C ++模板，未定义引用 [英] C++ templates, undefined reference

问题描述

我有一个函数声明如下：

  template< typename T& 
 T read（）; 
  

并定义如下：

  template< typename T> 
 T packetreader :: read（）{
 offset + = sizeof（T）; 
 return *（T *）（buf + offset-sizeof（T））;但是，当我尝试在我的main（）函数中使用它：
     / p> 
 
 
 数据包读取器; 
 reader.read< int>（）; 
  
我从g ++得到以下错误：
  g ++ -o main main.o packet.o 
 main.o：在main函数中：
 main.cpp :(。text + 0xcc）：未定义引用`int packetreader :: read< int>（）'
 collect2：ld返回1退出状态
 make：*** [main]错误1 
  
 
 
 
任何人都可以指向正确的方向？
解决方案
您需要使用 export 关键字。但是，我不认为G ++有适当的支持，所以你需要在标题中包含模板函数的定义，以便翻译单元可以使用它。这是因为尚未创建模板的< int> '版本'，只有< typename T> 'version。'
 
 
 
一个简单的方法是 #include  .cpp文件。然而，这可能导致问题，例如，当其他函数在.cpp文件中。它也可能会增加编译时间。
 
 
 
一个干净的方式是将你的模板函数移动到自己的.cpp文件中，并包含在标题 
 
 
 
  www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1426.pdf\">有关为什么应该尝试并在其头文件中放置模板函数定义的更多信息（并忽略 export ）。
 
I have a function declared like so:
template <typename T> 
T read();
and defined like so:
template <typename T>
T packetreader::read() {
    offset += sizeof(T);
    return *(T*)(buf+offset-sizeof(T)); 
}
However, when I try to use it in my main() function:
packetreader reader;
reader.read<int>();
I get the following error from g++:
g++ -o main main.o packet.o
main.o: In function `main':
main.cpp:(.text+0xcc): undefined reference to `int packetreader::read<int>()'
collect2: ld returned 1 exit status
make: *** [main] Error 1
Can anyone point me into the right direction?
解决方案
You need to use the export keyword. However, I don't think G++ has proper support, so you need to include the template function's definition in the header so the translation unit can use it.  This is because the <int> 'version' of the template hasn't been created, only the <typename T> 'version.'

An easy way is to #include the .cpp file.  However, this can cause problems, e.g. when other functions are in the .cpp file.  It will also likely increase the compile time.

A clean way is to move your template functions into its own .cpp file, and include that in the header or use the export keyword and compile it separately.

More information on why you should try and put template function definitions in its header file (and ignore export altogether).

                        
这篇关于C ++模板，未定义引用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！