[note 1]
Function templates
template <class T>
return-type function-name (arguments of type T)
{
function body
}
在这里插入代码片
[example 1]
#include <iostream>
using namespace std;
template<class T>
void Swap(T &x, T &y)
{
T temp=x;
x=y;
y=temp;
}
void fun(int m, int n,float a,float b)
{
cout << "m and n before swap: " << m << " " << n << "\n";
Swap(m,n);
cout << "m and n after swap: " << m << " " << n << "\n";
cout << "a and b before swap: " << a << " " << b << "\n";
Swap(a,b);
cout << "a and b after swap: " << a << " " << b << "\n";
}
int main()
{
fun(100,200,11.22,33.44);
return 0;
}
[note 2]
- C++ will not perform any implicit conversion for the template arguments.
[solution 1]
explicit type conversion
cout<<"the min of 2 and 3.2 is:"<<min(double(2),3.2)<<endl;
[solution 2]
specify the argument’s data type explicitly
cout<<"the min of 2 and 3.2 is:"<<min<double>(2,3.2)<<endl;
[solution 3]
specify multiple parameters for function template.
#include<iostream>
#include<cstring>
using namespace std;
template<class T1, class T2>
void display(T1 x, T2 y){cout << x << " " << y << "\n";}
int main()
{
display(1999,"EBG");
display(12.34,1234);
return 0;
}
[note 3]
The return type depend on the template parameter T1 (the first parameter).
[note 4]
class template
template<class T, int size>
class array
{
T a[size];
}
to create a object:
array<int, 10> a1;
[note 5]
shows how a template function is overloaded with an explicit function.
#include<iostream>
#include<string>
using namespace std;
template<class T>
void display(T x){cout<<"Template display: "<<x<<"\n";}
void display(int x){cout<<"Explicit display: "<<x<<"\n";} //Overloads the generic display()
int main()
{
display(100); //Invokes the ordinary version of display() and not the template version.
display(12.34);
display('C');
return 0;
}
[note 6]
Member function templates
template<class T>
return-type classname<T>::functionname(arglist)
{
//
}
[note 7]
Three key components of STL:
- containers
- algorithms
- iterators
[note 8]
STL-vector
#include<iostream>
#include<vector> //Vector header file
using namespace std;
void display(vector<int> &v)
{
//Size(): The member function gives the current size of the vector.
for(int i=0;i<v.size();i++){cout << v[i] << " ";}
cout << "\n";
}
int main()
{
vector<int> v; //Create a vector of type int
cout << "Initial size = " << v.size() << "\n"; //Gives the current size of the vector
//Putting values into the vector
int x;
cout << "Enter five integer values: ";
for(int i=0;i<5;i++)
{
cin >> x;
//member function used to put five values into the vector
v.push_back(x); //Takes a value as its argument and adds it to the back end of the vector.
}
cout << "Size after adding 5 values: ";
cout << v.size() << "\n";
//Display the contents
cout << "Current contents: \n";
display(v);
//Add one more value
v.push_back(6.6); //float value truncated to int and then puts it into the vector at its back end(Since the vector v is of type int, it can accept only integer values )
//Display size and contents
cout << "\nSize = " << v.size() << "\n";
cout << "Contents now: \n";
display(v);
//Inserting elements
vector<int>::iterator itr = v.begin(); //iterator(point to the first position of the vector)
itr = itr + 3; //itr points to 4th element
v.insert(itr,1,9);
//Display the contents
cout << "\nContents after inserting: \n";
display(v);
//Removing 4th and 5th elements
v.erase(v.begin()+3,v.begin()+5); //Removes 4th and 5th element from the vector
//Display the contents
cout << "\nContents after deletion: \n";
display(v);
cout << "END\n";
return(0);
}
output:
Initial size = 0
Enter five integer values:
1
2
3
4
5
Size after adding 5 values: 5
Current contents:
1 2 3 4 5
Size = 6
Contents now:
1 2 3 4 5 6
Contents after inserting:
1 2 3 9 4 5 6
Contents after deletion:
1 2 3 5 6
END
[note 9]
STL-list
#include<iostream>
#include<list>
#include<cstdlib> //For using rand() function
using namespace std;
void display(list<int> &lst)
{
list<int>::iterator p;
for(p=lst.begin(); p!=lst.end(); ++p)
cout << *p << ", ";
cout << "\n\n";
}
int main()
{
list<int> list1; //Empty list1 of zero length
list<int> list2(5); //Empty list2 of size 5
for(int i=0; i<3; i++) //List1 filled with three values using the member function push_back() and math function rand()
list1.push_back(rand()/100);
list<int>::iterator p;
//List2 filled using a list type iterator p and a for loop
for(p=list2.begin(); p!=list2.end(); ++p) //list2.begin() gives the position of the first element and list2.end() gives the position immediately after the last element.
*p=rand()/100;
cout << "List1 \n";
display(list1);
cout << "List2 \n";
display(list2);
//Add two elements at both the ends of list1
list1.push_front(100);
list1.push_back(200);
//Remove an element at the front of list2(Similarly, we may use pop_back() to remove the last element.)
list2.pop_front();
cout << "Now list1 \n";
display(list1);
cout << "Now list2 \n";
display(list2);
list<int> listA, listB;
//The objects of list can be initialized with other list objects illustrated as follows
listA=list1;
listB=list2;
//Merging two lists(unsorted)
list1.merge(list2); //Adds the list2 elements to the end of list1.
cout << "Merged unsorted list2 \n";
display(list1);
//Sorting and merging
listA.sort(); //The element in a list may be sorted in increasing order using sort() member function.
listB.sort(); //Note that when two sorted lists are merged, the elements are inserted in appropriate locations and therefore the merged list is also a sorted one.
listA.merge(listB);
cout << "Merged sorted lists \n";
display(listA); //Display the contents of various lists.(Note the difference between the implementation of display() in Program 14.1 and Program 14.2.)
//Reversing a list
listA.reverse();
cout << "Reversed merged list \n";
display(listA);
return(0);
}
[note 10]
STL-maps
#include<iostream>
#include<string>
#include<map>
using namespace std;
int main()
{
string name[]={"aa","bb","cc"};
double salary[]={1200,2000,1450};
map<string,double>sal;
map<string,double>::iterator p;
for(int i=0;i<3;i++)
sal.insert(make_pair(name[i],salary[i]));
sal["tom"]=3400;
sal["bob"]=2000;
for(p=sal.begin();p!=sal.end();p++)
cout<<p->first<<"\t"<<p->second<<endl;
string person;
cout<<"Name of the person to be searched: ";
cin>>person;
for(p=sal.begin();p!=sal.end();p++)
if(p->first==person)
cout<<p->second<<endl;
return 0;
}
