pointers and vectors

This is a discussion on pointers and vectors within the C++ Programming forums, part of the General Programming Boards category; I have a program that takes customer information ( such as name, address, city and state ect....) from a disk ...

  1. #1
    Master of Puppets rwmarsh's Avatar
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    Question pointers and vectors

    I have a program that takes customer information ( such as name, address, city and state ect....) from a disk file and loads it into a vector. Each element of the vector is a struct like this.
    Code:
    struct mystruct
    {
        string name;
        string address;
        string city;
        string state;
        string zip;
        string phone;
    };
    mystruct customers;
    The elements that are saved on disk are in no particular order but I want to be able to sort the vector in alphabetical order to display to the screen. I was thinking about creating a header file with a class called sort to do the dirty work. Can I pass a pointer to the entire vector to this sort class and return a pointer to the new sorted vector back to the program? If so, is the pointer syntax the same and how do I dereference it to replace the old vector with the new sorted vector?
    I know there are functions such as sort that can do this for me but I want to a sort by city, then sort those by name. Plus, I just want to see if I can do it
    Last edited by rwmarsh; 04-01-2006 at 10:25 AM.
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  2. #2
    Master of Puppets rwmarsh's Avatar
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    Here is a simple program I made up real quick. This is as far as I have got.
    Code:
    #include <iostream>
    #include <vector>
    
    using namespace std;
    
    struct mytype
    {
        int one;
        int two;
        int three;
    };
    
    void SortMyVec(vector<mytype>::iterator iter1, vector<mytype>::iterator iter2);
    
    int main()
    {
        mytype numbers;
        
        vector<mytype> myvec;
        vector<mytype>::iterator iter1;
        vector<mytype>::iterator iter2;
    
        numbers.one=5; numbers.two=6; numbers.three=7;
          myvec.push_back(numbers);
        numbers.one=9; numbers.two=0; numbers.three=1;    
          myvec.push_back(numbers);
        numbers.one=1; numbers.two=2; numbers.three=3;
          myvec.push_back(numbers);
        numbers.one=5; numbers.two=3; numbers.three=4;
          myvec.push_back(numbers);
        numbers.one=8; numbers.two=9; numbers.three=0;
          myvec.push_back(numbers);
        
        for (int a=0; a<myvec.size(); a++)
        {
            numbers=myvec.at(a);
            cout<<numbers.one<<" "<<numbers.two<<" "<<numbers.three<<endl;
        }
        cout<<endl;
        
        iter1=myvec.begin();
        iter2=myvec.end();
    
        SortMyVec(iter1, iter2);
    
        for (int a=0; a<myvec.size(); a++)
        {
            numbers=myvec.at(a);
            cout<<numbers.one<<" "<<numbers.two<<" "<<numbers.three<<endl;
        }
        cout<<endl;
    
        cin.get();
        return 0;
    }
    
    void SortMyVec(vector<int>::iterator iter1, vector<int>::iterator iter2)
    {
        sort(iter1, iter2);
    
        return;
    }
    What I want to do is sort the vector by the first integer and then by the second integer so my output is like this
    Code:
    1 2 3
    5 3 4 
    5 6 7
    8 9 0 
    9 0 1
    It works fine if I use just a single integer for each element of the vector instead of the struct. But when I use the struct I get
    Code:
      [Linker error] undefined reference to `SortMyVec(__gnu_cxx::__normal_iterator<mytype*, std::vector<mytype, std::allocator<mytype> > >, __gnu_cxx::__normal_iterator<mytype*, std::vector<mytype, std::allocator<mytype> > >)'
    I am not sure where to go from here. Anyone got ay ideas?
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  3. #3
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    All you need is to create a sorting function for your struct:
    Code:
    bool mystructLess(const mystruct& lhs, const mystruct& rhs)
    {
      // return true if lhs < rhs, return false if lhs >= rhs.
    }
    Then just pass this to the sort function:
    Code:
    std::sort(myvec.begin(), myvec.end(), myStructLess);
    The only hard part is filling in the code for the mystructLess function. If you only want to sort by name it would be easy, but it gets more complicated if you want to sort by multiple members of the struct.

  4. #4
    C++ Witch laserlight's Avatar
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    I want to a sort by city, then sort those by name
    Define say:
    Code:
    bool cmp_mystruct(const mystruct& a, const mystruct& b) {
    	if (a.city == b.city) {
    		return a.name < b.name;
    	} else {
    		return a.city < b.city;
    	}
    }
    Then use std::sort()
    Code:
    std::sort(myvec.begin(), myvec.end(), cmp_mystruct);
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  5. #5
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    1) The parameter types in your function declaration before main() do not match the parameter types in the function definition after main().

    2) Instead of this type of loop:
    Code:
    for (int a=0; a<myvec.size(); a++)
    {
            numbers=myvec.at(a);
            cout<<numbers.one<<" "<<numbers.two<<" "<<numbers.three<<endl;
    }
    use iterators:
    Code:
    for(iter = myvec.begin(); iter != myvec.end(); ++iter)
    {
    
    
    }

  6. #6
    Master of Puppets rwmarsh's Avatar
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    OK, That works great! But something still seems strange to me. Here's what I got
    Code:
    #include <iostream>
    #include <vector>
    
    using namespace std;
    
    struct mytype
    {
        int one;
        int two;
        int three;
    };
    
    bool SortMyStruct(const mytype& a, const mytype& b);
    
    int main()
    {
        mytype numbers;
        
        vector<mytype> myvec;
        vector<mytype>::iterator iter;
    
        numbers.one=5; numbers.two=6; numbers.three=7;
          myvec.push_back(numbers);
        numbers.one=9; numbers.two=0; numbers.three=1;    
          myvec.push_back(numbers);
        numbers.one=1; numbers.two=2; numbers.three=3;
          myvec.push_back(numbers);
        numbers.one=5; numbers.two=3; numbers.three=4;
          myvec.push_back(numbers);
        numbers.one=8; numbers.two=9; numbers.three=0;
          myvec.push_back(numbers);
        numbers.one=5; numbers.two=3; numbers.three=5;
          myvec.push_back(numbers);
        
        for (iter=myvec.begin(); iter!=myvec.end(); ++iter)
        {
            numbers=*iter;
            cout<<numbers.one<<" "<<numbers.two<<" "<<numbers.three<<endl;
        }
        cout<<endl;
        
        sort(myvec.begin(), myvec.end(), SortMyStruct);
    
        for (iter=myvec.begin(); iter!=myvec.end(); ++iter)
        {
            numbers=*iter;
            cout<<numbers.one<<" "<<numbers.two<<" "<<numbers.three<<endl;
        }
        cout<<endl;
    
        cin.get();
        return 0;
    }
    
    bool SortMyStruct(const mytype& a, const mytype& b) 
    {
        if (a.one == b.one) 
        {
            if (a.two == b.two)
                return a.three < b.three;
            else
                return a.two < b.two;   
        }
        else 
            return a.one < b.one;
    }
    Is there any way I can tighten this up any?
    Maybe it is all the different return statements in the SortMyStruct function, I'm used to having only one return in any given function.I realize they have to be there, it just does not seem right.

    BTW, Thanks again for the help!
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  7. #7
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    Compare this:
    Code:
    for (iter=myvec.begin(); iter!=myvec.end(); ++iter)
    {
    	numbers=*iter;
    	cout<<numbers.one<<" "<<numbers.two<<" "<<numbers.three<<endl;
    }
    to this:
    Code:
    for (iter=myvec.begin(); iter!=myvec.end(); ++iter)
    {
    	cout<<iter->one<<" "<<iter->two<<" "<<iter->three<<endl;
    }
    Maybe it is all the different return statements in the SortMyStruct function, I'm used to having only one return in any given function.I realize they have to be there, it just does not seem right.
    You don't have to have more than one return statement:
    Code:
    bool SortMyStruct(const mytype& a, const mytype& b) 
    {
        bool result;
    
        if (a.one == b.one) 
        {
            if (a.two == b.two)
               result =  a.three < b.three;
            else
                result = a.two < b.two;   
        }
        else 
        {
            result =  a.one < b.one;
        }
    	
        return result;
    }

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