模板类和自由函数名称空间的实现问题 [英] template class and free function namespace problems with implementation
问题描述
我有一个这样定义的类(琐碎的include和预处理器包装等被省略,但是它们在那里):
I have a class defined like this (trivial includes and preprocessor wrappers, etc. are omitted, but they are there):
In Matrix.h
namespace matrixmanip {
template<typename T>
class Matrix {
public:
void someFunc() const;
//...
};
template<typename T>
void Matrix<T>::someFunc() const {
//...
}
} // namespace matrixmanip
In bitTransform.h
#include "Matrix.h"
namespace matrixmanip {
Matrix<char> bitExpand(const Matrix<char> &mat);
} // namespace matrixmanip
In bitTransform.cpp
#include "bitTransform.h"
using namespace matrixmanip;
Matrix<char> bitExpand(const Matrix<char> &mat) {
mat.someFunc();
//...
}
In tester.cpp
#include "Matrix.h"
#include "bitTransform.h"
matrixmanip::Matrix<char> A ... // construct a character matrix, details of which are unimportant here
matrixmanip::Matrix<char> B = matrixmanip::bitExpand(A);
但是,当我这样编译和链接时:
However, when I compile and link like this:
g++ -c tester.cpp
g++ -c bitTransform.cpp
g++ -Wall -O2 tester.o bitTransform.o -o tester
我得到一个未定义的参考错误,
I get an undefined reference error, specifically
/tmp/ccateMEK.o: In function `main':
tester.cpp:(.text+0xbf9): undefined reference to `matrixmanip::bitExpand(matrixmanip::Matrix<char> const&)'
collect2: error: ld returned 1 exit status
为什么会出现此错误?在我看来,我的命名空间解析还可以,而且我的链接很好...
Why am I getting this error? It seems to me that my namespace resolution is okay and my linkage is fine...
推荐答案
bitExpand
在全局名称空间中定义自由函数,而不是在matrixmanip
名称空间中定义自由函数. using
指令不会将定义移到所使用的名称空间中.您应该将定义直接放在适当的名称空间中:
bitExpand
defines a free function in global namespace, not in matrixmanip
namespace. using
directive does not move definitions into the namespace being used. You should put definition in proper namespace directly:
namespace matrixmanip
{
Matrix<char> bitExpand(const Matrix<char> &mat)
{
mat.someFunc();
//...
}
}
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