C++ Programming Code Examples
C++ > Code Snippets Code Examples
Map erase
/* Map erase */
#include <map>
#include <iostream>
using namespace std;
class Data
{
public:
Data(int val = 0) { mVal = val; }
int getVal() const { return mVal; }
void setVal(int val) {mVal = val; }
protected:
int mVal;
};
int main(int argc, char** argv)
{
map<int, Data> dataMap;
dataMap[1] = Data(4);
cout << "There are " << dataMap.count(1) << " elements with key 1\n";
dataMap.erase(1);
cout << "There are " << dataMap.count(1) << " elements with key 1\n";
return (0);
}
The main purpose of C++ programming is to add object orientation to the C programming language and classes are the central feature of C++ that supports object-oriented programming and are often called user-defined types. A class is used to specify the form of an object and it combines data representation and methods for manipulating that data into one neat package. The data and functions within a class are called members of the class.
Erase elements. Removes from the map container either a single element or a range of elements ([first,last)). The C++ map::erase function is used to delete either a single element or a range of elements from the map. It reduces the size of the map by number of elements deleted from the container. This effectively reduces the container size by the number of elements removed, which are destroyed.
Count elements with a specific key. Searches the container for elements with a key equivalent to k and returns the number of matches. The map::count() is a built-in function in C++ STL which returns 1 if the element with key K is present in the map container. It returns 0 if the element with key K is not present in the container. Because all elements in a map container are unique, the function can only return 1 (if the element is found) or zero (otherwise). Two keys are considered equivalent if the container's comparison object returns false reflexively (i.e., no matter the order in which the keys are passed as arguments). Function returns 1 if the container contains an element whose key is equivalent to k, or zero otherwise.
In C++, constructor is a special method which is invoked automatically at the time of object creation. It is used to initialize the data members of new object generally. The constructor in C++ has the same name as class or structure. Constructors are special class functions which performs initialization of every object. The Compiler calls the Constructor whenever an object is created. Constructors initialize values to object members after storage is allocated to the object. Whereas, Destructor on the other hand is used to destroy the class object. • Default Constructor: A constructor which has no argument is known as default constructor. It is invoked at the time of creating object.
Maps are associative containers that store elements in a mapped fashion. Each element has a key value and a mapped value. No two mapped values can have the same key values. Maps are part of the C++ STL (Standard Template Library). Maps are the associative containers that store sorted key-value pair, in which each key is unique and it can be inserted or deleted but cannot be altered. Values associated with keys can be changed. The key values are good for sorting and identifying elements uniquely. The mapped values are for storing content associated with the key. The two may differ in types, but the member type combines them via a pair type that combines both.
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.
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.
Access element. If k matches the key of an element in the container, the function returns a reference to its mapped value. This operator is used to reference the element present at position given inside the operator. It is similar to the at() function, the only difference is that the at() function throws an out-of-range exception when the position is not in the bounds of the size of map, while this operator causes undefined behavior. If k does not match the key of any element in the container, the function inserts a new element with that key and returns a reference to its mapped value. Notice that this always increases the container size by one, even if no mapped value is assigned to the element (the element is constructed using its default constructor). A similar member function, map::at, has the same behavior when an element with the key exists, but throws an exception when it does not.
#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.
To check whether the input alphabet is vowel or not a vowel in C++, Enter a Character, then check the character for Vowel. The character is vowel, only if it's equal to a, A, e, E, i, I, o, O
