Template function declaration error

Hi all,

I wrote a program to count the number of times an item appears in a list using a sequential search. I had numerous errors and corrected most of them by way of online tutorials, loking up compiler error codes, and textbooks. I still have a few errors that I can't seem to correct, basically something is wrong with the way I'm declaring the functions as templates. Here's the code with the compiler errors.

Code:

---

#include<iostream>
#include<string>
#include<list>

using namespace std;

template <typename T>
int count(const list<string>& aList, const T& item);

template <typename T>
typename list<T>::iterator seqSearch(typename list<T>::const_iterator first, typename list<T>::const_iterator last, const T& target);

int main() {
    string arr[] = { "the", "boy", "the", "girl", "the", "person", "the man" };
    int arrSize = sizeof(arr) / sizeof(*arr);
    list<string> strList(arr, arr + arrSize);
    list<string>::const_iterator iter = strList.begin();

    int wordCount = count(strList, *iter);
    cout << endl << "The number of times 'the' is in the list is: " << wordCount << endl << endl;

    return 0;
}


template <typename T>
int count(const list<string>& aList, const T& item){
        int itemCount = 0;

        //set iterator to the beginning of the list
        list<T>::const_iterator iter = aList.begin();

        //make repeated calls to seqSearch until we reach the end
        while (iter != aList.end()){
                iter = seqSearch(iter, aList.end(), item);
                        if (iter != aList.end()){
                       
                        //seqSearch will only return an iterator when item is found in the list
                        itemCount++;
                        iter++;
                        }

        }
        return itemCount;
}

template <typename T>
typename list<T>::iterator seqSearch(typename list<T>::const_iterator start, typename list<T>::const_iterator last, const T& target){

        //compare list elements with target until either we arrive
        //at last or locate target
        while (start != last && (*start != target))
                start++;

        //iter either points to target or is last
        return start;
}

---

Code:

---

------ Build started: Project: chapt6_quest23b, Configuration: Debug Win32 ------
Compiling...
seqSearch2.cpp
c:\documents and settings\welkj01\my documents\visual studio 2005\projects\chapt6_quest23b\chapt6_quest23b\seqsearch2.cpp(56) : error C2664: 'std::list<_Ty>::_Iterator<_Secure_validation>::_Iterator(std::_List_nod<_Ty,_Alloc>::_Node *,const std::list<_Ty> *)' : cannot convert parameter 1 from 'std::list<_Ty>::_Const_iterator<_Secure_validation>' to 'std::_List_nod<_Ty,_Alloc>::_Node *'
        with
        [
            _Ty=std::string,
            _Secure_validation=true,
            _Alloc=std::allocator<std::string>
        ]
        and
        [
            _Ty=std::string,
            _Secure_validation=true
        ]
        and
        [
            _Ty=std::string,
            _Alloc=std::allocator<std::string>
        ]
        No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
        c:\documents and settings\welkj01\my documents\visual studio 2005\projects\chapt6_quest23b\chapt6_quest23b\seqsearch2.cpp(35) : see reference to function template instantiation 'std::list<_Ty>::_Iterator<_Secure_validation> seqSearch<T>(std::list<_Ty>::_Const_iterator<true>,std::list<_Ty>::_Const_iterator<true>,const T &)' being compiled
        with
        [
            _Ty=std::string,
            _Secure_validation=true,
            T=std::basic_string<char,std::char_traits<char>,std::allocator<char>>
        ]
        c:\documents and settings\welkj01\my documents\visual studio 2005\projects\chapt6_quest23b\chapt6_quest23b\seqsearch2.cpp(19) : see reference to function template instantiation 'int count<std::basic_string<_Elem,_Traits,_Ax>>(const std::list<_Ty> &,const T &)' being compiled
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>,
            _Ax=std::allocator<char>,
            _Ty=std::string,
            T=std::basic_string<char,std::char_traits<char>,std::allocator<char>>
        ]
Build log was saved at "file://c:\Documents and Settings\welkj01\My Documents\Visual Studio 2005\Projects\chapt6_quest23b\chapt6_quest23b\Debug\BuildLog.htm"
chapt6_quest23b - 1 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

---

Thank you in advance for your time and any help you can provide.

Can I ask why you're even bothering, when std::find() does precisely this already?

EDIT: I don't mean my comment to sound nasty. I'm seriously wondering whether this is because you CAN'T use std::find() or you simply aren't aware of it.

Quote:

---

Originally Posted by jaw24

Code:

---

//set iterator to the beginning of the list
        typename list<T>::const_iterator iter = aList.begin();

---

---

I see a missing typename there, that might be it.

Quote:

---

Can I ask why you're even bothering, when std::find() does precisely this already?

EDIT: I don't mean my comment to sound nasty. I'm seriously wondering whether this is because you CAN'T use std::find() or you simply aren't aware of it.

---

I didn't take it as nasty. This was part of project that I just handed in. We had to just write the functions, I wanted to test them in a program before I handed it in, where I found out that it didn't work. This whole template function thing is driving me insane. Everytime I make a correction based on info I find on the web I just get more errors, I'm just chasing my tail.

To AverageSoftware,
The missing typename didn't help, but thank you for your suggestion.

well on line 56, you are returning 'start' which is a list<T>::const_iterator, but the return type of the function is list<T>::iterator. you can't convert from const_iterator to iterator.

change the return type to const_iterator and you're sweet.

Thank you for your replies, here is where it stands now. I am down to one error(at least until I make the next correction).

Code:

---

#include<iostream>
#include<string>
#include<list>

using namespace std;

template <typename T>
int count(const list<string>& aList, const string& item);

template <typename T>
typename list<T>::iterator seqSearch(typename list<T>::const_iterator first, typename list<T>::const_iterator last, const T& target);

int main() {
    string arr[] = { "the", "boy", "the", "girl", "the", "person", "the man" };
    int arrSize = sizeof(arr) / sizeof(*arr);
    const list<string> strList(arr, arr + arrSize);
    list<string>::const_iterator iter = strList.begin();

        const string wordToCount = "the";
    int wordCount = count(strList, wordToCount);
    cout << endl << "The number of times 'the' is in the list is: " << wordCount << endl << endl;

    return 0;
}


template <typename T>
int count(const list<string>& aList, const string& item){
        int itemCount = 0;

        //set iterator to the beginning of the list
        typename list<T>::const_iterator iter = aList.begin();

        //make repeated calls to seqSearch until we reach the end
        while (iter != aList.end()){
                iter = seqSearch(iter, aList.end(), item);
                        if (iter != aList.end()){
                       
                        //seqSearch will only return an iterator when item is found in the list
                        itemCount++;
                        iter++;
                        }

        }
        return itemCount;
}

template <typename T>
typename list<T>::const_iterator seqSearch(typename list<T>::const_iterator start, typename list<T>::const_iterator last, const T& target){

        //compare list elements with target until either we arrive
        //at last or locate target
        while (start != last && (*start != target))
                start++;

        //iter either points to target or is last
        return start;
}

---

and here is the error.

Code:

---

------ Build started: Project: chapt6_quest23b, Configuration: Debug Win32 ------
Compiling...
seqSearch2.cpp
c:\documents and settings\welkj01\my documents\visual studio 2005\projects\chapt6_quest23b\chapt6_quest23b\seqsearch2.cpp(20) : error C2783: 'int count(const std::list<_Ty> &,const std::string &)' : could not deduce template argument for 'T'
        with
        [
            _Ty=std::string
        ]
        c:\documents and settings\welkj01\my documents\visual studio 2005\projects\chapt6_quest23b\chapt6_quest23b\seqsearch2.cpp(8) : see declaration of 'count'
Build log was saved at "file://c:\Documents and Settings\welkj01\My Documents\Visual Studio 2005\Projects\chapt6_quest23b\chapt6_quest23b\Debug\BuildLog.htm"
chapt6_quest23b - 1 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

---

I looked up the error code on msdn2.com and found basically no help. Why is it that you must explicitly declare a variable type in some function templates, which seems to be the issue with my program.

The problem is that the template type T doesn't appear in the argument list of count. Therefore, the compiler cannot figure out what it is.

In that case, you need to call count like so:

Code:

---

count<int>(/*args*/);

---

This is assuming you want int to replace T, of course.

Addendum:
Looking more closely at the code, did you actually want this:

Code:

---

template <typename T>
int count(const list<T>& aList, const string& item)

---

Quote:

---

In that case, you need to call count like so:

Code:
count<int>(/*args*/);

---

Quote:

---

Looking more closely at the code, did you actually want this:

Code:
template <typename T>
int count(const list<T>& aList, const string& item)

---

I had tried both of those prior to posting to the board, they created more errors. I tried using count as a non-templated function, still more errors. Where I have it now is the least amount of errors I have had.

Quote:

---

Originally Posted by jaw24

I had tried both of those prior to posting to the board, they created more errors. I tried using count as a non-templated function, still more errors. Where I have it now is the least amount of errors I have had.

---

Ah, I see now. I just finally took the time to understand what you're doing.

You want this:

Code:

---

template <typename T>
int count(const list<T>& aList, const T& item)

---

Like you had originally.

Gosh, aren't templates fun?

Addendum:
You also need to update the prototype for seqSearch to return a const_iterator, it doesn't match the actual function.

With these changes, the code compiles and runs on my system.

Thank you, thank you, thank you!!! Works for me now also. I really appreciate your help.

edit: Yes, templates are a blast, I think they become more of a hoot when you throw in iterators.