C++:架构错误的经典 undefined symbol

Question

最近在学习 C++，我在编译类时遇到了问题。我目前收到以下模糊的模板错误:

Undefined symbols for architecture x86_64:
  "SmallWorld::AJV::validate(nlohmann::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::adl_serializer>*, nlohmann::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::adl_serializer>*)", referenced from:
      SmallWorld::Map::(anonymous namespace)::readMap(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) in map.test.cpp.o
  "std::__1::function<unsigned long (SmallWorld::Map::Graph<SmallWorld::Region>)> SmallWorld::Map::algorithm::dfs<SmallWorld::Region>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::function<bool (std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::set<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::less<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > >&, std::__1::unordered_map<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::pair<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, std::__1::hash<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, std::__1::equal_to<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, std::__1::allocator<std::__1::pair<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const, std::__1::pair<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > > > const&)> const&)", referenced from:
      creates_a_connected_graph_small_world_map_Test::TestBody() in map.test.cpp.o
  "SmallWorld::Region::Region(nlohmann::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::adl_serializer>)", referenced from:
      std::__1::shared_ptr<SmallWorld::Region> std::__1::shared_ptr<SmallWorld::Region>::make_shared<nlohmann::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::adl_serializer> const&>(nlohmann::basic_json<std::__1::map, std::__1::vector, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, bool, long long, unsigned long long, double, std::__1::allocator, nlohmann::adl_serializer> const&&&) in map.test.cpp.o
ld: symbol(s) not found for architecture x86_64

可以简化为:

Undefined symbols for architecture x86_64:
  "SmallWorld::AJV::validate(nlohmann::json*, nlohmann::json*)", referenced from:
      SmallWorld::Map::(anonymous namespace)::readMap(string const&, string const&) in map.test.cpp.o
  "std::function<size_t(Graph<Region>)> SmallWorld::Map::algorithm::dfs<SmallWorld::Region>(string const&, std::function<bool (string const&, std::set<string> const&, std::unordered_map<string, string> const&)", referenced from:
      creates_a_connected_graph_small_world_map_Test::TestBody() in map.test.cpp.o
  "SmallWorld::Region::Region(nlohmann::json)", referenced from:
      std::shared_ptr<SmallWorld::Region> std::shared_ptr<SmallWorld::Region>::make_shared<nlohmann::json const&&&) in map.test.cpp.o
ld: symbol(s) not found for architecture x86_64

在我看来，这似乎是在说 AJV 类型上不存在方法 bool AJV::validate(json* schema, json* data)。但是我已经验证了常见的错误(与 header 声明不同的实现，与实现不同的调用)，但无济于事。

AJV 类的定义和实现如下:

// AJV.h
#ifndef SMALLWORLD_AJV_H
#define SMALLWORLD_AJV_H

#include <nlohmann/json.hpp>

using nlohmann::json;

namespace SmallWorld {
  class AJV {
  public:
    std::function<bool(json*)> compile(json* schema);
    bool validate(json* schema, json* data);
    json errors;
  private:
    json m_schema;
    std::function<bool(json*)> m_validator;
  };
};

#endif // SMALLWORLD_AJV_H

// AJV.cpp
#include <nlohmann/json.hpp>
#include "AJV.h"

using nlohmann::json;

namespace SmallWorld {
  std::function<bool(json*)> AJV::compile(json* schema) {
    return [](json* data){ return true; };
  };
  bool AJV::validate(json* schema, json* data){ return true; };
};

这是调用:

//loader.cpp
json* readMap(const string& map_path, const string& schema_path) {
        AJV ajv;
        json* schema = readJSONFile(schema_path);
        json* jmap = readJSONFile(map_path);
        if(ajv.validate(schema, jmap)){
          delete schema;
          return jmap;
        }else{
          delete schema;
          throw ajv.errors;
        }
      };

设置:

• 操作系统:MacOS 10.13.3
• C++版本:14
• 编译器: g++ => Apple LLVM 版本 9.0.0 (clang-900.0.39.2)
• 构建管理器:CMake 3.5.1
• IDE:Atom IDE w/linter-clang 用于 linting(不是真正的 IDE XD)

其他详细信息

编译通过命令行完成:mkdirp build && cd build && cmake .. && make

文件 AJV.h 位于指定包含路径的源代码树中。

我该如何解决这个问题？

干杯☀️

Answer 1

当您在 CMake 中注册一个项目时，您会同时列出头文件和源文件。然后它将针对您告诉它使用的相应 IDE/构建系统尽可能地处理这些问题。

如果你总是有一个头文件和一个 cpp 文件(没有要求；你可能会发现一些对象足够复杂/大到你想将它分成多个 cpp 文件以保持理智)那么你可以列出你的所有文件cmake 中没有扩展名的名称，并让它为您将 .cxx 和 .h 附加到末尾。这将使您只需输入一半内容。

作为替代方案，有一个不推荐的路线，即使用 file 命令扫描目录中的文件——但这仅在运行 cmake 时完成；因此不会自动更新；使得在一个系统上构建良好的源代码树成为可能；而不是另一个。