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Demonstrating an STL map
/* Demonstrating an STL map */
#include <iostream>
#include <map>
#include <string>
using namespace std;
int main()
{
map<string, long> directory;
directory["A"] = 1234567;
directory["B"] = 9876543;
directory["C"] = 3459876;
string name = "A";
if (directory.find(name) != directory.end())
cout << "The phone number for " << name
<< " is " << directory[name] << "\n";
else
cout << "Sorry, no listing for " << name << "\n";
return 0;
}
/*
The phone number for A is 1234567
*/
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.
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.
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.
Get iterator to element. Searches the container for an element with a key equivalent to k and returns an iterator to it if found, otherwise it returns an iterator to map::end. Two keys are considered equivalent if the container's comparison object returns false reflexively (i.e., no matter the order in which the elements are passed as arguments). Another member function, map::count, can be used to just check whether a particular key exists. The function accepts one mandatory parameter key which specifies the key to be searched in the map container.
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.
Return iterator to end. Returns an iterator referring to the past-the-end element in the map container. The past-the-end element is the theoretical element that would follow the last element in the map container. 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 map::begin to specify a range including all the elements in the container. If the container is empty, this function returns the same as map::begin.
Relational operators for map. Performs the appropriate comparison operation between the map containers lhs and rhs. The equality comparison (operator==) is performed by first comparing sizes, and if they match, the elements are compared sequentially using operator==, stopping at the first mismatch (as if using algorithm equal). The less-than comparison (operator<) behaves as if using algorithm lexicographical_compare, which compares the elements sequentially using operator< in a reciprocal manner (i.e., checking both a<b and b<a) and stopping at the first occurrence.
In computer programming, we use the if statement to run a block code only when a certain condition is met. An if statement can be followed by an optional else statement, which executes when the boolean expression is false. There are three forms of if...else statements in C++: • if statement, • if...else statement, • if...else if...else statement, The if statement evaluates the condition inside the parentheses ( ). If the condition evaluates to true, the code inside the body of if is executed. If the condition evaluates to false, the code inside the body of if is skipped.
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