在 C++ 中出现缺少 vtable 错误，导致“clang: error: linker command failed with exit code 1”

Question

我正在尝试研究c++中的接口和类。运行代码时，我收到缺少 vtable 的错误。我的完整代码是：

#include <iostream>

class IGPS{
public:
    virtual float getLatitude();
};

class MockGPS: public IGPS{
public:
    virtual float getLatitude() override;
};

float MockGPS::getLatitude(){
    return  11.3f;
}

void DriveRobot(IGPS& gps){
    float lat = gps.getLatitude();
    std::cout << "Lat : " << lat;
}

int main(int argc, const char * argv[]) {
    MockGPS gps;
    DriveRobot(gps);
    std::cout<< " Hello World! " << std::endl;
    
    return 0;
}

我得到的错误跟踪是

base ❯ clang main.cpp -std=c++11
Undefined symbols for architecture arm64:
  "std::__1::locale::use_facet(std::__1::locale::id&) const", referenced from:
      std::__1::ctype<char> const& std::__1::use_facet[abi:ue170006]<std::__1::ctype<char>>(std::__1::locale const&) in main-4b1700.o
  "std::__1::ios_base::getloc() const", referenced from:
      std::__1::basic_ios<char, std::__1::char_traits<char>>::widen[abi:ue170006](char) const in main-4b1700.o
  "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>::__init(unsigned long, char)", referenced from:
      std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>::basic_string[abi:ue170006](unsigned long, char) in main-4b1700.o
  "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>::~basic_string()", referenced from:
      std::__1::ostreambuf_iterator<char, std::__1::char_traits<char>> std::__1::__pad_and_output[abi:ue170006]<char, std::__1::char_traits<char>>(std::__1::ostreambuf_iterator<char, std::__1::char_traits<char>>, char const*, char const*, char const*, std::__1::ios_base&, char) in main-4b1700.o
      std::__1::ostreambuf_iterator<char, std::__1::char_traits<char>> std::__1::__pad_and_output[abi:ue170006]<char, std::__1::char_traits<char>>(std::__1::ostreambuf_iterator<char, std::__1::char_traits<char>>, char const*, char const*, char const*, std::__1::ios_base&, char) in main-4b1700.o
  "std::__1::basic_ostream<char, std::__1::char_traits<char>>::put(char)", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char>>& std::__1::endl[abi:ue170006]<char, std::__1::char_traits<char>>(std::__1::basic_ostream<char, std::__1::char_traits<char>>&) in main-4b1700.o
  "std::__1::basic_ostream<char, std::__1::char_traits<char>>::flush()", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char>>& std::__1::endl[abi:ue170006]<char, std::__1::char_traits<char>>(std::__1::basic_ostream<char, std::__1::char_traits<char>>&) in main-4b1700.o
  "std::__1::basic_ostream<char, std::__1::char_traits<char>>::sentry::sentry(std::__1::basic_ostream<char, std::__1::char_traits<char>>&)", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char>>& std::__1::__put_character_sequence[abi:ue170006]<char, std::__1::char_traits<char>>(std::__1::basic_ostream<char, std::__1::char_traits<char>>&, char const*, unsigned long) in main-4b1700.o
  "std::__1::basic_ostream<char, std::__1::char_traits<char>>::sentry::~sentry()", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char>>& std::__1::__put_character_sequence[abi:ue170006]<char, std::__1::char_traits<char>>(std::__1::basic_ostream<char, std::__1::char_traits<char>>&, char const*, unsigned long) in main-4b1700.o
      std::__1::basic_ostream<char, std::__1::char_traits<char>>& std::__1::__put_character_sequence[abi:ue170006]<char, std::__1::char_traits<char>>(std::__1::basic_ostream<char, std::__1::char_traits<char>>&, char const*, unsigned long) in main-4b1700.o
  "std::__1::basic_ostream<char, std::__1::char_traits<char>>::operator<<(float)", referenced from:
      DriveRobot(IGPS&) in main-4b1700.o
  "std::__1::cout", referenced from:
      DriveRobot(IGPS&) in main-4b1700.o
      _main in main-4b1700.o
  "std::__1::ctype<char>::id", referenced from:
      std::__1::ctype<char> const& std::__1::use_facet[abi:ue170006]<std::__1::ctype<char>>(std::__1::locale const&) in main-4b1700.o
  "std::__1::locale::~locale()", referenced from:
      std::__1::basic_ios<char, std::__1::char_traits<char>>::widen[abi:ue170006](char) const in main-4b1700.o
      std::__1::basic_ios<char, std::__1::char_traits<char>>::widen[abi:ue170006](char) const in main-4b1700.o
  "std::__1::ios_base::__set_badbit_and_consider_rethrow()", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char>>& std::__1::__put_character_sequence[abi:ue170006]<char, std::__1::char_traits<char>>(std::__1::basic_ostream<char, std::__1::char_traits<char>>&, char const*, unsigned long) in main-4b1700.o
  "std::__1::ios_base::clear(unsigned int)", referenced from:
      std::__1::ios_base::setstate[abi:ue170006](unsigned int) in main-4b1700.o
  "std::terminate()", referenced from:
      ___clang_call_terminate in main-4b1700.o
  "typeinfo for IGPS", referenced from:
      typeinfo for MockGPS in main-4b1700.o
  "vtable for IGPS", referenced from:
      IGPS::IGPS() in main-4b1700.o
   NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "vtable for __cxxabiv1::__si_class_type_info", referenced from:
      typeinfo for MockGPS in main-4b1700.o
   NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "___cxa_begin_catch", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char>>& std::__1::__put_character_sequence[abi:ue170006]<char, std::__1::char_traits<char>>(std::__1::basic_ostream<char, std::__1::char_traits<char>>&, char const*, unsigned long) in main-4b1700.o
      ___clang_call_terminate in main-4b1700.o
  "___cxa_end_catch", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char>>& std::__1::__put_character_sequence[abi:ue170006]<char, std::__1::char_traits<char>>(std::__1::basic_ostream<char, std::__1::char_traits<char>>&, char const*, unsigned long) in main-4b1700.o
      std::__1::basic_ostream<char, std::__1::char_traits<char>>& std::__1::__put_character_sequence[abi:ue170006]<char, std::__1::char_traits<char>>(std::__1::basic_ostream<char, std::__1::char_traits<char>>&, char const*, unsigned long) in main-4b1700.o
  "___gxx_personality_v0", referenced from:
      /private/var/folders/x9/hk8k3w4s6yl4hp1jbgk4qc680000gn/T/main-4b1700.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

我能理解的主要错误是：

NOTE: a missing vtable usually means the first non-inline virtual member function has no definition. 

有关如何解决此错误的任何建议。 问候

我正在尝试学习c++中的接口和类。 我尝试在函数定义中添加大括号，例如

virtual float getLatitude() {};

或

virtual float getLatitude(){} override;

按照某些网站的建议，但它给出“非空函数不返回值”语法错误。 我使用 Xcode v15.3 进行编程。我的 clang 版本是 15.0.0

Answer 1

你实际上有两个问题。

第一个是你使用

clang

来构建。该程序用于构建C程序。对于 C++，请使用

clang++

。大多数错误其实都是由此而来。

第二个问题，即标题中提到的问题，是典型的当您有一个未定义（实现）的非抽象虚函数时。

在你的情况下，它是

IGPS::getLatitude

功能。要么定义它

virtual float getLatitude() { return 0.0f; }

或将其标记为摘要

virtual float getLatitude() = 0;

---

完全不同的一点是，除非您有非常具体的要求，否则不要使用

float

。使用

double

。