Custom CVar system

This is a discussion on Custom CVar system within the C++ Programming forums, part of the General Programming Boards category; I am trying to write my own cvar system, similar to that found in quake games. This is my prototype... ...

  1. #1
    using namespace Trooper; St0rmTroop3er's Avatar
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    Custom CVar system

    I am trying to write my own cvar system, similar to that found in quake games.

    This is my prototype...
    Code:
    class rCVarEngine
    {
    	public:
    		void setCVar(const char *name, const char *value);
    		void setNewCVar(const char *name, const char *value);
    		const char returnCVar(const char *name);
    	private:
    		rCVar *cvarList;
    };
    and I get this error for it...
    rCVar.h:31: error: multiple types in one declaration
    Then in this function where I return cvarList->value...
    Code:
    const char rCVarEngine::returnCVar(const char *name)
    {
    	while(cvarList)
    	{
    		if(cvarList->name == name)
    		{
    			return cvarList->value;			
    		} else {
    			cvarList = cvarList->next;
    		}
    		
    	}
    }
    I get this error:

    rCVar.h:74: error: invalud conversion from 'const char*' to 'char'
    Any help on fixing this would be great! I am using GCC v 3.4.2

  2. #2
    Frequently Quite Prolix dwks's Avatar
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    Code:
    const char rCVarEngine::returnCVar(const char *name)
    Perhaps this function is suposed to return a const char*?
    Code:
    const char *rCVarEngine::returnCVar(const char *name)
    dwk

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  3. #3
    Registered User Tonto's Avatar
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    Code:
    if(cvarList->name == name)
    C strings can be compared with strcmp(..)

  4. #4
    using namespace Trooper; St0rmTroop3er's Avatar
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    Thanks! I still get the multiple types in one declaration error, in the class declaration.

  5. #5
    Registered User Tonto's Avatar
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    I get the multiple type declaration errors when I forget to put a semi-colon after the class. Could this be the case, or could you show us where the exact line is?

  6. #6
    using namespace Trooper; St0rmTroop3er's Avatar
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    Code:
    class rCVarEngine
    {
    	public:
    		void setCVar(const char *name, const char *value);
    		void setNewCVar(const char *name, const char *value);
    		const char* returnCVar(const char *name);
    	private:
    		rCVar *cvarList;
    }; //<-- Error here, line 31

  7. #7
    Registered User Tonto's Avatar
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    And what is before that? I highly suspect that it's simply a missing semi-colon.

  8. #8
    using namespace Trooper; St0rmTroop3er's Avatar
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    Well, you were right. I forgot a ; in my struct above my class :P

    *sighs
    Now I get these errors that I have no idea what they mean.
    C:/DOCUME~1/ryan/LOCALS~1/Temp/ccUDbaaa.o(.text+0xd):test.cpp: undefined reference to `std::string::size() const'
    C:/DOCUME~1/ryan/LOCALS~1/Temp/ccUDbaaa.o(.text+0x60):test.cpp: undefined reference to `std::string:perator[](unsigned int) const'
    C:/DOCUME~1/ryan/LOCALS~1/Temp/ccUDbaaa.o(.text+0x9f):test.cpp: undefined reference to `std::string:perator[](unsigned int) const'
    C:/DOCUME~1/ryan/LOCALS~1/Temp/ccUDbaaa.o(.text+0xce):test.cpp: undefined reference to `std::string:perator[](unsigned int) const'
    C:/DOCUME~1/ryan/LOCALS~1/Temp/ccUDbaaa.o(.text+0x23b):test.cpp: undefined reference to `std::cout'
    C:/DOCUME~1/ryan/LOCALS~1/Temp/ccUDbaaa.o(.text+0x240):test.cpp: undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std:perator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)'
    C:/DOCUME~1/ryan/LOCALS~1/Temp/ccUDbaaa.o(.text+0x275):test.cpp: undefined reference to `std::ios_base::Init::Init()'
    C:/DOCUME~1/ryan/LOCALS~1/Temp/ccUDbaaa.o(.text+0x290):test.cpp: undefined reference to `std::ios_base::Init::~Init()'
    collect2: ld returned 1 exit status

  9. #9
    using namespace Trooper; St0rmTroop3er's Avatar
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    Ok, it compiles fine, but now the program crashes when I run this function:

    Code:
    void rCVarEngine::setNewCVar(const char *name, const char *value)
    {
    	cvarList->next = 0;
    	
    	if(cvarList == 0)
    	{
    		strcpy((char*)cvarList->name, name);
    		strcpy((char*)cvarList->value, value);
    		return;
    	}
    	
    	rCVar *current = cvarList;
    	while(current->next)
    	{
    		current = current->next;
    	}
    	
    	current->next = cvarList;
    	cvarList->next = (rCVar*)0;
    }

  10. #10
    Registered User Tonto's Avatar
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    Code:
    	if(cvarList == 0)
    	{
    		strcpy((char*)cvarList->name, name);
    		strcpy((char*)cvarList->value, value);
    		return;
    	}
    Operating on a null pointer

  11. #11
    using namespace Trooper; St0rmTroop3er's Avatar
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    Well, what that is doing, is if there is nothing set on cvarList, then set thoe values, instead of moving to the next object.

  12. #12
    Just Lurking Dave_Sinkula's Avatar
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    Quote Originally Posted by St0rmTroop3er
    Well, what that is doing, is if there is nothing set on cvarList, then set thoe values, instead of moving to the next object.
    No. Look at it.
    Quote Originally Posted by Tonto
    Code:
    	if(cvarList == 0)
    	{
    		strcpy((char*)cvarList->name, name);
    		strcpy((char*)cvarList->value, value);
    		return;
    	}
    Operating on a null pointer
    If cvarList is a NULL pointer, then dereference it.


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  13. #13
    using namespace Trooper; St0rmTroop3er's Avatar
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    Ah, ok I fixed it... but it still crashes. I revamped it so I don't have two functions, one to set a new one and one to set an exisiting one. Hopefully I didn't mess it up.

    Linked Lists are big ol pain in the butt...and its so hard to understand them.

    Code:
    void rCVarEngine::set(const char *name, const char *value,bool lock)
    {
    	// If our head pointer is blank, then fill that first.
    	if(head == 0)
    	{
    		head->name = name;
    		head->value = value;
    		head->locked = lock;
    		return;
    	}
    	
    	while(cvarList)
    	{
    		// If we found an existing CVar
    		// then set its value and lock
    		// mode
    		if(cvarList->name == name)
    		{
    			cvarList->value = value;
    			cvarList->locked = lock;
    			return;
    		//Else if the next in the list is empty
    		// Set its new values
    		} else if(cvarList->next == 0) {
    	
    			// Create a temporary cvar
    			rCVar *newVar = new rCVar;
    			// Set its value
    			newVar->name = name;
    			newVar->value = value;
    			newVar->locked = lock;
    			newVar->next = 0;
    			
    			rCVar *temp = head;
    			while(temp->next)
    			{
    				temp = temp->next;
    			}
    			
    			// Add it to the end
    			temp->next = newVar;
    		// If we havn't found the end of the
    		// list or if we havn't found a pre-
    		// existing cvar, then move to the 
    		// next in the list
    		} else {
    			cvarList = cvarList->next;
    		} 
    		
    	}
    	
    }
    NOTE* I am following examples in C++ for Dummies 4th Edition.

  14. #14
    Registered User Tonto's Avatar
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    Code:
    	if(head == 0)
    	{
    		head->name = name;
    		head->value = value;
    		head->locked = lock;
    		return;
    	}
    You're trying to dereference a null pointer again, allocate memory for it first, then set values. You might find it useful to have two auxillary pointers, head and tail, pointing to the first and last members of the list respectively.

    Code:
    if(cvarList->name == name)
    Probably need strcmp, unless they are std::string's now.

  15. #15
    using namespace Trooper; St0rmTroop3er's Avatar
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    Ok I added strcmp.

    I don't know how to allocate memory for that. :P Would it be better if I did

    if(strcmp(head->name,""))

    To check if it is empty?
    Your mom is like a struct, she has no class

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