how to sort an array of objects?

[mrNoob]

sorry iam only coding for a month

i want to sort "personS" on there "score". how can i do this using
the code below ? ,, i keep having errors

class person
{
public:
person();
// etc...
private:
int age;
int score; // sort on score
// etc...
};

int main()
{
person *personS; // to be sorted
personS = new person[10];
sort(personS, personS+10, ??? ); // ? QUESTION HERE ?

return(1);
}

plz dont be too absract :/

 

[Thomas Matthews]

sorry iam only coding for a month

i want to sort "personS" on there "score". how can i do this using
the code below ? ,, i keep having errors

class person
{
public:
person();
// etc...

Add a function to compare two persons by score:
bool scored_less_than(const person& p} const
{return score < p.score;}
This function will be used below in sorting.

private:
int age;
int score; // sort on score
// etc...
};

Create a global function to compare two persons by age:
bool Person_Compare_By_Score(const person& p1,
const person& p2)
{
return p1.scored_less_than(p2);
}

int main()

You may want to be explicit:
int main(void)

{
person *personS; // to be sorted
personS = new person[10];
sort(personS, personS+10, ??? ); // ? QUESTION HERE ?

Pointers are not required here:
const unsigned int MAX_PERSONS = 10;
person personS[MAX_PERSONS];
/* Add code to initialize the persons */

/* Here is the code to sort by score: */
sort(personS, personS + MAX_PERSONS,
Person_Compare_By_Score);

The function is passed to the sort routine. See above.

return(1);

}

plz dont be too absract :/

Spell out your abbreviations. This will give others
a more educated opinion of you.

--
Thomas Matthews

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Other sites:
http://www.josuttis.com -- C++ STL Library book

 

[Aggro]

Add a function to compare two persons by score:
bool scored_less_than(const person& p} const

That should be:
bool scored_less_than(const person& p) const

And op also needs to include this:
#include <algorithm>


But I have also an extra question:
Can you do the same for items in std::vector, or do you have to convert
vector to some other format before sorting can be done?

Any recommendations how to do it?

 

[Mike Wahler]

That should be:
bool scored_less_than(const person& p) const

And op also needs to include this:
#include <algorithm>


But I have also an extra question:
Can you do the same for items in std::vector,

Yes. std::sort works with any container which supports
random access iterators (pointer types qualify as such,
that's why it works with arrays).

or do you have to convert
vector to some other format before sorting can be done?
No.


Any recommendations how to do it?

Pass iterators to the vector instead of array element addresses.

std::vector<person> pv;

/* (populate vector) */

std::sort(pv.begin(), pv.end(), Person_Compare_By_Score);

-Mike

 

[Mike Wahler]

You may want to be explicit:
int main(void)

Nit: In C++, empty parameter list
*means* no parameters (unlike C).

Also many consider the empty list more
idiomatic for C++.

YMMV.

-Mike

 

[Hardy]

oh, Mike, can you explain what the means of empty parameter in C? I just can
not tell the difference.

Thank you!

 

[Alex Vinokur]

sorry iam only coding for a month

i want to sort "personS" on there "score". how can i do this using
the code below ? ,, i keep having errors

class person
{
public:
person();
// etc...
private:
int age;
int score; // sort on score
// etc...
};

int main()
{
person *personS; // to be sorted
personS = new person[10];
sort(personS, personS+10, ??? ); // ? QUESTION HERE ?

return(1);
}

plz dont be too absract :/

Look at Appendix D.4 at
http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1487.pdf

 

[Karl Heinz Buchegger]

Nit: In C++, empty parameter list
*means* no parameters (unlike C).

In a function definition an empty parameter list
means the same thing in C and C++: no parameters.

In a function decalration (aka protoype) an empty
parameter list means different things in C++ and C

C++: no parameters
C : unknown number of parameters

 

[Mike Wahler]

oh, Mike, can you explain what the means of empty parameter in C? I just can
not tell the difference.

<C>
It means 'parameters not specified', whereas a
'void' parameter specifically means 'no parameters'.
</C>

In C++, a 'void' parameter and an empty parameter
list mean the same: no parameters.

-Mike