c++ - 如何在C++中重载<<<用于 vector 的运算符

Question

我为C++中的运算符重载制作了以下最小示例。我想按如下所示打印 vector 。

#include <iostream>
#include <vector>

using namespace std;

ostream& operator<< (ostream& out, const vector<int>& v) {
        for(size_t i = 0; i < v.size(); i++) {
                out << v[i] << " ";
        }
        return out;
}

int main(void)
{
        vector<int> i = {1, 2};
        cout << i << endl;
}

但是，如果我使用以下版本将gcc作为 gcc test.cpp进行编译。

$ gcc --version
gcc (Arch Linux 9.3.0-1) 9.3.0

我到处都收到错误消息，似乎减少到以下情况。

undefined reference to `std::ostream::operator<<(int)'

但是为了完整起见，这里是完整的错误消息。

/usr/bin/ld: /tmp/cc8gPHc3.o: in function `operator<<(std::ostream&, std::vector<int, std::allocator<int> > const&)':
test.cpp:(.text+0x4e): undefined reference to `std::ostream::operator<<(int)'
/usr/bin/ld: test.cpp:(.text+0x5d): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)'
/usr/bin/ld: /tmp/cc8gPHc3.o: in function `main':
test.cpp:(.text+0xec): undefined reference to `std::cout'
/usr/bin/ld: test.cpp:(.text+0xfb): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::endl<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&)'
/usr/bin/ld: test.cpp:(.text+0x106): undefined reference to `std::ostream::operator<<(std::ostream& (*)(std::ostream&))'
/usr/bin/ld: /tmp/cc8gPHc3.o: in function `__static_initialization_and_destruction_0(int, int)':
test.cpp:(.text+0x195): undefined reference to `std::ios_base::Init::Init()'
/usr/bin/ld: test.cpp:(.text+0x1aa): undefined reference to `std::ios_base::Init::~Init()'
/usr/bin/ld: /tmp/cc8gPHc3.o: in function `std::vector<int, std::allocator<int> >::_S_check_init_len(unsigned long, std::allocator<int> const&)':
test.cpp:(.text._ZNSt6vectorIiSaIiEE17_S_check_init_lenEmRKS0_[_ZNSt6vectorIiSaIiEE17_S_check_init_lenEmRKS0_]+0x5e): undefined reference to `std::__throw_length_error(char const*)'
/usr/bin/ld: /tmp/cc8gPHc3.o: in function `__gnu_cxx::new_allocator<int>::deallocate(int*, unsigned long)':
test.cpp:(.text._ZN9__gnu_cxx13new_allocatorIiE10deallocateEPim[_ZN9__gnu_cxx13new_allocatorIiE10deallocateEPim]+0x1c): undefined reference to `operator delete(void*)'
/usr/bin/ld: /tmp/cc8gPHc3.o: in function `__gnu_cxx::new_allocator<int>::allocate(unsigned long, void const*)':
test.cpp:(.text._ZN9__gnu_cxx13new_allocatorIiE8allocateEmPKv[_ZN9__gnu_cxx13new_allocatorIiE8allocateEmPKv]+0x2c): undefined reference to `std::__throw_bad_alloc()'
/usr/bin/ld: test.cpp:(.text._ZN9__gnu_cxx13new_allocatorIiE8allocateEmPKv[_ZN9__gnu_cxx13new_allocatorIiE8allocateEmPKv]+0x3c): undefined reference to `operator new(unsigned long)'
/usr/bin/ld: /tmp/cc8gPHc3.o:(.data.rel.local.DW.ref.__gxx_personality_v0[DW.ref.__gxx_personality_v0]+0x0): undefined reference to `__gxx_personality_v0'
collect2: error: ld returned 1 exit status

Answer 1

使用g++而不是gcc解决了此问题。