ABL electronic PIC Microcontrollers PIC18 User Manual

Page of 312
External Linkage Rule:
1. names having file scope, that do not comply to any of previously stated internal 
linkage rules, have external linkage.
The storage class specifiers 
auto
and 
register
cannot appear in an external
declaration. For each identifier in a translation unit declared with internal linkage,
no more than one external definition can be given. An external definition is an
external declaration that also defines an object or function; that is, it also allocates
storage. If an identifier declared with external linkage is used in an expression
(other than as part of the operand of 
sizeof
), then exactly one external definition
of that identifier must be somewhere in the entire program.
mikroC allows later declarations of external names, such as arrays, structures, and
unions, to add information to earlier declarations. Here's an example:
int
a[];
// No size
struct
mystruct;
// Tag only, no member declarators
.
.
.
int
a[3] = {1, 2, 3};
// Supply size and initialize
struct
mystruct {
int
i, j;
};
// Add member declarators
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