C 11?? ?????? ??? ?? extern ??? ??

extern ???? ???? ?? ??? ???? ???? ?????? ??? ? ?? ??? ??? C 11 ??????. . ?? ?? ?? ??? ?? ?? ????? ???? ??? ???? ??????? ??? ???? ??? ??? ???? ??? ?????? ??? ? ?? ??? ? ????.

?? ???

?? ???? ??, extern ???? ??? ?? ??? ?????? ???? ?? ?? ?? ? ????? ?? ???? ??????? ??? ???? ? ??? ? ????. ?? ?? ??????.

// header.h
template<typename T>
void ReallyBigFunction() {
    // Body
}

// source1.cpp
#include "header.h"
void something1() {
    ReallyBigFunction<int>();
}

// source2.cpp
#include "header.h"
extern template void ReallyBigFunction<int>();
void something2() {
    ReallyBigFunction<int>();
}

extern ???? ??? ????? RealBigFunction source1.cpp? source2.cpp ??? ??? ?? ?? ??? ?????.

source1.o
    void something1()
    void ReallyBigFunction<int>()    // Compiled first time

source2.o
    void something2()
    void ReallyBigFunction<int>()    // Compiled second time

??? ??? ?? ???? RealBigFunction ???? ??? ??? ?? ?? ??? ?????.

? ??? ????? source2.cpp?? extern ???? ??? ? ????.

// source2.cpp
#include "header.h"
extern template void ReallyBigFunction<int>();
void something2() {
    ReallyBigFunction<int>();
}

??? ?? ??? ?? ?? ??? ?????.

source1.o
    void something1()
    void ReallyBigFunction<int>() // Compiled just one time

source2.o
    void something2()
    // No ReallyBigFunction<int> here because of the extern

??? ?? ??? ???? ? ?? ?? ??? ? ?? ?? ??? ??? ???? ?? ??? ??? ??? ????.

??? ???

?? ???? ??? ???? ?? ???? ?? ??? ??? ?????? ??? ?? ????. ?? ?? ??? ????.

// header.h
template<typename T>
class Foo {
public:
    T f();
};

// source1.cpp
#include "header.h"
Foo<int> foo1;

// source2.cpp
#include "header.h"
extern template class Foo<int>;
Foo<int> foo2;

extern ???? ??? ????? Foo? ?? ?? ?? f? ??????. source1.cpp? source2.cpp ???? ??? ??? ?????. extern ???? ???? ?? ??? ? ?? ??????.

??

extern ???? C 11 ?????? ?? ??? ??? ??? ??? ??? ? ??? ?????. ???? ??? ?????? ???? ?? ????? extern ???? ?????? ???? ?? ??? ???? ? ????.

? ??? C 11? 'extern template'? ??? ?? ??? ?????? ???? ??? ??? ??? ? ?????? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!