Sorting a list with class for complex types [modified]

[David Crow]

Isn't the third parameter of sort() a (pointer to a) comparison routine?

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"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

[Jun Du]

Assuming that the length of Sequence is stored in Length, you can provide your own comparison function, which compares Length data between any two list items. Best, Jun

[FarPointer]

you can find it here :- http://www.codeguru.com/forum/showthread.php?t=366063[^] Check this one also :- http://www.codeproject.com/vcpp/stl/functor.asp[^] Regards, FarPointer Blog:FARPOINTER -- modified at 12:49 Monday 10th July, 2006

[Harold_Wishes]

This program for the first link is not compiling and it is hard to see where the sort is taking place. I will check the other link. -- modified at 13:04 Monday 10th July, 2006

[FarPointer]

Well the other link is for vector you need to customize it, i feel that we need to customize it for list. sort void sort(); Sorts the list elements in ascending order. The comparison operator < ("less than") must be defined for the list element type. Note that the STL sort algorithm does NOT work for lists; that's why a sort member function is supplied. nums.sort(); If we provide the < than operator for the struct its fine i guess. Regards, FarPointer Blog:FARPOINTER -- modified at 13:34 Monday 10th July, 2006

[Harold_Wishes]

The second link contains a good example. They are using the <vector> class. I am using the <list> class to store my list. I suppose I can use the vector example to implement what I am trying to do with the <list> class. I will have to think about this because I do not think items in lists can be accessed at random like vectors. Perhaps I am wrong on both accounts. :^) Regards again. HRW -- modified at 13:36 Monday 10th July, 2006

[David Crow]

Harold_Wishes wrote:

This program for the first link is not compiling...

Why not? What compiler error are you receiving?

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"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

[FarPointer]

try overiding the < operator of the struct. Chosing between vector and list you need to be careful bcoz the vector reallocates the whole data on push_back if it doesnt has space to expand ,while list is a linked list .so u need to choose according to your ease. just bcoz you cant do sort on it doesnt mean we have to drop it , you can also write sort from scratch. Regards, FarPointer Blog:FARPOINTER

[Harold_Wishes]

Well, I hate to place it here, but there were 14 errors. :omg: C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(23) : error C2955: 'list' : use of class template requires template argument list c:\program files\microsoft visual studio\vc98\include\list(415) : see declaration of 'list' C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(23) : error C2133: 'mylist' : unknown size C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(23) : error C2512: 'list' : no appropriate default constructor available C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(23) : error C2262: 'mylist' : cannot be destroyed C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(28) : error C2662: 'push_back' : cannot convert 'this' pointer from 'class std::list' to 'class std::list<_Ty,_A> &' Reason: cannot convert from 'class std::list' to 'class std::list<_Ty,_A>' Conversion requires a second user-defined-conversion operator or constructor C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(30) : error C2662: 'push_back' : cannot convert 'this' pointer from 'class std::list' to 'class std::list<_Ty,_A> &' Reason: cannot convert from 'class std::list' to 'class std::list<_Ty,_A>' Conversion requires a second user-defined-conversion operator or constructor C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(33) : error C2663: 'sort' : 2 overloads have no legal conversion for 'this' pointer C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(36) : error C2955: 'list' : use of class template requires template argument list c:\program files\microsoft visual studio\vc98\include\list(415) : see declaration of 'list' C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(36) : error C2955: 'list' : use of class template requires template argument list c:\program files\microsoft visual studio\vc98\include\list(415) : see declaration of 'list' C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(36) : error C2663: 'begin' : 2 overloads have no legal conversion for 'this' pointer C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(36) : error C2512: 'const_iterator' : no appropriate default constructor available C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(36) : error C2262: 'citer' : c

[FarPointer]

Make it list<"MyData"> mylist; Remove the qoutes :) It will work. Regards, FarPointer Blog:FARPOINTER -- modified at 13:54 Monday 10th July, 2006

[Harold_Wishes]

I still could not get it to run. :confused: C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(33) : error C2664: 'void __thiscall std::list >::sort(struct std::greater)' : cannot convert parameter 1 from ' bool (const class MyData &,const class MyData &)' to 'struct std::greater' No constructor could take the source type, or constructor overload resolution was ambiguous C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(36) : error C2955: 'list' : use of class template requires template argument list c:\program files\microsoft visual studio\vc98\include\list(415) : see declaration of 'list' C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(36) : error C2955: 'list' : use of class template requires template argument list c:\program files\microsoft visual studio\vc98\include\list(415) : see declaration of 'list' C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(36) : error C2440: 'initializing' : cannot convert from 'class std::list >::iterator' to 'class std::list<_Ty,_A>::const_iter ator' No constructor could take the source type, or constructor overload resolution was ambiguous C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(36) : error C2262: 'citer' : cannot be destroyed C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(37) : error C2679: binary '!=' : no operator defined which takes a right-hand operand of type 'class std::list >::iterator' ( or there is no acceptable conversion) C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(39) : error C2228: left of '.m_iData' must have class/struct/union type Error executing cl.exe. Sort.exe - 7 error(s), 0 warning(s)

#include <list>
#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
list<MyData> mylist;

// Add data to the list
MyData data;
data.m_iData = 3;
mylist.push_back(data);
data.m_iData = 1;
mylist.push_back(data);

// Sort the list using predic

[David Crow]

Gotta watch those angle brackets:

void main( void )
{
// Create list
list<MyData> mylist;
...
for (list<MyData>::const_iterator citer = mylist.begin();
}

---

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

[FarPointer]

Change it in the for loop also . Regards, FarPointer Blog:FARPOINTER

[FarPointer]

how did u bring those mydata in-side the angular brackets . and that horizontal slash in prev post. Regards, FarPointer Blog:FARPOINTER

[Harold_Wishes]

I decided to pick this apart and comment out the for loop because it is still not obvious to me where the problem is. The for loop seems to declare a pointer and initialize it to point to the beginning of the list and simply prints each item on screen until the pointer reaches the end. That aside I notice there appears to be some conversion type error in the line above with mylist.sort(MyDataSortPredicate); See error message below. :sigh: c:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(33) : error C2664: 'void __thiscall std::list >::sort(struct std::greater)' : cannot convert parameter 1 from ' bool (const class MyData &,const class MyData &)' to 'struct std::greater' No constructor could take the source type, or constructor overload resolution was ambiguous Error executing cl.exe. Sort.exe - 1 error(s), 0 warning(s)

mylist.sort(MyDataSortPredicate);

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

[David Crow]

FarPointer wrote:

and that horizontal slash in prev post.

Horizontal rule.

---

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

[Zac Howland]

Harold_Wishes wrote:

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

Don't write your own loop for this.

// declared somewhere
void printData(const MyData& data)
{
	cout << data.m_iData << endl;
}

// use instead of loop
for_each(myList.begin(), myList.end(), printData);

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week Zac

[Harold_Wishes]

This worked. But I still have commented out the code that is suppose to do the sort---> mylist.sort(MyDataSortPredicate);

C:\Documents and Settings\WoodallH\Desktop\C++\Project 6 Nesty tag\Sort.cpp(38) : error C2664: 'void __thiscall std::list<class MyData,class std::allocator<class MyData> >::sort(struct std::greater<class MyData>)' : cannot convert parameter 1 from '
bool (const class MyData &,const class MyData &)' to 'struct std::greater<class MyData>'
No constructor could take the source type, or constructor overload resolution was ambiguous
Error executing cl.exe.

-- modified at 15:03 Monday 10th July, 2006

[David Crow]

See here for the STL fix.

---

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

[Zac Howland]

You can either use the general sort algorithm (std::sort) or write a specialized less<MyData>() functor that looks something like:

struct std::less
{
	bool operator()(const MyData& lhs, const MyData& rhs)
	{
		return lhs.m_iData < rhs.m_iData;
	}
};

And then call mylist.sort(std::less<MyData>). If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week Zac