This section describes options for using code not written in IDL. It contains the following topics.

Techniques That Do Not Use IDL’s Internal API

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This section discusses techniques that allow IDL to work together with programs written in other programming languages, using IDL’s “public” interfaces. Little or no familiarity with IDL’s internal interfaces is required. For many users, the techniques in this section will solve most problems that require IDL to use, or be used by, other programs. Topics covered include:

• Using SPAWN and Pipes
• Using CALL_EXTERNAL
• Remote Procedure Calls

IDL’s Internal API

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This section describes IDL’s internal implementation in enough detail to allow you to write an IDL system routine in another compiled programming language (usually C) and link it with IDL. Topics covered include:

• Types
• Keyword Processing
• Variables
• String Processing
• Error Handling
• Type Conversion
• UNIX Signals
• Timers
• Files and I/O
• Miscellaneous Topics

Techniques That Use IDL’s Internal API

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This section describes the process of combining IDL with code written in another programming language. Topics covered include:

• Adding System Routines
• Callable IDL
• Adding External Widgets to IDL
• Obsolete Internal Interfaces