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cexternfunction-declaration

What is the meaning/significance of explicit "extern" keyword in function declaration?

Please explain why it uses extern in function declaration?

main.c

...
pthread_create(&displayThread, &attr, displayThrFxn, &displayEnv);
...

display.h

extern Void *displayThrFxn(Void *arg);

Why extern?

display.c

...
Void *displayThrFxn(Void *arg)
{
    // some code
}
...
Solution

  • The use of extern here is kind of redundant. By default, if nothing is specified, functions have external linkage.

    Quoting C11 standard, chapter §6.2.3

    If the declaration of an identifier for a function has no storage-class specifier, its linkage is determined exactly as if it were declared with the storage-class specifier extern. [...]