Thread: Database Class.

This is a very very simple database software I am creating.

Code:

#include <string>
#include <list>





class BUBBELdb {


public:
	std::string query; // our query string
	

	int ParseQuery( std::string query )
	{

		(*this).query = query;

		std:: list< std::string > keywords;

		/**

		I was going to make a totally different header file for these keywords ( using #define ), but what the heck.
		
		
		*/

		// --- List keyword types
		keywords.push_back("GET");   // To grab columns from tables
		keywords.push_back("FROM");  // To grab tables
		keywords.push_back("JOIN");  // To Join other tables
		keywords.push_back("WHERE"); // To find if a certain column contains a certain value
		keywords.push_back("SET");	 // To set columns to certain values
		keywords.push_back("UNION"); // To cluster our GET clauses
		// --- end List keyword types
	

		for ( int i = keywords.front(); i<keywords.back();/* .end() doesn't work either. */ i++ )
		{

			if ( keywords[i].find(keywords[i].c_str(), NULL ) )
			{

				return 1;

			}

		}


		return 0;
	}

Errors:

Code:

1>------ Build started: Project: database, Configuration: Debug Win32 ------
1>Compiling...
1>main.cpp
1>main.h(41) : error C2440: 'initializing' : cannot convert from 'std::basic_string<_Elem,_Traits,_Ax>' to 'int'
1>        with
1>        [
1>            _Elem=char,
1>            _Traits=std::char_traits<char>,
1>            _Ax=std::allocator<char>
1>        ]
1>        No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
1>main.h(41) : error C2784: 'bool std::operator <(const std::list<_Ty,_Ax> &,const std::list<_Ty,_Ax> &)' : could not deduce template argument for 'const std::list<_Ty,_Ax> &' from 'int'
1>        c:\program files\microsoft visual studio 9.0\vc\include\list(1310) : see declaration of 'std::operator <'
1>main.h(41) : error C2784: 'bool std::operator <(const std::basic_string<_Elem,_Traits,_Alloc> &,const _Elem *)' : could not deduce template argument for 'const std::basic_string<_Elem,_Traits,_Alloc> &' from 'int'
1>        c:\program files\microsoft visual studio 9.0\vc\include\string(150) : see declaration of 'std::operator <'
1>main.h(41) : error C2784: 'bool std::operator <(const _Elem *,const std::basic_string<_Elem,_Traits,_Alloc> &)' : could not deduce template argument for 'const _Elem *' from 'int'
1>        c:\program files\microsoft visual studio 9.0\vc\include\string(140) : see declaration of 'std::operator <'
1>main.h(41) : error C2784: 'bool std::operator <(const std::basic_string<_Elem,_Traits,_Alloc> &,const std::basic_string<_Elem,_Traits,_Alloc> &)' : could not deduce template argument for 'const std::basic_string<_Elem,_Traits,_Alloc> &' from 'int'
1>        c:\program files\microsoft visual studio 9.0\vc\include\string(130) : see declaration of 'std::operator <'
1>main.h(41) : error C2784: 'bool std::operator <(const std::reverse_iterator<_RanIt> &,const std::reverse_iterator<_RanIt2> &)' : could not deduce template argument for 'const std::reverse_iterator<_RanIt> &' from 'int'
1>        c:\program files\microsoft visual studio 9.0\vc\include\xutility(2236) : see declaration of 'std::operator <'
1>main.h(41) : error C2784: 'bool std::operator <(const std::_Revranit<_RanIt,_Base> &,const std::_Revranit<_RanIt2,_Base2> &)' : could not deduce template argument for 'const std::_Revranit<_RanIt,_Base> &' from 'int'
1>        c:\program files\microsoft visual studio 9.0\vc\include\xutility(2046) : see declaration of 'std::operator <'
1>main.h(41) : error C2784: 'bool std::operator <(const std::pair<_Ty1,_Ty2> &,const std::pair<_Ty1,_Ty2> &)' : could not deduce template argument for 'const std::pair<_Ty1,_Ty2> &' from 'int'
1>        c:\program files\microsoft visual studio 9.0\vc\include\utility(84) : see declaration of 'std::operator <'
1>main.h(41) : error C2677: binary '<' : no global operator found which takes type 'std::basic_string<_Elem,_Traits,_Ax>' (or there is no acceptable conversion)
1>        with
1>        [
1>            _Elem=char,
1>            _Traits=std::char_traits<char>,
1>            _Ax=std::allocator<char>
1>        ]
1>main.h(44) : error C2676: binary '[' : 'std::list<_Ty>' does not define this operator or a conversion to a type acceptable to the predefined operator
1>        with
1>        [
1>            _Ty=std::string
1>        ]
1>main.h(44) : error C2228: left of '.find' must have class/struct/union
1>main.h(44) : error C2676: binary '[' : 'std::list<_Ty>' does not define this operator or a conversion to a type acceptable to the predefined operator
1>        with
1>        [
1>            _Ty=std::string
1>        ]
1>main.h(44) : error C2228: left of '.c_str' must have class/struct/union
1>Build log was saved at "file://Debug\BuildLog.htm"
1>database - 13 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Most of this seems to be complaining about operators, so should I operator overload it?

Originally Posted by laserlight

What does the BUBBELdb class model?

At the moment, the main problem seems to be that you are not reading documentation correctly. You should have understood that front() returns a reference to the front of the container. For a std:: list< std::string >, this is a reference to a std::string, which certainly is not an int. You probably wanted to use begin(), but begin() for a std::list<std::string> returns a std::list<std::string>::iterator, not an int.

I KEEP PRESSING BACK AND THE MESSAGE IS BEING CLEARED D:

Look, I tried begin aswell it gave me errors, and I haven't done iterators yet.

By the way, I used size too. ;P

I also tried vectors.

Originally Posted by laserlight

Keep a text editor open for composing your posts.


The body of your loop is wrong as well, but I cannot figure out what you had in mind when you wrote it. Doubly linked lists do not allow for random access, or even faster than linear time access, so operator[] is not overloaded for std::list. Consequently, it makes sense to use iterators here, e.g.,

Code:

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

int main()
{
    std::list<std::string> keywords;
    keywords.push_back("GET");   // To grab columns from tables
    keywords.push_back("FROM");  // To grab tables
    keywords.push_back("JOIN");  // To Join other tables
    keywords.push_back("WHERE"); // To find if a certain column contains a certain value
    keywords.push_back("SET");	 // To set columns to certain values
    keywords.push_back("UNION"); // To cluster our GET clauses

    for (std::list<std::string>::iterator i = keywords.begin(), end = keywords.end();
        i != end; ++i)
    {
        std::cout << *i << std::endl;
    }
}

You need to start reading and thinking instead of just doing guess and check.

Do I have to do it in an int main?

Well .size() does return how many elements are in a list/vector so whats your point in guessing? :P


By the way, I'll just look into the documentation some more, and read up on iterators so.

Originally Posted by rags_to_riches

And Laserlight cranks that one deep and out of the park!!!

With the addition of "and running to the forums as soon as it doesn't work."

Well it's not like I know immediately what the errors are. :P

Originally Posted by laserlight

Why do you think that this is restricted for use in the global main function?


You are guessing how the list traversal is done. This is clear from the fact that you tried begin() and front(), end() and size(), without giving consideration into the type of i. If you carefully consulted a reference, even an online reference like cppreference.comp, you would have had a much better idea of what to do.

The error was not very cryptic. It says that the compiler "cannot convert from 'std::basic_string<_Elem,_Traits,_Ax>' to 'int'". This points to a mistake related to the type of i.

Actually I did read up on begin, front, end, size, but it's not like I read the whole thing. :P

Well thank you for telling me what the error is, but it was cryptic for a nooby xD.

Originally Posted by Elysia

Notes:
1) It's bad practice to define a member in a class and the EXACT same name for something that you take by argument in a function. Separate them somehow - preferably be prefixing members with m_.
2) (*this). is the same as this->.
3) You don't need to use this-> to access members of the class. At least if you follow note 1.
4) You can use Firefox & Session Manager. It keeps saving form data, so if you accidentally hit back or the browser crashes, (most) of it will still be there! Hit the forward button!

I know number 2, and number 4 doesn't work, I do forward it back, but it's still clear.