Unable to understand class definition in C++
<p>I am a newbie to disk-based R-trees although I have coded main memory based R-Trees. In order to understand disk based R-Trees I am using the library "libspatialIndex". While understanding the library I am coming across strange definitions of classes like the one given below:</p>

<pre><code>class SIDX_DLL IStorageManager
{
public:
    virtual void loadByteArray(const id_type id, uint32_t&amp; len, byte** data) = 0;
    virtual void storeByteArray(id_type&amp; id, const uint32_t len, const byte* const data) = 0;
    virtual void deleteByteArray(const id_type id) = 0;
    virtual ~IStorageManager() {}
}; // IStorageManager
</code></pre>

<p>I fail to understand this new definition of class whereby it uses SIDX_DLL in the class definition. Can someone please give me pointers as to what does SIDX_DLL represent in the class definition. </p>
