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//main.cpp

#include "func.h"

int main()
{
  func();
}


//func.h

void func();


//func.cpp

#include "func.h"
#include <stdio.h>

void func()
{
    printf("Hello world\n");
}


±àÒë g++ -o main main.cpp

Ìáʾ undifined reference to "func()"

---

//func.h

extern void func();

---

ÁíÍâµÃд¸ömakefile£¬ÏȱàÒëfun.cpp

---

C/C++ code:


// main.h
extern void func();

//main.cpp
#include "main.h"

int main()
{
func();
}

//func.h
void func();


//func.cpp
#include "func.h"
#include <stdio.h>

void func()
{
printf("Hello world\n");
}

---

g++ -o main main.cpp func.h func.cpp
±àÒëʱÕâÑù±àÒë¾Í¿ÉÒÔÁË

---

extern ¼ÓÁË

g++ -o func.o -c func.cpp
g++ -o main main.cpp

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---

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extern Ëƺõ¼Ó²»¼ÓÓ¦¸ÃÎÞËùν£¬·´ÕýĬÈÏÊÇÍⲿ¡£

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±àÒëÆ÷µÄ²î±ð»¹ÊǺܴóµÄ°¡¡£

---

g++ -o main main.cpp func.cpp
./main