模板类,朋友操作符<超载 [英] template class, friend operator << overload
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问题描述
我尝试重载<<运算符用于模板类。我有一个.h文件中的类的定义和它在.cpp文件中的实现。
I'm trying to overload the "<<" operator for a template class. I've the definition of the class in a .h file and its implementation in a .cpp file.
/tmp/ccjJIJhO.o: In function `main':
main.cpp:(.text+0xad): undefined reference to `std::basic_istream<char, std::char_traits<char> >& operator>><int>(std::basic_istream<char, std::char_traits<char> >&, FeatureVector<int>&)'
main.cpp:(.text+0xba): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& operator<< <int>(std::basic_ostream<char, std::char_traits<char> >&, FeatureVector<int> const&)'
collect2: ld returned 1 exit status
类定义:
#include <iostream>
using namespace std;
featurevector.h
featurevector.h
#ifndef FEATURE_VECTOR_H
#define FEATURE_VECTOR_H
#include <common.h>
template < class FEAT_TYPE >
class FeatureVector;
template < class FEAT_TYPE >
istream & operator >> (istream &, FeatureVector<FEAT_TYPE> &);
template < class FEAT_TYPE >
ostream & operator << (ostream &, const FeatureVector<FEAT_TYPE> &);
template < class FEAT_TYPE >
class FeatureVector{
public:
FeatureVector(int = 0);
...
friend istream & operator >> <>(istream &, FeatureVector<FEAT_TYPE> & );
friend ostream & operator << <>(ostream &, const FeatureVector<FEAT_TYPE> &);
...
~FeatureVector();
private:
int m_nDim;
FEAT_TYPE * m_pFeat;
};
#endif
featurevector.cpp
featurevector.cpp
#include <featurevector.h>
...
template < class FEAT_TYPE >
istream & operator >> (istream & input, FeatureVector< FEAT_TYPE> & refFeat ){
int d;
for(d=0; d < refFeat.getDim(); d++){
input >> refFeat.m_pFeat[d];
}
return (input);
}
template < class FEAT_TYPE >
ostream & operator << (ostream & output, const FeatureVector< FEAT_TYPE > & refFeat ){
int d;
for(d=0; d < refFeat.getDim(); d++){
output << refFeat.m_pFeat[d] << " ";
}
output << endl;
return (output);
}
...
#include "featurevector-impl.cpp"
$ b b
featurevector-impl.cpp
featurevector-impl.cpp
template class FeatureVector<int>;
//template istream & operator >> <>(istream &, FeatureVector<int> &);
//template ostream & operator << <>(ostream &, const FeatureVector<int> &);
mylib.h
mylib.h
#ifndef MY_LIB_H
#define MY_LIB_H
#include <featurevector.h>
#endif
main.cpp
main.cpp
#include <mylib.h>
#include <common.h>
int main(){
FeatureVector<int> pFeat(10);
cin >> (pFeat);
cout << (pFeat);
return (0);
}
与mylib相关联的Makefile
Makefile associated with "mylib"
INC=./inc
SRC=./src
LIB=./lib
OBJ=./obj
CC=g++
CFLAGS=-O3 -Wall
mylib: $(LIB)/mylib.a
echo "mylib was created!..."
$(LIB)/mylib.a: \
$(OBJ)/featurevector.o
ar csr $(LIB)/mylib.a \
$(OBJ)/featurevector.o
$(OBJ)/featurevector.o: $(SRC)/featurevector.cpp
$(CC) -c $(CFLAGS) $(SRC)/featurevector.cpp -I$(INC) \
-o $(OBJ)/featurevector.o
clean:
rm -rf $(LIB)/*.a
rm -rf $(OBJ)/*.o
main的Makefile。 cpp(main.cpp及其Makefile位于app目录下)
Makefile for main.cpp (the main.cpp with its Makefile are under an "app" directory)
LIB=../lib
INC=../inc
OBJ=../obj
BIN=../bin
CC=g++
CFLAGS=-O3 -Wall
LFLAGS=-lmylib -lm
$@.cpp: $(LIB)/mylib.a $@.cpp
cd ..; make; cd app;
$(CC) $(CFLAGS) $@.cpp -o $(BIN)/$@ -I$(INC) -L$(LIB) $(LFLAGS)
clean:
rm -rf $(BIN)/*
推荐答案
根据此,您必须将功能称为模板,在您的类定义。
According to this, you have to make the function known as template in your class definition.
class.h
#include <iostream>
using std::ostream;
template <typename T>
class A {
public:
...
template <typename J> // <-- CAUTION!
friend ostream &operator<<(ostream &output, const A<J> &a);
};
class.cpp
#include "class.h"
...
template <typename T>
ostream &operator<<(ostream &output, const A<T> &a) {
// Your implementation
return output;
}
...
template ostream &operator<<(ostream &output, const A<int> &a);
template ostream &operator<<(ostream &output, const A<float> &a);
如果行 template< typename J>
被删除,编译错误underfined reference。
If the line template <typename J>
is removed, the compilation error "underfined reference" comes.
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