14.1: Extern Statement

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If a function is called from a source file and the function code is not located in the current source file, the assembler will generate an error. The same applies to variables accessed that are not located in the current file. In order to inform the assembler that the function code or variables are in another file, the extern statement is used. The syntax is as follows:

    extern     <symbolName>

The symbol name would be the name of the function or a variable that is located in a different source file. In general, using global variables accessed across multiple files is considered poor programming practice and should be used sparingly (if at all). Data is typically passed between functions as arguments for the function call.

The examples in the text focus on using external functions only with no globally declared variables.