使用标头中的构造函数初始化类

Question

i´m having this error. My header:

libtorrent::fingerprint a("LT", LIBTORRENT_VERSION_MAJOR, LIBTORRENT_VERSION_MINOR, 0, 0);
class TorrentClass
{
}

The compiler complains that libtorrent::fingerprint a already defined in another class, because it has been inclused. So i move it to inside my class

    class TorrentClass
    {
           private:
           libtorrent::fingerprint a("LT", LIBTORRENT_VERSION_MAJOR, LIBTORRENT_VERSION_MINOR, 0, 0);
    }

But then my compiler get very strange errors over that moved line, like

error C2059: syntax error : 'string'

What i´m doing wrong ?

Answer 1

You cannot do this in C++.

If you want an instance of libtorrent::fingerprint called a (terrible name) then you will need to declare it as an attribute of the class and initialise it in a constructor. Here is an example:

class TorrentClass
{
public:
    TorrentClass()
        :a("LT", LIBTORRENT_VERSION_MAJOR, LIBTORRENT_VERSION_MINOR, 0, 0)
    {
    }

private:
    libtorrent::fingerprint a
};

error C2059: syntax error : 'string'

This has nothing to do with the code that you posted.

Answer 2

In your .h file. Declare this:

#ifndef CLASS_TORRENT_H
#define CLASS_TORRENT_H
#include "libtorrent.h" // I'm guessing this is the header file that declares the "fingerprint" class
extern libtorrent::fingerprint a;
class TorrentClass
{
public:
   TorrentClass();
   // your class declaration goes here
};

#endif

In your .cpp (.cc) file. Define the objects:

#include "ClassTorrent.h" // the header file described above
libtorrent::fingerprint a("LT", LIBTORRENT_VERSION_MAJOR, LIBTORRENT_VERSION_MINOR, 0, 0);
TorrentClass::TorrentClass()
{
  // your constructor code goes here.
}

Also, on my team, we explicitly disallow "global objects" such as the instance of "a" you have declared. The reason being is that the constructor runs before "main" (in a non-deterministic order with all the other global objects). And it's destructor doesn't run until after main exits.

If you really need "a" to be global, instantiate it as a pointer and allocate it with new:

libtorrent::fingerprint *g_pFingerPrintA;
int main()
{
    g_pFingerPrintA = new libtorrent::fingerprint("LT", LIBTORRENT_VERSION_MAJOR, LIBTORRENT_VERSION_MINOR, 0, 0);

    // program code goes here

    // shutdown
    delete g_pFingerPrintA;
}