c++ - Undefined reference to template class destructor -

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• what undefined reference/unresolved external symbol error , how fix it? 27 answers

i had problem template class queue had been implementing functions in implementation file, saw this answer , resolved implementation in header file:

queue.hpp

#ifndef queue_hpp #define queue_hpp  #include "instruction.hpp" #include  "microblazeinstruction.hpp"  #include <memory> #include <list>  template<typename t> class queue{ public:     queue(unsigned int max): maxsize{max} {};     ~queue();      std::list<t> getqueue(){         return queue;     };      void push(t obj){         if(queue.size() < maxsize){             queue.push_front(obj);         }         else{             queue.pop_back();             queue.push_front(obj);         }     };  private:     queue(const queue&);     queue& operator=(const queue&);     unsigned int maxsize;     std::list<t> queue; };   #endif 

and call function main:

#include "icm/icmcpumanager.hpp" #include "instruction.hpp" #include "microblazeinstruction.hpp" #include "cpumanager.hpp" #include "file.hpp" #include "utils.hpp" #include "mbinstructiondecode.hpp" #include "queue.hpp" #include "patterndetector.hpp"  #include <iostream> #include <fstream> #include <string> #include <iomanip> #include <sstream> #include <cstdint> #include <memory>  int main(int argc, char *argv[]){     ...      // create pointer microblaze instruction     std::shared_ptr<microblazeinstruction> newmbinstruction;      // maximum pattern size     const unsigned int maxpatternsize = 300;      // creating queue     queue<std::shared_ptr<microblazeinstruction>> matchingqueue(maxpatternsize);          ... } 

and still have compilation error:

# linking platform faith.exe g++ ./cpumanager.o ./instruction.o ./file.o ./utils.o ./microblazeinstruction.o ./mbinstructiondecode.o ./patterndetector.o ./main.o -m32 -lc:\imperas/bin/windows32 -lruntimeloader -o faith.exe ./main.o:main.cpp:(.text.startup+0x552): undefined reference `queue<std::shared_ptr<microblazeinstruction> >::~queue()' ./main.o:main.cpp:(.text.startup+0x83a): undefined reference `queue<std::shared_ptr<microblazeinstruction> >::~queue()' c:/mingw/mingw32/bin/../lib/gcc/i686-w64-mingw32/4.7.0/../../../../i686-w64-mingw32/bin/ld.exe: ./main.o: bad reloc address 0x0 in section `.ctors' collect2.exe: error: ld returned 1 exit status makefile:24: recipe target 'faith.exe' failed make: *** [faith.exe] error 1 

i don't know why happening if specified implementation functions in header file, have destructor?

~queue(); 

is not same as

~queue() {}; 

the second implements ~queue, first declares it.

you declared ~queue, defined nowhere. main destroys queue, implicitly calls ~queue. linker tries find it, finds nowhere, , gives error.