AliWy

来源：MSDN 

The ICO File
An Icon file, which usually has the ICO extension, contains one icon resource. Given that an icon resource can contain multiple images, it is no surprise that the file begins with an icon directory:

typedef struct
{
    WORD           idReserved;   // Reserved (must be 0)
    WORD           idType;       // Resource Type (1 for icons)
    WORD           idCount;      // How many images?
    ICONDIRENTRY   idEntries[1]; // An entry for each image (idCount of 'em)
} ICONDIR, *LPICONDIR;
...