"error LNK2001: unresolved external symbol"problem

This is a discussion on "error LNK2001: unresolved external symbol"problem within the C++ Programming forums, part of the General Programming Boards category; Code: compile is OK,but something wrong with link,I don't know what the matter. Help! The code as follows: //stack.h #include<iostream.h> ...

  1. #1
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    Join Date
    May 2009
    Posts
    9

    Question "error LNK2001: unresolved external symbol"problem

    Code:
    compile is OK,but something wrong with link,I don't know what the matter. Help!
    The code  as  follows:
    
    
    //stack.h
    #include<iostream.h>
    template<class TYPE>
    class stack
    {public:
    stack(int s=10);
    ~stack()
    {delete [] stackptr;
    }
    int push(const TYPE&);
    int pop(TYPE&);
    int isFull() const
    {return top==size-1;
    }
    int isEmpty() const
    {return top==-1;
    }
    private:
           int size;
           int top;
           TYPE* stackptr;
    };
    
    
    //stack.cpp
    #include<iostream.h>
    #include"stack.h"
    template<class TYPE>
    stack<TYPE>::stack(int s)
    {size=s>0&&s<1000?s:10;
      top=-1;
      stackptr=new TYPE[size];
    }
    
    template<class TYPE>
    int stack<TYPE>::push(const TYPE& item)
    {if(!isFull())
    {stackptr[++top]=item;
    return 1;
    }
    return 0;
    }
    
    template<class TYPE>
    int stack<TYPE>::pop(TYPE& popvalue)
    {if(!isEmpty())
    {popvalue=stackptr[top--];
    return 1;
    }
    return 0;
    }
    
    
    //main.cpp
    #include<iostream.h>
    #include"stack.h"
    int main()
    {stack<char> charstack;
    char c='a';
    cout<<"pushing elements onto charstack"<<endl;
    while(charstack.push(c))
    {cout<<c<<" ";
    c+=1;
    }
    cout<<endl<<"stack is full.cannot push"<<c<<endl<<"poping elements from charstack"<<endl;
    while(charstack.pop(c))
    cout<<c<<" ";
    cout<<endl<<"stack is empty.cannot pop"<<endl;
    
    stack<float> floatstack(5);
    float f=1.1f;
    cout<<"pushing elements onto floatstack"<<endl;
    while(floatstack.push(f))
    {cout<<f<<" ";
    f+=1.1f;
    }
    cout<<endl<<"stack is full.cannot push"<<f<<endl<<"poping elements from floatstack"<<endl;
    while(floatstack.pop(f))
    cout<<f<<" ";
    cout<<endl<<"stack is empty.cannot pop"<<endl;
    
    stack<int> intstack;
    int i=1;
    cout<<"pushing elements onto intstack"<<endl;
    while(intstack.push(i))
    {cout<<i<<" ";
    i+=1;
    }
    cout<<endl<<"stack is full.cannot push"<<i<<endl<<"poping elements from intstack"<<endl;
    while(intstack.pop(i))
    cout<<i<<" ";
    cout<<endl<<"stack is empty.cannot pop"<<endl;
    return 0;
    }
    
    
    -------------------Configuration: aaa - Win32 Debug--------------------
    Compiling...
    stack.cpp
    main.cpp
    Linking...
    main.obj : error LNK2001: unresolved external symbol "public: int __thiscall stack<int>::pop(int &)" (?pop@?$stack@H@@QAEHAAH@Z)
    main.obj : error LNK2001: unresolved external symbol "public: int __thiscall stack<int>::push(int const &)" (?push@?$stack@H@@QAEHABH@Z)
    main.obj : error LNK2001: unresolved external symbol "public: __thiscall stack<int>::stack<int>(int)" (??0?$stack@H@@QAE@H@Z)
    main.obj : error LNK2001: unresolved external symbol "public: int __thiscall stack<float>::pop(float &)" (?pop@?$stack@M@@QAEHAAM@Z)
    main.obj : error LNK2001: unresolved external symbol "public: int __thiscall stack<float>::push(float const &)" (?push@?$stack@M@@QAEHABM@Z)
    main.obj : error LNK2001: unresolved external symbol "public: __thiscall stack<float>::stack<float>(int)" (??0?$stack@M@@QAE@H@Z)
    main.obj : error LNK2001: unresolved external symbol "public: int __thiscall stack<char>::pop(char &)" (?pop@?$stack@D@@QAEHAAD@Z)
    main.obj : error LNK2001: unresolved external symbol "public: int __thiscall stack<char>::push(char const &)" (?push@?$stack@D@@QAEHABD@Z)
    main.obj : error LNK2001: unresolved external symbol "public: __thiscall stack<char>::stack<char>(int)" (??0?$stack@D@@QAE@H@Z)
    Debug/aaa.exe : fatal error LNK1120: 9 unresolved externals
    执行 link.exe 时出错.
    
    aaa.exe - 1 error(s), 0 warning(s)

  2. #2
    Registered User
    Join Date
    Jan 2010
    Posts
    3
    Hello,

    That's a common problem . You've created the definition and implementation of the template in separate files, which is something C++ compilers barely tolerate. Put the implementation of the template together with the declaration in the header file; it should compile then.

  3. #3
    and the hat of wrongness Salem's Avatar
    Join Date
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    Location
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    Posts
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    Read this SourceForge.net: Indentation - cpwiki

    Then perhaps more people will read your code.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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