External Variables and use extern to access it

Created: 2022-08-15
Tags: #fleeting

int num = 1;  // This is an external variable

int main() {
    extern int num; // Use `extern` to access external variable
    printf("%i", num);
}
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Useful for readability ( if external variable is in source file)
Useful when external variable is outside the source file, like file1, file2 and merge together.
Usual practice is to collect extern declarations of variables/functions in a separate file, historically called a header.h,
that is included by #include at the front of each source file.

If the external variable is inside the source file itself.
We can omit the extern declaration, specifically -> extern int num
But for readability purposes, put an extern to an external variable