书上说"A const in C++ defaults to internal linkage; that is, it is visible only within the file where it is defined and cannot be seen at link time by other translation units."

我的程序如下

//file test.cpp is a file which defines a const int which should have internal linkage.
//test.cpp

const int i=60;

----------------------

//file main.cpp uses the const int defined in file test.cpp
//main.cpp

#include <iostream>
using namespace std;

extern const int i;

int main()
{
cout<<i<<endl;
}

上面的程序编译和运行都没有问题, 但是如果test.cpp中i的定义变成 static int i=60; main.cpp 中的声明变成extern int i; 编译错误显示变量i未定义。请问internal linkage的意义到底是什么?

[此贴子已经被作者于2007-9-25 11:57:51编辑过]

Thanks yuyunliuhen, however my question is why "const int i" which has internal linkage in test.cpp file can be accessed in main.cpp via "extern const int i" statement. My understanding is that because const int i has the internal linkage in test.cpp file, it can't be accessed in other files even use an extern modifier. So when compiling, compiler should generates an error shows that viriable i is undefined. But the fact is there is no error and program shows the value of i.

rgds/lori

My compiling environment is MinGW344. So, it seems that different environment with different result?

er....MinGW344 uses gcc version 3.4.4....however I will check documents and test myself. Thanks yuyunliuhen again.