Question

I was just wondering if treating an extern variable as the source buffer and passing it as an argument to strcpy() or any other function that can result in a buffer overflow is as unsafe and likely to result in buffer overflows as passing it an argument that came from an fgets() function with a specified limit higher than the size of the buffer.

Should special care be used with these extern variables or should they be treated no differently than any other variable?

Answer 1

extern only defines the linkage of an variable it does not change the variable in any other way.

Whether it is safe?

It is as safe/Unsafe as any other variable, the variable being declared extern has no bearing.
Using strcpy is as such Unsafe and may cause buffer overflows.
In C++ better option is to use std::string