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Tip of the Day
Language: C++
Expertise: All
Aug 11, 2000



Building the Right Environment to Support AI, Machine Learning and Deep Learning

Functions Are Extern by Default

Unless explicitly declared static, an ordinary function is implicitly declared extern in C and C++. For example:

extern void func(int i); // extern is redundant

However, sometimes the extern qualifier is added to a function declaration to document the fact that it has external linkage and can be called from any module, or source file, for example:

// from <string.h>
extern size_t strlen(const char * s); 

Do not confuse plain extern with extern "C"—the latter has a special meaning, i.e., the identifier has C linkage rather than C++ linkage.

Danny Kalev
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