implemented using vector may be based on any container supporting: front(), push_back(), pop_front(), oper.[] may be based on any container supporting: front(), push_back(), pop_front(), oper.[] just give 2 nd template argument, eg.: priority_queue > just give 2 nd template argument, eg.: priority_queue > the 3 rd argument is a sort criterion (defaults to operator< ) the 3 rd argument is a sort criterion (defaults to operator< ) priority_queue, greater > redirects own methods to vector methods redirects own methods to vector methods example: cont/pqueue1.cpp example: cont/pqueue1.cpp push() push() pop() pop() top() // get the value of element of the greatest priority // but do not remove it from queue top() // get the value of element of the greatest priority // but do not remove it from queue size()// get the current number of elemets size()// get the current number of elemets empty()// is it empty empty()// is it empty no more methods or operators (no operator ==, etc.) no more methods or operators (no operator ==, etc.)

bitset header header convinient class for handling fixed size sets of bits convinient class for handling fixed size sets of bits bitset flags; performing bit stream i/o performing bit stream i/o example: cont/bitset1.cpp example: cont/bitset1.cpp also to perform integer i/o in binary format also to perform integer i/o in binary format example: cont/bitset2.cpp example: cont/bitset2.cpp no copy constructor or assignment operator no copy constructor or assignment operator

bitset bitset constructors bitset constructorsbitset<bits>::bitset() bitset ::bitset(unsigned long val) bitset ::bitset(const string &sc) // no char* initialization, couple variants of string initialization bitset methods and operators bitset methods and operators size() // return size of bitset count() // count ones any() // 1 if at least one bit set none() // !any() test(size_t idx) // is the idx-th bit set operator==(const bitset & arg) operator!=(const bitset & arg) …

bitset bitset methods and operators bitset methods and operators set() // set all to ones set(size_t idx, int value=1) reset() // set all to zeroes reset(size_t idx)// set idx-th to zeroes flip() // negate all bits flip(size_t idx) bitwise operators (argument size must match): ^= |= &= ^ | & ~ bitwise shift operators (size_t argument): >= >> steram operators: > bool operator[] (size_t idx) const // undefined behaviour if idx out of range bitset ::reference operator[] (size_t idx) // returns object of special proxy type // with reference type we may: =(bool), =(const reference &), flip(), operator~(), bool() to_ulong(), to_string()