C++尝试将命名空间放在单独文件中时出现未定义符号。

huangapple
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英文:

C++ Undefined symbols when I try to put namespace in a separate file

问题

I have a problem with putting namespaces in separate files. Everything works for me when I write everything in one file, but when I try to create cpp+hpp files, that's where it all starts. Maybe I'm doing something wrong in the header file or linking the files incorrectly? I really don't know. I will be very grateful for your help.

Here is my error. On 86x_64 it also throws it out, but without mentioning the architecture:

  1. Undefined symbols for architecture arm64:
  2.   "Huffman::operator<<(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, Huffman::EncodingMap const&)", referenced from:
  3.       _main in main-4994c4.o
  4. ld: symbol(s) not found for architecture arm64
  1. // huffman.cpp
  2. #include <iostream>
  3. #include <string>
  4. #include <queue>
  5. #include <unordered_map>
  6. #include <memory>
  8. namespace Huffman
  9. {
  10.   // ... (code omitted for brevity)
  11. };
  1. // huffman.hpp
  2. #ifndef HUFFMAN_H
  3. #define HUFFMAN_H
  5. #include <iostream>
  6. #include <string>
  7. #include <queue>
  8. #include <unordered_map>
  9. #include <memory>
  11. namespace Huffman
  12. {
  13.   // ... (code omitted for brevity)
  14. };
  16. #endif
  1. // main.cpp
  2. #include <iostream>
  3. #include "./huffman.hpp"
  5. int main()
  6. {
  7.   auto [encoded, map] = Huffman::encode("hello world");
  8.   std::cout << encoded << std::endl;
  9.   std::cout << map << std::endl;
  11.   return 0;
  12. }

I tried to build it with cmake, but I also built it myself for testing, and the error is really independent of my build system:

  1. g++ ./src/main.cpp ./src/huffman.cpp -std=c++17

Is there anything specific you'd like to know or discuss regarding this code?

英文:

I have a problem with putting namespaces in separate files. Everything works for me when I write everything in one file, but when I try to create cpp+hpp files, that's where it all starts. Maybe I'm doing something wrong in the headerfile or linking the files incorrectly? I really don't know. I will be very grateful for your help.

Here is my error. On 86x_64 it also throws it out, but without mentioning the architecture

  1. Undefined symbols for architecture arm64:
  2.   &quot;Huffman::operator&lt;&lt;(std::__1::basic_ostream&lt;char, std::__1::char_traits&lt;char&gt; &gt;&amp;, Huffman::EncodingMap const&amp;)&quot;, referenced from:
  3.       _main in main-4994c4.o
  4. ld: symbol(s) not found for architecture arm64
  1. // huffman.cpp
  2. #include &lt;iostream&gt;
  3. #include &lt;string&gt;
  4. #include &lt;queue&gt;
  5. #include &lt;unordered_map&gt;
  6. #include &lt;memory&gt;
  8. namespace Huffman
  9. {
  10.   struct TreeNode
  11.   {
  12.   private:
  13.     struct Compare
  14.     {
  15.       bool operator()(std::shared_ptr&lt;TreeNode&gt; left, std::shared_ptr&lt;TreeNode&gt; right)
  16.       {
  17.         return left-&gt;frequency &gt; right-&gt;frequency;
  18.       }
  19.     };
  21.   public:
  22.     char symbol;
  23.     unsigned frequency;
  24.     std::shared_ptr&lt;TreeNode&gt; left;
  25.     std::shared_ptr&lt;TreeNode&gt; right;
  27.     TreeNode(char symbol, unsigned frequency)
  28.         : symbol(symbol), frequency(frequency) {}
  30.     static std::shared_ptr&lt;TreeNode&gt; buildTree(const std::string &amp;text)
  31.     {
  32.       std::unordered_map&lt;char, unsigned&gt; frequencyTable;
  33.       for (char c : text)
  34.       {
  35.         ++frequencyTable[c];
  36.       }
  38.       std::priority_queue&lt;std::shared_ptr&lt;TreeNode&gt;, std::vector&lt;std::shared_ptr&lt;TreeNode&gt;&gt;, Compare&gt; queue;
  40.       for (const auto &amp;[symbol, frequency] : frequencyTable)
  41.       {
  42.         queue.push(std::make_shared&lt;TreeNode&gt;(symbol, frequency));
  43.       }
  45.       while (queue.size() &gt; 1)
  46.       {
  47.         auto left = queue.top();
  48.         queue.pop();
  50.         auto right = queue.top();
  51.         queue.pop();
  53.         auto newNode = std::make_shared&lt;TreeNode&gt;(&#39;$&#39;, left-&gt;frequency + right-&gt;frequency);
  54.         newNode-&gt;left = left;
  55.         newNode-&gt;right = right;
  57.         queue.push(newNode);
  58.       }
  60.       return queue.top();
  61.     }
  62.   };
  64.   class EncodingMap
  65.   {
  66.   private:
  67.     std::unordered_map&lt;char, std::string&gt; map;
  69.     void build(std::shared_ptr&lt;Huffman::TreeNode&gt; node, std::string code)
  70.     {
  71.       if (node.get() == nullptr)
  72.         return;
  74.       if (node-&gt;left == nullptr &amp;&amp; node-&gt;right == nullptr)
  75.       {
  76.         map[node-&gt;symbol] = code;
  77.         return;
  78.       }
  80.       build(node-&gt;left, code + &quot;0&quot;);
  81.       build(node-&gt;right, code + &quot;1&quot;);
  82.     }
  84.   public:
  85.     EncodingMap(const std::string &amp;text)
  86.     {
  87.       auto root = TreeNode::buildTree(text);
  88.       build(root, &quot;&quot;);
  89.     }
  91.     friend std::ostream &amp;operator&lt;&lt;(std::ostream &amp;os, const EncodingMap &amp;map)
  92.     {
  93.       for (auto &amp;&amp;[key, value] : map.map)
  94.       {
  95.         std::cout &lt;&lt; key &lt;&lt; &quot;=&quot; &lt;&lt; value &lt;&lt; std::endl;
  96.       }
  97.       return os;
  98.     }
  100.     const std::string &amp;operator[](char symbol)
  101.     {
  102.       return map[symbol];
  103.     }
  104.   };
  106.   std::pair&lt;std::string, EncodingMap&gt; encode(const std::string &amp;text)
  107.   {
  108.     EncodingMap map = EncodingMap(text);
  110.     std::string encodedText;
  111.     for (char c : text)
  112.     {
  113.       encodedText += map[c];
  114.     }
  116.     return std::make_pair(encodedText, map);
  117.   }
  118. };
  1. // huffman.hpp
  2. #ifndef HUFFMAN_H
  3. #define HUFFMAN_H
  5. #include &lt;iostream&gt;
  6. #include &lt;string&gt;
  7. #include &lt;queue&gt;
  8. #include &lt;unordered_map&gt;
  9. #include &lt;memory&gt;
  11. namespace Huffman
  12. {
  13.   struct TreeNode
  14.   {
  15.   public:
  16.     char symbol;
  17.     unsigned frequency;
  18.     std::shared_ptr&lt;TreeNode&gt; left;
  19.     std::shared_ptr&lt;TreeNode&gt; right;
  21.     TreeNode(char symbol, unsigned frequency)
  22.         : symbol(symbol), frequency(frequency) {}
  24.     static std::shared_ptr&lt;TreeNode&gt; buildTree(const std::string &amp;text);
  25.   };
  27.   class EncodingMap
  28.   {
  29.   public:
  30.     EncodingMap(const std::string &amp;text);
  32.     friend std::ostream &amp;operator&lt;&lt;(std::ostream &amp;os, const EncodingMap &amp;map);
  34.     const std::string &amp;operator[](char symbol);
  35.   };
  37.   std::pair&lt;std::string, EncodingMap&gt; encode(const std::string &amp;text);
  38. };
  40. #endif
  1. // main.cpp
  2. #include &lt;iostream&gt;
  3. #include &quot;./huffman.hpp&quot;
  5. int main()
  6. {
  7.   auto [encoded, map] = Huffman::encode(&quot;hello world&quot;);
  8.   std::cout &lt;&lt; encoded &lt;&lt; std::endl;
  9.   std::cout &lt;&lt; map &lt;&lt; std::endl;
  11.   return 0;
  12. }

I tried to build it with cmake, but I also built it myself for testing, and the error is really independent of my build system.

  1. g++ ./src/main.cpp ./src/huffman.cpp -std=c++17

答案1

得分: 2

这就是你应该将类拆分为头文件和源文件的方式。

  1. // 头文件，x.h
  2. #ifndef X_H
  3. #define X_H
  4. class X
  5. {
  6. void f();
  7. };
  8. #endif
  9. // 源文件，x.cpp
  10. #include &quot;x.h&quot;
  11. void X::f()
  12. {
  13. // 此处编写代码
  14. }
英文:

This is how you are supposed to split classes into header file and source files

  1. // header file, x.h
  2. #ifndef X_H
  3. #define X_H
  4. class X
  5. {
  6. void f();
  7. };
  8. #endif
  9. // source file, x.cpp
  10. #include &quot;x.h&quot;
  11. void X::f()
  12. {
  13. // code here
  14. }

huangapple
  • 本文由 发表于 2023年5月17日 17:25:21
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