1.3.1 Clipboard Basics

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The system clipboard provided by modern operating systems allows users to transfer data of various formats between applications that are running on the same computer.

To copy data from one application to another, a user first places a selection of data onto the clipboard. This is called a "copy operation". The user then switches to another application and, after having navigated to an appropriate location within this application, the data is extracted from the clipboard and inserted into the target location. This is called a "paste" operation.

The copy and paste operations are two distinct actions and form the basis for clipboard manipulation. The copy operation always takes place before the paste operation to guarantee that the correct data is transferred. The passage of time between the copy and paste operations does not affect the outcome of the transfer of data.

System clipboards are not limited to holding one particular format of data at a given time. Instead, they provide the ability to store data of various formats simultaneously. For example, assume that a user has copied some text to the clipboard. The application that places the text onto the clipboard can place multiple formats of that text onto the clipboard, such as Unicode, ASCII 8, or a graphical image representation. This flexibility enables a wide spectrum of applications to extract data from the clipboard. For example, some applications might be able to manipulate only ASCII 8 text. By allowing both Unicode and ASCII 8 formats to coexist on the clipboard, ASCII 8-only applications can obtain text from applications that natively manipulate Unicode characters, but are flexible enough to place data onto the clipboard in a wider array of formats.

Basic programmatic access to the clipboard provided by an operating system usually ensures that any application has the ability to do the following:

  • Place data onto the clipboard.

  • Extract data from the clipboard.

  • Enumerate the data formats available on the clipboard.

  • Register to receive notifications when the system clipboard is updated.

Applications that leverage operating system-supplied clipboard functionality can share data seamlessly, provided that the data is of the appropriate format. Of course, if an application does not make use of system-supplied clipboard functionality, its ability to exchange data with other applications is constrained and limited to ad-hoc or proprietary mechanisms.