C++ STL algorithm, merge() program example

Compiler: Visual C++ Express Edition 2005

Compiled on Platform: Windows XP Pro SP2

Additional project setting: Set project to be compiled as C++

Project -> your_project_name Properties -> Configuration Properties -> C/C++ -> Advanced -> Compiled As: Compiled as C++ Code (/TP)

Other info: none

To do: Using the C++ merge() to combine all the elements from two sorted source ranges into a single, sorted destination range, where the ordering criterion may be specified by a binary predicate in C++ programming

To show: How to use the algorithm, merge() to combine all the elements from two sorted source ranges into a single, sorted destination range, where the ordering criterion may be specified by a binary predicate in C++ programming

// C++ STL algorithm, merge()

#include <vector>

#include <algorithm>

// for greater<int>()

#include <functional>

#include <iostream>

using namespace std;

// return whether modulus of elem1 is less than modulus of elem2

bool mod_lesser(int elem1, int elem2)

{

if(elem1 < 0)

elem1 = - elem1;

if(elem2 < 0)

elem2 = - elem2;

return (elem1 < elem2);

}

int main(void)

{

// containers

vector <int> vec1a, vec1b, vec1(12);

// iterators

vector <int>::iterator Iter1a, Iter1b, Iter1;

int i, j;

// constructing vector vec1a and vec1b with default less than ordering

// pushing data

for(i = 0; i <= 5; i++)

vec1a.push_back(i);

for(j =-5; j <= 0; j++)

vec1b.push_back(j);

// printing data

cout<<"vec1a vector data with range sorted by the binary predicate less than is: ";

for(Iter1a = vec1a.begin(); Iter1a != vec1a.end(); Iter1a++)

cout<<*Iter1a<<" ";

cout<<endl;

cout<<"vec1b vector data with range sorted by the binary predicate less than is: ";

for(Iter1b = vec1b.begin(); Iter1b != vec1b.end(); Iter1b++)

cout<<*Iter1b<<" ";

cout<<endl;

// constructing vector vec2 with ranges sorted by greater

vector <int> vec2a(vec1a), vec2b(vec1b), vec2(vec1);

vector <int>::iterator Iter2a, Iter2b, Iter2;

sort(vec2a.begin(), vec2a.end(), greater<int>());

sort(vec2b.begin(), vec2b.end(), greater<int>());

cout<<"vec2a vector data with range sorted by the binary predicate greater is: ";

for(Iter2a = vec2a.begin(); Iter2a != vec2a.end(); Iter2a++)

cout<<*Iter2a<<" ";

cout<<endl;

cout<<"vec2b vector data with range sorted by the binary predicate greater is: ";

for(Iter2b = vec2b.begin(); Iter2b != vec2b.end(); Iter2b++)

cout<<*Iter2b<<" ";

cout<<endl;

// constructing vector vec3 with ranges sorted by mod_lesser

vector <int> vec3a(vec1a), vec3b(vec1b), vec3(vec1);

vector <int>::iterator Iter3a, Iter3b, Iter3;

sort(vec3a.begin(), vec3a.end(), mod_lesser);

sort(vec3b.begin(), vec3b.end(), mod_lesser);

cout<<"vec3a vector data with range sorted by the binary predicate mod_lesser is: ";

for(Iter3a = vec3a.begin(); Iter3a != vec3a.end(); Iter3a++)

cout<<*Iter3a<<" ";

cout<<endl;

cout<<"vec3b vector data with range sorted by the binary predicate mod_lesser is: ";

for(Iter3b = vec3b.begin(); Iter3b != vec3b.end(); Iter3b++)

cout<<*Iter3b<<" ";

cout<<endl;

// to merge in ascending order with default binary predicate less <int>()

cout<<"\nOperation: merge(vec1a.begin(),vec1a.end(),vec1b.begin(),vec1b.end(),vec1.begin())"<<endl;

merge(vec1a.begin(), vec1a.end(), vec1b.begin(), vec1b.end(), vec1.begin());

cout<<"vec1merg vector data, merged with default order: ";

for(Iter1 = vec1.begin(); Iter1 != vec1.end(); Iter1++)

cout<<*Iter1<<" ";

cout<<endl;

// to merge in descending order, specify binary predicate greater<int>()

cout<<"\nOperation: merge(vec2a.begin(),vec2a.end(),vec2b.begin(),vec2b.end(),vec2.begin(),greater<int>())"<<endl;

merge(vec2a.begin(), vec2a.end(), vec2b.begin(), vec2b.end(), vec2.begin(), greater<int>());

cout<<"vec2merg vector data, merged with binary predicate greater() is: ";

for(Iter2 = vec2.begin(); Iter2 != vec2.end(); Iter2++)

cout<<*Iter2<<" ";

cout<<endl;

// applying a user-defined binary predicate mod_lesser

cout<<"\nOperation: merge(vec3a.begin(),vec3a.end(), vec3b.begin(),vec3b.end(),vec3.begin(),mod_lesser)"<<endl;

merge(vec3a.begin(), vec3a.end(), vec3b.begin(), vec3b.end(), vec3.begin(), mod_lesser);

cout<<"vec3merg vector data, merged with binary predicate mod_lesser() is: ";

for(Iter3 = vec3.begin(); Iter3 != vec3.end(); Iter3++)

cout<<*Iter3<<" ";

cout<<endl;

return 0;

}

Output examples:

vec1a vector data with range sorted by the binary predicate less than is: 0 1 2 3 4 5

vec1b vector data with range sorted by the binary predicate less than is: -5 -4 -3 -2 -1 0

vec2a vector data with range sorted by the binary predicate greater is: 5 4 3 2 1 0

vec2b vector data with range sorted by the binary predicate greater is: 0 -1 -2 -3 -4 -5

vec3a vector data with range sorted by the binary predicate mod_lesser is: 0 1 2 3 4 5

vec3b vector data with range sorted by the binary predicate mod_lesser is: 0 -1 -2 -3 -4 -5

Operation: merge(vec1a.begin(),vec1a.end(),vec1b.begin(),vec1b.end(),vec1.begin())

vec1merg vector data, merged with default order: -5 -4 -3 -2 -1 0 0 1 2 3 4 5

Operation: merge(vec2a.begin(),vec2a.end(),vec2b.begin(),vec2b.end(),vec2.begin(),greater<int>())

vec2merg vector data, merged with binary predicate greater() is: 5 4 3 2 1 0 0 -1 -2 -3 -4 -5

Operation: merge(vec3a.begin(),vec3a.end(), vec3b.begin(),vec3b.end(),vec3.begin(),mod_lesser)

vec3merg vector data, merged with binary predicate mod_lesser() is: 0 0 1 -1 2 -2 3 -3 4 -4 5 -5

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