Programming Forums > Application Development > C++

Jessehk · Jun 26th, 2006, 7:31 PM

I'm attempting to use std::find() to located a specific element in a std::vector, and for some reason, When I try to create a std::vector<T>::iterator, g++ complains.

Does anyone know my problem?

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#include <vector>
#include <iostream>
#include <cstddef>
#include <stdexcept>
#include <string>
#include <iterator>
#include <algorithm>

template<typename T, size_t capacity=5>
class Basket {
    private:
        const size_t m_capacity;
        std::vector<T> m_items;
    public:
        class CapacityError : public std::length_error {
            public:
                CapacityError(const std::string &msg)
                    : length_error(msg) {
                }
        };

        class ItemNotFoundError : public std::invalid_argument {
            public:
                ItemNotFoundError(const std::string &msg)
                    : invalid_argument(msg) {
                }
        };
        
        Basket()
            : m_capacity(capacity),
              m_items(0) {
        }

        void add_item(const T &item) {
            if(m_items.size() + 1 > m_capacity)
                throw CapacityError("The Basket it full!");
            else
                m_items.push_back(item);
        }

        void remove_item(const T &item) {
            std::vector<T>::iterator pos;
            pos = find(m_items.begin(), m_items.end(), item);

            if(pos != m_items.end())
                m_items.erase(pos);
            else
                throw ItemNotFoundError("The specified item was not found in the Basket.");
        }
};

int main() {
    Basket<int> basket;

    return 0;
}

ERRORS

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basket.cpp: In member function ‘void Basket<T, capacity>::remove_item(const T&)’:
basket.cpp:42: error: expected `;' before ‘pos’
basket.cpp:43: error: ‘pos’ was not declared in this scope

Cache · Jun 26th, 2006, 10:34 PM

Compiles fine in VC++ 2005, but not Dev-C++ (with g++.exe). It works OK if you typename it thought.

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typename std::vector<T>::iterator iter = 
  std::find(m_items.begin(), m_items.end(), item);

Narue · Jun 27th, 2006, 8:44 AM

>std::vector<T>::iterator pos;
vector<T>::iterator is a type that depends on a template argument (T being that argument). In such a case you have to specify that you're referring to a type rather than a "thing" by using the typename keyword:

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typename std::vector<T>::iterator pos;

Jessehk · Jun 27th, 2006, 9:23 AM

Thanks Narue and Cache.

There is so much more to C++ then I once thought. I know the basics, but some template and class features are incredibly complicated :eek:.

Narue · Jun 27th, 2006, 9:42 AM

>some template and class features are incredibly complicated
I think that templates are the most complicated feature of C++. It's basically a turing complete sub-language. There's a lot of power, but only if you can wrap your brain around it.

Game_Ender · Jun 28th, 2006, 8:36 AM

Quote:

Originally Posted by Cache

Compiles fine in VC++ 2005, but not Dev-C++ (with g++.exe). It works OK if you typename it thought.

On a side not, is it standards compliant to compile without the typename? I have done some pretty heavy template stuff with GCC 4.0.x and it always requires typename, the error messages even tell you to use it. I was quite supprised to see a helpful error message from the compilier.

Narue · Jun 28th, 2006, 9:17 AM

>On a side not, is it standards compliant to compile without the typename?
No, in strict mode, a compliant compiler should produce a diagnostic message.

grumpy · Jun 28th, 2006, 9:26 AM

Quote:

Originally Posted by Narue

No, in strict mode, a compliant compiler should produce a diagnostic message.

You're right but, at the risk of being picky .... I would probably make the statement outside in, whereas you have made it inside out.

A compliant compiler should produce a diagnostic. A compiler that is non-compliant may not. Some compilers, by default, are a bit relaxed about standard compliance (i.e. the "strict mode", as you describe it, is disabled by default).

Jun 26th, 2006, 7:31 PM	#1
Jessehk The Oblivious One Join Date: May 2005 Location: Ontario, Canada Posts: 644 Rep Power: 4	std::vector<T>::iterator not recognised? I'm attempting to use std::find() to located a specific element in a std::vector, and for some reason, When I try to create a std::vector<T>::iterator, g++ complains. Does anyone know my problem? (Toggle Plain Text) #include <vector> #include <iostream> #include <cstddef> #include <stdexcept> #include <string> #include <iterator> #include <algorithm> template<typename T, size_t capacity=5> class Basket { private: const size_t m_capacity; std::vector<T> m_items; public: class CapacityError : public std::length_error { public: CapacityError(const std::string &msg) : length_error(msg) { } }; class ItemNotFoundError : public std::invalid_argument { public: ItemNotFoundError(const std::string &msg) : invalid_argument(msg) { } }; Basket() : m_capacity(capacity), m_items(0) { } void add_item(const T &item) { if(m_items.size() + 1 > m_capacity) throw CapacityError("The Basket it full!"); else m_items.push_back(item); } void remove_item(const T &item) { std::vector<T>::iterator pos; pos = find(m_items.begin(), m_items.end(), item); if(pos != m_items.end()) m_items.erase(pos); else throw ItemNotFoundError("The specified item was not found in the Basket."); } }; int main() { Basket<int> basket; return 0; } #include <vector> #include <iostream> #include <cstddef> #include <stdexcept> #include <string> #include <iterator> #include <algorithm> template<typename T, size_t capacity=5> class Basket { private: const size_t m_capacity; std::vector<T> m_items; public: class CapacityError : public std::length_error { public: CapacityError(const std::string &msg) : length_error(msg) { } }; class ItemNotFoundError : public std::invalid_argument { public: ItemNotFoundError(const std::string &msg) : invalid_argument(msg) { } }; Basket() : m_capacity(capacity), m_items(0) { } void add_item(const T &item) { if(m_items.size() + 1 > m_capacity) throw CapacityError("The Basket it full!"); else m_items.push_back(item); } void remove_item(const T &item) { std::vector<T>::iterator pos; pos = find(m_items.begin(), m_items.end(), item); if(pos != m_items.end()) m_items.erase(pos); else throw ItemNotFoundError("The specified item was not found in the Basket."); } }; int main() { Basket<int> basket; return 0; } ERRORS (Toggle Plain Text) basket.cpp: In member function ‘void Basket<T, capacity>::remove_item(const T&)’: basket.cpp:42: error: expected `;' before ‘pos’ basket.cpp:43: error: ‘pos’ was not declared in this scope basket.cpp: In member function ‘void Basket<T, capacity>::remove_item(const T&)’: basket.cpp:42: error: expected `;' before ‘pos’ basket.cpp:43: error: ‘pos’ was not declared in this scope __________________ Dr. Zoidberg: [ecstatic] I'm going to a movie... with FRIENDS!

Jun 26th, 2006, 10:34 PM	#2
Cache Hobbyist Join Date: Sep 2005 Posts: 261 Rep Power: 4	Compiles fine in VC++ 2005, but not Dev-C++ (with g++.exe). It works OK if you typename it thought. (Toggle Plain Text) typename std::vector<T>::iterator iter = std::find(m_items.begin(), m_items.end(), item); typename std::vector<T>::iterator iter = std::find(m_items.begin(), m_items.end(), item);

Jun 27th, 2006, 8:44 AM	#3
Narue Professional Programmer Join Date: Sep 2005 Posts: 419 Rep Power: 4	>std::vector<T>::iterator pos; vector<T>::iterator is a type that depends on a template argument (T being that argument). In such a case you have to specify that you're referring to a type rather than a "thing" by using the typename keyword: (Toggle Plain Text) typename std::vector<T>::iterator pos; typename std::vector<T>::iterator pos; __________________ Even if the voices aren't real, they have some pretty good ideas.

Jun 27th, 2006, 9:23 AM	#4
Jessehk The Oblivious One Join Date: May 2005 Location: Ontario, Canada Posts: 644 Rep Power: 4	Thanks Narue and Cache. There is so much more to C++ then I once thought. I know the basics, but some template and class features are incredibly complicated :eek:. __________________ Dr. Zoidberg: [ecstatic] I'm going to a movie... with FRIENDS!

Jun 27th, 2006, 9:42 AM	#5
Narue Professional Programmer Join Date: Sep 2005 Posts: 419 Rep Power: 4	>some template and class features are incredibly complicated I think that templates are the most complicated feature of C++. It's basically a turing complete sub-language. There's a lot of power, but only if you can wrap your brain around it. __________________ Even if the voices aren't real, they have some pretty good ideas.

Jun 28th, 2006, 9:17 AM	#7
Narue Professional Programmer Join Date: Sep 2005 Posts: 419 Rep Power: 4	>On a side not, is it standards compliant to compile without the typename? No, in strict mode, a compliant compiler should produce a diagnostic message. __________________ Even if the voices aren't real, they have some pretty good ideas.

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Programming Forums > Application Development > C++

std::vector<T>::iterator not recognised?