Integer atoms differ from string atoms as follows:

• Integer atoms are values from 0x0001 through 0xBFFF. The values of integer atoms and string atoms do not overlap, so the two types of atoms can be intermixed.

• The string representation of an integer atom is ddddd, where ddddd are decimal digits. Leading zeros are ignored.

• There is no usage count nor storage overhead associated with an integer atom.

The operating system uses integer atoms to detect whether the same window class name is being defined more than once. The system defines the predefined window class names using integer atoms as constants. When an application registers a window class, the system enters the specified class name in the system atom table. The system then compares the resultant atom with the predefined window-class constants and with the atoms representing the application-defined class names registered earlier. To be able to do this comparison, the system must express the preregistered class names as atoms. By defining the class names as integer atoms, the system ensures that the atoms do not conflict with the string atoms it generates for application-defined class names.