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C++ Programming Code Examples

C++ > Code Snippets Code Examples

Find and display sorted v in lowest 20th percentile

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/* Find and display sorted v in lowest 20th percentile */ #include <algorithm> #include <iostream> #include <iterator> #include <vector> using namespace std; int main( ) { const int a[] = { 8, 7, 4, 9, 5, 2, 6, 2, 7,9, }; const int len = sizeof( a ) / sizeof( a[0] ); const int percentile_20 = static_cast<int>( 0.2 * len ); vector<int> v( a, a+len ); copy( a, a+len, v.begin() ); partial_sort( v.begin(), v.begin()+percentile_20,v.end() ); copy( v.begin(), v.begin()+percentile_20,ostream_iterator<int>( cout, " " ) ); }
Casting Operators in C++
A cast is a special operator that forces one data type to be converted into another. As an operator, a cast is unary and has the same precedence as any other unary operator. Converting an expression of a given type into another type is known as type-casting. The most general cast supported by most of the C++ compilers is as follows:
(type) expression
Where type is the desired data type. There are other casting operators supported by C++, they are listed below: • const_cast<type> (expr): The const_cast operator is used to explicitly override const and/or volatile in a cast. The target type must be the same as the source type except for the alteration of its const or volatile attributes. This type of casting manipulates the const attribute of the passed object, either to be set or removed. • dynamic_cast<type> (expr): The dynamic_cast performs a runtime cast that verifies the validity of the cast. If the cast cannot be made, the cast fails and the expression evaluates to null. A dynamic_cast performs casts on polymorphic types and can cast a A* pointer into a B* pointer only if the object being pointed to actually is a B object. • reinterpret_cast<type> (expr): The reinterpret_cast operator changes a pointer to any other type of pointer. It also allows casting from pointer to an integer type and vice versa. • static_cast<type> (expr): The static_cast operator performs a nonpolymorphic cast. For example, it can be used to cast a base class pointer into a derived class pointer. All of the above-mentioned casting operators will be used while working with classes and objects. For now, try the following example to understand a simple cast operators available in C++. Copy and paste the following C++ program in test.cpp file and compile and run this program.
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/* Type casting of the variables in the C++ programming language. Type casting refers to the conversion of one data type to another in a program. Typecasting can be done in two ways: automatically by the compiler and manually by the programmer or user. Type Casting is also known as Type Conversion. */ /* code example to demonstrate the casting of one variable to another using the implicit type casting in C++. */ #include <iostream> using namespace std; int main () { short x = 200; int y; y = x; cout << " Implicit Type Casting " << endl; cout << " The value of x: " << x << endl; cout << " The value of y: " << y << endl; int num = 20; char ch = 'a'; int res = 20 + 'a'; cout << " Type casting char to int data type ('a' to 20): " << res << endl; float val = num + 'A'; cout << " Type casting from int data to float type: " << val << endl; return 0; }
Iterator Library ostream_iterator in C++
Ostream iterators are output iterators that write sequentially to an output stream (such as cout). They are constructed from a basic_ostream object, to which they become associated, so that whenever an assignment operator (=) is used on the ostream_iterator (dereferenced or not) it inserts a new element into the stream. Optionally, a delimiter can be specified on construction. This delimiter is written to the stream after each element is inserted.
Syntax for Iterator ostream_iterator in C++
#include <iterator> template <class T, class charT=char, class traits=char_traits<charT> > class ostream_iterator;
T
Element type for the iterator: The type of elements inserted into the stream
charT
First template parameter of the associated basic_ostream object: The type of elements the stream handles (char for ostream).
traits
Second template parameter of the associated basic_ostream: Character traits for the elements the stream handles. The default template arguments correspond to an instantiation that uses an ostream object as associated stream.
Member types
Member types & definition in istream_iterator ostream_type: basic_ostream<charT,traits> --- Type of the associated output stream iterator_category: output_iterator_tag --- Input iterator value_type: void char_type: charT --- Type of the characters handled by the associated stream traits_type: traits --- Character traits for associated stream difference_type: void pointer: void reference: void
Member functions
• (constructor) Construct ostream iterator (public member function ) • operator* Dereference iterator (public member function ) • operator++ Increment iterator (public member function ) • operator= Assignment operator (public member function )
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/* C++ ostream_iterator is a special output iterator that write sequentially to an output stream. */ /* ostream_iterator class template - Output iterator to write items to an ostream */ /* C++ code example to illustrate read a bunch of strings from a file sort them lexicographically and print them to output stream */ #include <algorithm> #include <fstream> #include <iostream> #include <iterator> #include <string> #include <vector> using namespace std; int main() { // Define a vector to store the strings received from input vector<string> strings_v; // Define the filestream object used to read data from file ifstream fin("input_file.txt"); // Get input stream and end of stream iterators istream_iterator<string> fin_it(fin); istream_iterator<string> eos; // Get output stream iterators ostream_iterator<string> cout_it(cout, " "); // Copy elements from input to vector using copy function copy(fin_it, eos, back_inserter(strings_v)); // Sort the vector sort(strings_v.begin(), strings_v.end()); // Copy elements from vector to output copy(strings_v.begin(), strings_v.end(), cout_it); return 0; }
Namespaces in C++ Language
Consider a situation, when we have two persons with the same name, jhon, in the same class. Whenever we need to differentiate them definitely we would have to use some additional information along with their name, like either the area, if they live in different area or their mother's or father's name, etc. Same situation can arise in your C++ applications. For example, you might be writing some code that has a function called xyz() and there is another library available which is also having same function xyz(). Now the compiler has no way of knowing which version of xyz() function you are referring to within your code. A namespace is designed to overcome this difficulty and is used as additional information to differentiate similar functions, classes, variables etc. with the same name available in different libraries. Using namespace, you can define the context in which names are defined. In essence, a namespace defines a scope.
Defining a Namespace
A namespace definition begins with the keyword namespace followed by the namespace name as follows:
namespace namespace_name { // code declarations }
To call the namespace-enabled version of either function or variable, prepend (::) the namespace name as follows:
name::code; // code could be variable or function.
Using Directive
You can also avoid prepending of namespaces with the using namespace directive. This directive tells the compiler that the subsequent code is making use of names in the specified namespace.
Discontiguous Namespaces
A namespace can be defined in several parts and so a namespace is made up of the sum of its separately defined parts. The separate parts of a namespace can be spread over multiple files. So, if one part of the namespace requires a name defined in another file, that name must still be declared. Writing a following namespace definition either defines a new namespace or adds new elements to an existing one:
namespace namespace_name { // code declarations }
Nested Namespaces
Namespaces can be nested where you can define one namespace inside another name space as follows:
namespace namespace_name1 { // code declarations namespace namespace_name2 { // code declarations } }
• Namespace is a feature added in C++ and not present in C. • A namespace is a declarative region that provides a scope to the identifiers (names of the types, function, variables etc) inside it. • Multiple namespace blocks with the same name are allowed. All declarations within those blocks are declared in the named scope. • Namespace declarations appear only at global scope. • Namespace declarations can be nested within another namespace. • Namespace declarations don't have access specifiers. (Public or private) • No need to give semicolon after the closing brace of definition of namespace. • We can split the definition of namespace over several units.
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/* namespaces in C++ language */ // A C++ code to demonstrate that we can define // methods outside namespace. #include <iostream> using namespace std; // Creating a namespace namespace ns { void display(); class happy { public: void display(); }; } // Defining methods of namespace void ns::happy::display() { cout << "ns::happy::display()\n"; } void ns::display() { cout << "ns::display()\n"; } // Driver code int main() { ns::happy obj; ns::display(); obj.display(); return 0; }
Static Casting in C++
Static Cast: This is the simplest type of cast which can be used. It is a compile time cast.It does things like implicit conversions between types (such as int to float, or pointer to void*), and it can also call explicit conversion functions (or implicit ones). The static_cast is used for the normal/ordinary type conversion. This is also the cast responsible for implicit type coercion and can also be called explicitly. You should use it in cases like converting float to int, char to int, etc. This can cast related type classes. If you want to perform any type of conversion that is based on compile-time (static) inference, this is the way to go. We can do the common C-type casting using static_cast(), such as converting an int to a float, and vice-versa. Similarly, we can also convert between pointers and references.
new_type value = static_cast <new_type> (expression);
This will return a value of type new_type, after casting expression.
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/* A Cast operator is an unary operator which forces one data type to be converted into another data type. */ /* static_cast converts between types using a combination of implicit and user-defined conversions. */ #include <iostream> #include <string> using namespace std; class Int { int x; public: Int(int x_in = 0) : x{ x_in } { cout << "Conversion Ctor called" << endl; } operator string() { cout << "Conversion Operator" << endl; return to_string(x); } }; int main() { Int obj(3); string str = obj; obj = 20; string str2 = static_cast<string>(obj); obj = static_cast<Int>(30); return 0; }
Algorithm Library partial_sort() Function in C++
Partially sort elements in range. Rearranges the elements in the range [first,last), in such a way that the elements before middle are the smallest elements in the entire range and are sorted in ascending order, while the remaining elements are left without any specific order. The partial_sort() function is used for sorting a part of the range, not the entire range. It is present in the <algorithm> library. The elements are compared using operator< for the first version, and comp for the second.
Syntax for Algorithm partial_sort() Function in C++
#include <algorithm> //default (1) template <class RandomAccessIterator> void partial_sort (RandomAccessIterator first, RandomAccessIterator middle, RandomAccessIterator last); //custom (2) template <class RandomAccessIterator, class Compare> void partial_sort (RandomAccessIterator first, RandomAccessIterator middle, RandomAccessIterator last, Compare comp);
first, last
Random-access iterators to the initial and final positions of the sequence to be partially sorted. The range used is [first,last), which contains all the elements between first and last, including the element pointed by first but not the element pointed by last. Notice that in this function these are not consecutive parameters, but the first and the third.
middle
Random-access iterator pointing to the element within the range [first,last) that is used as the upper boundary of the elements that are fully sorted.
comp
Binary function that accepts two elements in the range as arguments, and returns a value convertible to bool. The value returned indicates whether the element passed as first argument is considered to go before the second in the specific strict weak ordering it defines. The function shall not modify any of its arguments. This can either be a function pointer or a function object. RandomAccessIterator shall point to a type for which swap is properly defined and which is both move-constructible and move-assignable. This function does not return any value.
Complexity
On average, less than linearithmic in the distance between first and last: Performs approximately N*log(M) comparisons of elements (where N is this distance, and M is the distance between first and middle). It also performs up to that many element swaps (or moves).
Data races
The objects in the range [first,last) are modified.
Exceptions
Throws if any of the element comparisons, the element swaps (or moves) or the operations on iterators throws. Note that invalid arguments cause undefined behavior.
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/* C++ Algorithm partial_sort() function is used to rearrange the elements in the range[first, last), in such a way that the elements between the first and middle will be sorted and the elements between the middle and last will be in an unspecified order. */ /* Partially sort elements in range by partial_sort() code example */ #include <iostream> #include <algorithm> #include <vector> using namespace std; // Defining the BinaryFunction bool comp(int a, int b) { return (a < b); } int main() { vector<int> v = { 1, 3, 1, 10, 3, 3, 7, 7, 8 }, i; vector<int>::iterator ip; // Using std::partial_sort std::partial_sort(v.begin(), v.begin() + 3, v.end(), comp); // Displaying the vector after applying // std::partial_sort for (ip = v.begin(); ip != v.end(); ++ip) { cout << *ip << " "; } return 0; }
#include Directive in C++
#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program.
Syntax for #include Directive in C++
#include "user-defined_file"
Including using " ": When using the double quotes(" "), the preprocessor access the current directory in which the source "header_file" is located. This type is mainly used to access any header files of the user's program or user-defined files.
#include <header_file>
Including using <>: While importing file using angular brackets(<>), the the preprocessor uses a predetermined directory path to access the file. It is mainly used to access system header files located in the standard system directories. Header File or Standard files: This is a file which contains C/C++ function declarations and macro definitions to be shared between several source files. Functions like the printf(), scanf(), cout, cin and various other input-output or other standard functions are contained within different header files. So to utilise those functions, the users need to import a few header files which define the required functions. User-defined files: These files resembles the header files, except for the fact that they are written and defined by the user itself. This saves the user from writing a particular function multiple times. Once a user-defined file is written, it can be imported anywhere in the program using the #include preprocessor. • In #include directive, comments are not recognized. So in case of #include <a//b>, a//b is treated as filename. • In #include directive, backslash is considered as normal text not escape sequence. So in case of #include <a\nb>, a\nb is treated as filename. • You can use only comment after filename otherwise it will give error.
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/* using #include directive in C language */ #include <stdio.h> int main() { /* * C standard library printf function * defined in the stdio.h header file */ printf("I love you Clementine"); printf("I love you so much"); printf("HappyCodings"); return 0; }
Vector Library end() Function in C++
Return iterator to end. Returns an iterator referring to the past-the-end element in the vector container. The past-the-end element is the theoretical element that would follow the last element in the vector. It does not point to any element, and thus shall not be dereferenced. Because the ranges used by functions of the standard library do not include the element pointed by their closing iterator, this function is often used in combination with vector::begin to specify a range including all the elements in the container. If the container is empty, this function returns the same as vector::begin.
Syntax for Vector end() Function in C++
#include <vector> iterator end() noexcept; const_iterator end() const noexcept;
This function does not accept any parameter. Function returns an iterator to the element past the end of the sequence. If the vector object is const-qualified, the function returns a const_iterator. Otherwise, it returns an iterator. Member types iterator and const_iterator are random access iterator types (pointing to an element and to a const element, respectively). To use vector, include <vector> header. It does not point to the last element, thus to get the last element we can use vector::end()-1.
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed (neither the const nor the non-const versions modify the container). No contained elements are accessed by the call, but the iterator returned can be used to access or modify elements. Concurrently accessing or modifying different elements is safe.
Exception safety
No-throw guarantee: this member function never throws exceptions. The copy construction or assignment of the returned iterator is also guaranteed to never throw.
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/* returns the iterator pointing to the past-the-last element of the vector container by vector::end function code example. */ // CPP program to illustrate implementation of begin() function #include <iostream> #include <string> #include <vector> using namespace std; int main() { // declaration of vector container vector<string> myvector{ "This", "is", "HappyCodings" }; // using begin() to print vector for (auto it = myvector.begin(); it != myvector.end(); ++it) cout << ' ' << *it; return 0; }
main() Function in C++
A program shall contain a global function named main, which is the designated start of the program in hosted environment. main() function is the entry point of any C++ program. It is the point at which execution of program is started. When a C++ program is executed, the execution control goes directly to the main() function. Every C++ program have a main() function.
Syntax for main() Function in C++
void main() { ............ ............ }
void
void is a keyword in C++ language, void means nothing, whenever we use void as a function return type then that function nothing return. here main() function no return any value.
main
main is a name of function which is predefined function in C++ library. In place of void we can also use int return type of main() function, at that time main() return integer type value. 1) It cannot be used anywhere in the program a) in particular, it cannot be called recursively b) its address cannot be taken 2) It cannot be predefined and cannot be overloaded: effectively, the name main in the global namespace is reserved for functions (although it can be used to name classes, namespaces, enumerations, and any entity in a non-global namespace, except that a function called "main" cannot be declared with C language linkage in any namespace). 3) It cannot be defined as deleted or (since C++11) declared with C language linkage, constexpr (since C++11), consteval (since C++20), inline, or static. 4) The body of the main function does not need to contain the return statement: if control reaches the end of main without encountering a return statement, the effect is that of executing return 0;. 5) Execution of the return (or the implicit return upon reaching the end of main) is equivalent to first leaving the function normally (which destroys the objects with automatic storage duration) and then calling std::exit with the same argument as the argument of the return. (std::exit then destroys static objects and terminates the program). 6) (since C++14) The return type of the main function cannot be deduced (auto main() {... is not allowed). 7) (since C++20) The main function cannot be a coroutine.
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/* simple code example by main() function in C++ */ #include <iostream> using namespace std; int main() { int day = 4; switch (day) { case 1: cout << "Monday"; break; case 2: cout << "Tuesday"; break; case 3: cout << "Wednesday"; break; case 4: cout << "Thursday"; break; case 5: cout << "Friday"; break; case 6: cout << "Saturday"; break; case 7: cout << "Sunday"; break; } return 0; }
Vectors in C++ Language
In C++, vectors are used to store elements of similar data types. However, unlike arrays, the size of a vector can grow dynamically. That is, we can change the size of the vector during the execution of a program as per our requirements. Vectors are part of the C++ Standard Template Library. To use vectors, we need to include the vector header file in our program.
Declaration for Vectors in C++
std::vector<T> vector_name;
The type parameter <T> specifies the type of the vector. It can be any primitive data type such as int, char, float, etc.
Initialization for Vectors in C++
// Vector initialization method 1 // Initializer list vector<int> vector1 = {1, 2, 3, 4, 5};
We are initializing the vector by providing values directly to the vector. vector1 is initialized with values 1, 2, 3, 4, 5.
// Vector initialization method 2 vector<int> vector3(5, 12);
Here, 5 is the size of the vector and 8 is the value. This code creates an int vector with size 5 and initializes the vector with the value of 8. So, the vector is equivalent to
vector<int> vector2 = {8, 8, 8, 8, 8};
The vector class provides various methods to perform different operations on vectors. Add Elements to a Vector: To add a single element into a vector, we use the push_back() function. It inserts an element into the end of the vector. Access Elements of a Vector: In C++, we use the index number to access the vector elements. Here, we use the at() function to access the element from the specified index. Change Vector Element: We can change an element of the vector using the same at() function. Delete Elements from C++ Vectors: To delete a single element from a vector, we use the pop_back() function. In C++, the vector header file provides various functions that can be used to perform different operations on a vector. • size(): returns the number of elements present in the vector. • clear(): removes all the elements of the vector. • front(): returns the first element of the vector. • back(): returns the last element of the vector. • empty(): returns 1 (true) if the vector is empty. • capacity(): check the overall size of a vector. Vector iterators are used to point to the memory address of a vector element. In some ways, they act like pointers.
Syntax for Vector Iterators in C++
vector<T>::iterator iteratorName;
We can initialize vector iterators using the begin() and end() functions. The begin() function returns an iterator that points to the first element of the vector. The end() function points to the theoretical element that comes after the final element of the vector.
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/* Vectors in C++ language */ // C++ program to illustrate the capacity function in vector #include <iostream> #include <vector> using namespace std; int main() { vector<int> myvector; for (int i = 1; i <= 5; i++) myvector.push_back(i); cout << "Size : " << myvector.size(); cout << "\nCapacity : " << myvector.capacity(); cout << "\nMax_Size : " << myvector.max_size(); // resizes the vector size to 4 myvector.resize(4); // prints the vector size after resize() cout << "\nSize : " << myvector.size(); // checks if the vector is empty or not if (myvector.empty() == false) cout << "\nVector is not empty"; else cout << "\nVector is empty"; // Shrinks the vector myvector.shrink_to_fit(); cout << "\nVector elements are: "; for (auto it = myvector.begin(); it != myvector.end(); it++) cout << *it << " "; return 0; }
sizeof() Operator in C++
The sizeof() is an operator that evaluates the size of data type, constants, variable. It is a compile-time operator as it returns the size of any variable or a constant at the compilation time. The size, which is calculated by the sizeof() operator, is the amount of RAM occupied in the computer. The sizeof is a keyword, but it is a compile-time operator that determines the size, in bytes, of a variable or data type. The sizeof operator can be used to get the size of classes, structures, unions and any other user defined data type.
Syntax for sizeof() Operator in C++
sizeof(data_type);
data_type
data type whose size is to be calculated The data_type can be the data type of the data, variables, constants, unions, structures, or any other user-defined data type. If the parameter of a sizeof() operator contains the data type of a variable, then the sizeof() operator will return the size of the data type. sizeof() may give different output according to machine, we have run our program on 32 bit gcc compiler.
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/* The sizeof() is an operator in C and C++. It is an unary operator which assists a programmer in finding the size of the operand which is being used. */ #include <iostream> using namespace std; int main() { int arr[]={10,20,30,40,50}; std::cout << "Size of the array 'arr' is : "<<sizeof(arr) << std::endl; cout << "Size of char : " << sizeof(char) << endl; cout << "Size of int : " << sizeof(int) << endl; cout << "Size of short int : " << sizeof(short int) << endl; cout << "Size of long int : " << sizeof(long int) << endl; cout << "Size of float : " << sizeof(float) << endl; cout << "Size of double : " << sizeof(double) << endl; cout << "Size of wchar_t : " << sizeof(wchar_t) << endl; return 0; }
IOS Library eof() Function in C++
Check whether eofbit is set. Returns true if the eofbit error state flag is set for the stream. This flag is set by all standard input operations when the End-of-File is reached in the sequence associated with the stream. Note that the value returned by this function depends on the last operation performed on the stream (and not on the next). Operations that attempt to read at the End-of-File fail, and thus both the eofbit and the failbit end up set. This function can be used to check whether the failure is due to reaching the End-of-File or to some other reason.
Syntax for IOS eof() Function in C++
bool eof() const;
This function does not accept any parameter. Function returns true if the stream's eofbit error state flag is set (which signals that the End-of-File has been reached by the last input operation). false otherwise.
Data races
Accesses the stream object. Concurrent access to the same stream object may cause data races.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the stream.
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/* The eof() method of ios class in C++ is used to check if the stream is has raised any EOF (End Of File) error. It means that this function will check if this stream has its eofbit set. */ // C++ code example to demonstrate the working of eof() function #include <iostream> #include <fstream> int main () { std::ifstream is("example.txt"); char c; while (is.get(c)) std::cout << c; if (is.eof()) std::cout << "[EoF reached]\n"; else std::cout << "[error reading]\n"; is.close(); return 0; }
Vector Library begin() Function in C++
Return iterator to beginning. Returns an iterator pointing to the first element in the vector. Notice that, unlike member vector::front, which returns a reference to the first element, this function returns a random access iterator pointing to it. If the container is empty, the returned iterator value shall not be dereferenced. The C++ function std::vector::begin() returns a random access iterator pointing to the first element of the vector.
Syntax for Vector begin() Function in C++
#include <vector> iterator begin() noexcept; const_iterator begin() const noexcept;
This function does not accept any parameter. Function returns an iterator to the beginning of the sequence container. If the vector object is const-qualified, the function returns a const_iterator. Otherwise, it returns an iterator. Member types iterator and const_iterator are random access iterator types (pointing to an element and to a const element, respectively).
Complexity
Constant
Iterator validity
No changes
Data races
The container is accessed (neither the const nor the non-const versions modify the container). No contained elements are accessed by the call, but the iterator returned can be used to access or modify elements. Concurrently accessing or modifying different elements is safe.
Exception safety
No-throw guarantee: this member function never throws exceptions. The copy construction or assignment of the returned iterator is also guaranteed to never throw.
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/* returns a random access iterator pointing to the first element of the vector by std::vector::begin() function code example. */ // CPP program to illustrate implementation of begin() function #include <iostream> #include <string> #include <vector> using namespace std; int main() { // declaration of vector container vector<string> myvector{ "This", "is", "HappyCodings" }; // using begin() to print vector for (auto it = myvector.begin(); it != myvector.end(); ++it) cout << ' ' << *it; return 0; }
Iterators in C++ Language
Iterators are just like pointers used to access the container elements. Iterators are one of the four pillars of the Standard Template Library or STL in C++. An iterator is used to point to the memory address of the STL container classes. For better understanding, you can relate them with a pointer, to some extent. Iterators act as a bridge that connects algorithms to STL containers and allows the modifications of the data present inside the container. They allow you to iterate over the container, access and assign the values, and run different operators over them, to get the desired result.
Syntax for Iterators in C++
<ContainerType> :: iterator; <ContainerType> :: const_iterator;
• Iterators are used to traverse from one element to another element, a process is known as iterating through the container. • The main advantage of an iterator is to provide a common interface for all the containers type. • Iterators make the algorithm independent of the type of the container used. • Iterators provide a generic approach to navigate through the elements of a container. Operator (*) : The '*' operator returns the element of the current position pointed by the iterator. Operator (++) : The '++' operator increments the iterator by one. Therefore, an iterator points to the next element of the container. Operator (==) and Operator (!=) : Both these operators determine whether the two iterators point to the same position or not. Operator (=) : The '=' operator assigns the iterator. Iterators can be smart pointers which allow to iterate over the complex data structures. A Container provides its iterator type. Therefore, we can say that the iterators have the common interface with different container type. The container classes provide two basic member functions that allow to iterate or move through the elements of a container: begin(): The begin() function returns an iterator pointing to the first element of the container. end(): The end() function returns an iterator pointing to the past-the-last element of the container. Input Iterator: An input iterator is an iterator used to access the elements from the container, but it does not modify the value of a container. Operators used for an input iterator are: Increment operator(++), Equal operator(==), Not equal operator(!=), Dereference operator(*). Output Iterator: An output iterator is an iterator used to modify the value of a container, but it does not read the value from a container. Therefore, we can say that an output iterator is a write-only iterator. Operators used for an output iterator are: Increment operator(++), Assignment operator(=). Forward Iterator: A forward iterator is an iterator used to read and write to a container. It is a multi-pass iterator. Operators used for a Forward iterator are: Increment operator(++), Assignment operator(=), Equal operator(=), Not equal operator(!=). Bidirectional iterator: A bidirectional iterator is an iterator supports all the features of a forward iterator plus it adds one more feature, i.e., decrement operator(--). We can move backward by decrementing an iterator. Operators used for a Bidirectional iterator are: Increment operator(++), Assignment operator(=), Equal operator(=), Not equal operator(!=), Decrement operator(--). Random Access Iterator: A Random Access iterator is an iterator provides random access of an element at an arbitrary location. It has all the features of a bidirectional iterator plus it adds one more feature, i.e., pointer addition and pointer subtraction to provide random access to an element. Following are the disadvantages of an iterator: • If we want to move from one data structure to another at the same time, iterators won't work. • If we want to update the structure which is being iterated, an iterator won?t allow us to do because of the way it stores the position. • If we want to backtrack while processing through a list, the iterator will not work in this case. Following are the advantages of an iterator: • Ease in programming: It is convenient to use iterators rather than using a subscript operator[] to access the elements of a container. If we use subscript operator[] to access the elements, then we need to keep the track of the number of elements added at the runtime, but this would not happen in the case of an iterator. • Code Reusability: A code can be reused if we use iterators. In the above example, if we replace vector with the list, and then the subscript operator[] would not work to access the elements as the list does not support the random access. However, we use iterators to access the elements, then we can also access the list elements. • Dynamic Processing: C++ iterators provide the facility to add or delete the data dynamically.
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/* Iterators in C++ language */ // C++ code to demonstrate the working of next() and prev() #include<iostream> #include<iterator> // for iterators #include<vector> // for vectors using namespace std; int main() { vector<int> ar = { 1, 2, 3, 4, 5 }; // Declaring iterators to a vector vector<int>::iterator ptr = ar.begin(); vector<int>::iterator ftr = ar.end(); // Using next() to return new iterator // points to 4 auto it = next(ptr, 3); // Using prev() to return new iterator // points to 3 auto it1 = prev(ftr, 3); // Displaying iterator position cout << "The position of new iterator using next() is : "; cout << *it << " "; cout << endl; // Displaying iterator position cout << "The position of new iterator using prev() is : "; cout << *it1 << " "; cout << endl; return 0; }
Algorithm Library copy() Function in C++
copy() function is used to copy items from one iterator to another iterator with a specific range. We can define the start and end position of the source and it will copy all items in this rage to a different destination. To use copy() function, we need to include <bits/stdc+.h> or header file. It copies all the elements pointed by first and last. first element is included in the output but last is not. output is the start position of the final result iterator. It returns one iterator to the end of the destination range where elements have been copied.
Syntax for copy() Function in C++
template <class InputIterator, class OutputIterator> OutputIterator copy (InputIterator first, InputIterator last, OutputIterator result);
first
It is an input iterator to the first element of the range, where the element itself is included in the range.
last
It is an input iterator to the last element of the range, where the element itself is not included in the range. Input iterators to the initial and final positions in a sequence to be copied. The range used is [first,last), which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.
result
It is an output iterator to the first element of the new container in which the elements are copied. Output iterator to the initial position in the destination sequence. This shall not point to any element in the range [first,last). Function returns an iterator to the end of the destination range where elements have been copied.
Complexity
Linear in the distance between first and last: Performs an assignment operation for each element in the range.
Data races
The objects in the range [first,last) are accessed (each object is accessed exactly once). The objects in the range between result and the returned value are modified (each object is modified exactly once).
Exceptions
Throws if either an element assignment or an operation on iterators throws. Note that invalid arguments cause undefined behavior.
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/* copying the array elements to the vector by copy() function code example */ // C++ STL program to demonstrate use of std::copy() function #include <iostream> #include <algorithm> #include <vector> using namespace std; int main() { //declaring & initializing an int array int arr[] = { 10, 20, 30, 40, 50 }; //vector declaration vector<int> v1(5); //copying array elements to the vector copy(arr, arr + 5, v1.begin()); //printing array cout << "arr: "; for (int x : arr) cout << x << " "; cout << endl; //printing vector cout << "v1: "; for (int x : v1) cout << x << " "; cout << endl; return 0; }


This C++ Program implements The "B-Tree" data structure. B-tree is a tree data structure that keeps "data sorted" and allows searches, sequential access & insertions in logarithmic
To sort an array in ascending order by bubble sort in C++ language, you have to ask to user to enter the array size then ask to enter array elements, start sorting the array elements by