Linked List Help

[-Prime-]

I have read the tutorials on this site and have received a decent understanding of how the linked list works, but when I try to actually implement code - well... I kind of get lost. Mainly because what I need to do with my linked list it does not really have an example on how to implement it.

I am in school and for my datastructures class we are constructing a simple DBMS system. I have come to the part of my program where I need to implement a linked list so whenever the user types in "list" it shows a list of all the commands the user has typed in; if they type in "list first" it shows the first command they ever entered, and if they type in "list last" it shows the last command they ever entered.

I mostly just need a few pointers (no pun intended) on how to actually implement a linked list itself for my purposes. I read the tutorials and practiced, which made it seem simple enough, but when I open up my code and try to implement it my mind gets all muddied, so to speak. Mainly I do not understand how I store my commands into the buffer char command[64] I have made.

#include <iostream>
#include <string>
using namespace std;

char inputLine[64];
int index = 0;
char buffer[64];
char bufferIndex = 0;
char* token;


char* getToken() ;
void parseFieldName();
int isValidFieldName();
void parseTableName();
int isValidTableName();
void parseFrom();

// Linked List Variables
struct node {
    char command[64];
    node *next;
    node *prev;
};

struct node *head = NULL;
struct node *tail = NULL;

void addNode(char* cmd) {
    
    node *n1 = (node*)malloc(sizeof(node));	// allocate memory for node
	
}

int isWhiteSpace(char w) {
    if(w == ' ' || w == '\t' || w == '\r')
        return 1;
    else
        return 0;
}

void parseSelect() {
    if(strcmp(token,"select")==0) {
        cout << "SELECT command parsed" << endl;
        parseFieldName();
    } else {
        if(strcmp(token,"from")==0) {
            cout << "Illegal FROM - Missing SELECT" << endl;
        } else {
            cout << "Missing SELECT command" << endl;
        }
    }
}

void parseFieldName() {
    token=getToken();
    
    if(isValidFieldName()) {
        if(strcmp(token,"*")==0) {
            cout << "* command parsed" << endl;
            token = getToken();
            parseFrom();
        } else {
            if(strcmp(token,"from")!=0) {
                //token assumed field name
                token=getToken();
                //token is either FROM or , or error
                while(strcmp(token,"from")!=0) {
                    if(strcmp(token,",")==0) {
                        token = getToken();
                        if(isValidFieldName()) {
                            token = getToken();
                        }
						else {
							cout << "Missing field name" << endl;
							return;
						}
                    }
                    else {
                        cout << "Missing , or FROM" << endl;
                        return;
                    }
                }
            }

            cout << "Field Name(s) Parsed" << endl;
            parseFrom();
        }
    }
}

void parseTableName() {
    token=getToken();
    
    if(strcmp(token,"")==0) {
        cout << "Missing table name" << endl;
    } else {
        if(isValidTableName()){
            cout << "Table Name Parsed" << endl;
        }
    }
}

void parseFrom() {
    if(strcmp(token,"from")==0) {
        cout << "FROM command parsed" << endl;
        parseTableName();
    } else {
        if(strcmp(token,"select")==0) {
            cout << "Illegal SELECT - Missing FROM" << endl;
        } else {
            cout << "Missing FROM command" << endl;
        }
    }
}

int isValidFieldName(){
    if(strcmp(token,"select")==0){
        cout << "Illegal SELECT - Invalid field name" << endl;
        return 0;
    }
        
	if(strcmp(token,"from")==0){
		cout << "Illegal FROM - Invalid field name" << endl;
        return 0;
	}
	
	return 1;
}

int isValidTableName(){
    if(strcmp(token,"select")==0){
        cout << "Illegal SELECT - Invalid table name" << endl;
        return 0;
    }
        
	if(strcmp(token,"from")==0){
		cout << "Illegal FROM - Invalid table name" << endl;
        return 0;
	}
	
	return 1;
}

char* getToken() {
    if(inputLine[index] == NULL) {
        index = 0;
        buffer[0]=0;
        return buffer;
    }

    /*if(inputLine[index] == "list") {
        
    }*/

    if(inputLine[index] == ',') {
        index++;
        buffer[0] = ',';
        buffer[1] = 0;
        return buffer;
    }

    while(isWhiteSpace(inputLine[index])) {
        index++;

        if(inputLine[index] == NULL) {
            index = 0;
            buffer[0]=0;
            return buffer;
        }
    }

    bufferIndex = 0;

    while(!isWhiteSpace(inputLine[index]) && inputLine[index] != NULL && inputLine[index] != ',') {
        buffer[bufferIndex] = tolower(inputLine[index]);

        index++;
        bufferIndex++;
    }
    
    buffer[bufferIndex]=0;
    return buffer;
}


void main() {

    cout << "John Clancy's Database Management System" << endl << endl;

    while(1) {
        cout << "Command: ";
        cin.getline(inputLine,64);
        index=0;
        
        token = getToken();

        if(strcmp(token,"")) {
            if(strcmp(token,"quit")==0) {
                break;
            }
        }

        cout << endl;

        parseSelect();

        cout << endl;
    }    
}

[CornedBee]

Is there any specific reason why you can't use an existing linked list? C doesn't have one in the standard library, but there must be a lot of implementations out there.

To get the commands into the buffer, use memcpy or strcpy or a similar function.

Edit: wait, this ain't the C board. Use a std::list of std::strings, for heaven's sake!

Oh, and don't use void main. See the FAQ for why.