The sample code below illustrates how to use the map::max_size, clear, erase,
and size
STL functions in Visual C++.
Required Header:
<map>
size_type max_size() const;
void clear() const;
bool empty() const;
iterator erase(iterator first, iterator last);
size_type size() const;
A::reference operator[](const Key& key); // A is the allocator
iterator map::begin();
iterator map::end();
iterator map::find(const Key& key);
Note: The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.
Description:
The following sample creates a map of strings to ints and fills it first with a map of month names to month numbers, then empties and refills it with a map of weekday names to corresponding ints.
Sample Code:
//////////////////////////////////////////////////////////////////////
//
// Compile options needed: None
//
// <filename> : main.cpp
//
// Functions: iterator map::max_size();
// void clear() const;
// bool empty() const;
// iterator erase(iterator first, iterator last);
// size_type size() const;
// A::reference operator[](const Key& key);
// iterator map::begin();
// iterator map::end();
// iterator map::find(const Key& key);
//////////////////////////////////////////////////////////////////////
#pragma warning(disable:4786)
#include <iostream>
#include <string>
#include <map>
using namespace std ;
typedef map<string, int> STRING2INT;
void main()
{
STRING2INT MyMap;
STRING2INT::iterator MyIterator;
string MyBuffer;
// print the maximum number of <key,data> pairs that MyMap can hold
cout << "MyMap is capable of holding " << MyMap.max_size()
<< " <string,int> pairs" << endl;
if(!MyMap.empty())
cout << "MyMap has " << MyMap.size() << " entries" << endl;
else
cout << "MyMap is empty" << endl;
cout << "Entering new entries in MyMap" << endl;
// Fill in MyMap with the months of the year, mapped to their number
// January - 1, February - 2, etc. using operator[].
MyMap["January"] = 1;
MyMap["February"] = 2;
MyMap["March"] = 3;
MyMap["April"] = 4;
MyMap["May"] = 5;
MyMap["June"] = 6;
MyMap["July"] = 7;
MyMap["August"] = 8;
MyMap["September"] = 9;
MyMap["October"] = 10;
MyMap["November"] = 11;
MyMap["December"] = 12;
if(!MyMap.empty())
cout << "MyMap has " << MyMap.size() << " entries" << endl;
else
cout << "MyMap is empty" << endl;
// Ask the user for a month of the year and print the number
// that corresponds to the month entered
//MyIterator = MyMap.end();
while(MyIterator == MyMap.end()){
cout << "Enter a Month :";
cin >> MyBuffer;
if((MyIterator = MyMap.find(MyBuffer)) != MyMap.end())
cout << (*MyIterator).first << " is Month Number "
<< (*MyIterator).second << endl;
else
cout << "Enter a Valid Month (example: March)" << endl;
}
// empty MyMap - note that clear simply calls erase(begin(),end());
MyMap.clear();
if(!MyMap.empty())
cout << "MyMap has " << MyMap.size() << " entries" << endl;
else
cout << "MyMap is empty" << endl;
cout << "Entering new entries in MyMap" << endl;
// Fill MyMap with the days of the week, each mapped to an int
MyMap["Monday"] = 1;
MyMap["Tuesday"] = 2;
MyMap["Wednesday"] = 3;
MyMap["Thursday"] = 4;
MyMap["Friday"] = 5;
MyMap["Saturday"] = 6;
MyMap["Sunday"] = 7;
if(!MyMap.empty())
cout << "MyMap has " << MyMap.size() << " entries" << endl;
else
cout << "MyMap is empty" << endl;
// Ask the user for a day of the week and print the number
// that corresponds to the day entered
MyIterator = MyMap.end();
while(MyIterator == MyMap.end()){
cout << "Enter a Day of the Week:";
cin >> MyBuffer;
if((MyIterator = MyMap.find(MyBuffer)) != MyMap.end())
cout << (*MyIterator).first << " is Day Number "
<< (*MyIterator).second << endl;
else
cout <<"Enter a Valid Day of the Week(example: Monday)"<< endl;
}
// Now clear MyMap again - this time using erase instead of clear
MyMap.erase(MyMap.begin(), MyMap.end());
if(!MyMap.empty())
cout << "MyMap has " << MyMap.size() << " entries" << endl;
else
cout << "MyMap is empty" << endl;
}
Program Output is:
MyMap is capable of holding 1073741823 <string,int> pairs
MyMap is empty
Entering new entries in MyMap
MyMap has 12 entries
Enter a Month :[April]
April is Month Number 4
MyMap is empty
Entering new entries in MyMap
MyMap has 7 entries
Enter a Day of the Week:[Friday]
Enter a Valid Day of the Week(example: Monday)
Enter a Day of the Week:[Friday]
Friday is Day Number 5
MyMap is empty