全部。
我制作了一组c++代码如下。
然后，我通过 g++ 将每个编译成功.cpp。
但是，我得到了一个链接错误.o
Undefined symbols for architecture x86_64:
"derive1<3>::derive1(int)", referenced from:
derive2::derive2(int)in derive2.o
derive2::derive2(int)in derive2.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status
你能告诉我发生了什么事吗？如果我将所有代码片段绑定在一个文件中，则不会出现任何错误，并且可以按我的预期完美运行。我想我应该在某处引入 extern 关键字，但我不知道该怎么做。
我的编译器是
i686-apple-darwin11-llvm-g++-4.2 (GCC) 4.2.1（基于 Apple Inc. build 5658）（LLVM build 2336.11.00）
“基地.hpp”
class base {
public:
virtual int hoge( int num ) = 0;
};
“派生1.hpp”
#include "base.hpp"
#include <iostream>
template <int N>
class derive1 : public base {
public:
explicit derive1( int n );
virtual int hoge( int num ) {
std::cout << "num = " << num << std::endl
<< "N = " << N << std::endl;
return N;
}
};
“派生1.cpp”
#include "derive1.hpp"
template <int N>
derive1<N>::derive1 ( int n ) {
std::cout << "This is the constructer of derive1" << std::endl
<< "N = " << N << ", n = " << n << std::endl;
}
“派生2.hpp”
#include "derive1.hpp"
#include <iostream>
class derive2 : public derive1<3> {
public:
explicit derive2( int n );
};
“派生2.cpp”
#include "derive2.hpp"
derive2::derive2( int n ) : derive1<3>( n ) {
std::cout << "This is the constructer of derive2" << std::endl
<< "n = " << n << std::endl;
}
“派生测试.cpp”
#include<iostream>
#include "derive2.hpp"
int main() {
derive2 test(3);
std::cout << "return value = "
<< test.hoge( 5 )
<< std::endl;
return 0;
}