sort a 'std::vector' containing classes/structures?

Hi,

I want to sort a vector contain some data using std::sort. Here are the sample codes.

#include <vector>
#include <string>
#include <iostream>
#include <algorithm>

using namespace std;

class MyData
{
public:
 int m_iData;
 string m_strSomeOtherData;
};

bool MyDataSortPredicate(const MyData& lhs, const MyData& rhs)
{
 return lhs.m_iData < rhs.m_iData;
}

int main()
{
 // Create list
 vector myvector;

 // Add data to the vector
 MyData data;
 data.m_iData = 3;
 myvector.push_back(data);
 data.m_iData = 1;
 myvector.push_back(data);

 // Sort the vector using predicate and std::sort
 std::sort(myvector.begin(), myvector.end(), MyDataSortPredicate);

 // Dump the vector to check the result
 for (vector::const_iterator citer = myvector.begin();
   citer != myvector.end(); ++citer)
 {
  cout << (*citer).m_iData << endl;
 }

 return 0;
}

This program works well. However, the function "MyDataSortPredicate" is a global function. How could I make it a member function of the "MyData" class Thanks.

-Jim

Visual C++11

You can move that function into the class and declare it as static. (static bool MyDataSortPredicate() {...}). Nothing else changes (i.e. it does not have a this pointer), except you now pass &MyData::MyDataSortPredicate into std::sort. Note that VS2005 now requires & to get addresses of functions, whereas VS2003 just made it optional.

Brian Kramer wrote:
You can move that function into the class and declare it as static. (static bool MyDataSortPredicate() {...}). Nothing else changes (i.e. it does not have a this pointer), except you now pass &MyData::MyDataSortPredicate into std::sort. Note that VS2005 now requires & to get addresses of functions, whereas VS2003 just made it optional.

Thank you very much.

You can also write a function object:

class MyDataSorter

{

public:

bool operator()(const MyData& lhs, const MyData& rhs)

{

return lhs.m_iData < rhs.m_iData;

}
};

std::sort(myvector.begin(), myvector.end(), MyDataSorter());

PS: did not test the code

Be careful when storing objects in STL containers by value without any custom copy constructors. You need one for deep copy.

valikac

Marius, functors are cool! I use them in my bit vector implementation (i.e. enumerate bits, apply a function over the words, etc). The compiler inlines aggressively, so the functor layer goes away.

For Jim, here is an article about function objects, http://www.codeguru.com/cpp/cpp/cpp_mfc/stl/article.php/c11449/

For Brian, when you said Marcus, I think you meant Marius, right

Corrected.