C++ Programming Code Examples
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Use map to store the value of the month name and its day number
/* Use map to store the value of the month name and its day number */
#include <map>
#include <iostream>
#include <string>
using namespace std;
class ltstr{
public:
bool operator()(const char* s1, const char* s2) const
{ return (strcmp(s1, s2) < 0);}
};
int main(void)
{
map<const char*, int, ltstr> months;
months["January"] = 31;
months["February"] = 28;
months["March"] = 31;
months["April"] = 30;
months["May"] = 31;
months["June"] = 30;
months["July"] = 31;
months["August"] = 31;
months["September"] = 30;
months["October"] = 31;
months["November"] = 30;
months["December"] = 31;
cout << "june -> " << months["June"] << endl;
map<const char*, int, ltstr>::iterator cur = months.find("June");
map<const char*, int, ltstr>::iterator prev = cur;
map<const char*, int, ltstr>::iterator next = cur;
++next;
--prev;
cout << "Previous (in alphabetical order) is " << (*prev).first << endl;
cout << "Next (in alphabetical order) is " << (*next).first << endl;
}
#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.
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.
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.
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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.
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