Lab46 Wiki

Following our exploration into nodes, linked lists, and groups of linked lists. From this point forward our node library has been restarted. We are recoding all the nodes and lists functions from start, but we are now moving into doubly linked nodes. Doubly linked nodes will further our learning into dealing with double pointers, passing by reference, and unions.

Once you grab dln0, you will find a new header file called data.h. In this header file, you will find a type of data called union:

union info {
    signed char value;
    struct node *data;
    void *other;
};

Furthermore, we have made some changes to our Node structure to include a pointer to left and right. It can be seen below:

struct node {
     union info     payload;
     struct node   *left;
     struct node   *right;
};

A union is a type of data that allows to store different types of data in the same memory location. A union can contain different members/properties, but only one member can contain a value at a time. Unions allocate the memory necessary to contain the largest member, the member with the type of data that requires the most memory.

If you recall from the sll project, info is the contents of the node. Info now has the potential to hold different types of data, not just an unsigned char, BUT it still only holds one at a time. The type of data it could hold is an unsigned char value, point to another Node anywhere else (could be in another group, on another list, so on), and a pointer that could point to any other type of pointer (only pointers though). In this project, we only need to worry about the node's left and right, and payload.

Remember that there can only be one return statement per function, I suggest having a variable that contains the exit code and change that along with the flow of the program in case of errors.

*Our task is to ask questions on Discord or in class and document our findings on this wiki page collaboratively, regarding the functionality of this project.

*For anybody interested in editing the wiki page, here is the dokuwiki user guide: https://www.dokuwiki.org/wiki:syntax#basic_text_formatting -Ash

dln0 has three different functions. These are:

mk.c
cp.c
rm.c

The general order you should complete them in is mk.c first, followed by rm.c, and cp.c last.

Some general advice for each function:
mknode() - don't forget about the left and right pointers, explore into /inc/ to see what each node contains
cpnode() - make sure to copy the entire payload, union has different types of different sizes so don't just copy the smallest one. It may be a good idea to use your previously created mk function. Remember, do not reinvent the wheel
rmnode() - not too much needed for this one, make sure you have the sufficient error checks, set to NULL after deallocation

1.Mknode
2.Rmnode
3.Cpnode

Useful tools for debugging issues are gdb and examining the test files themselves. to utilize gdb, run the test program with the gdb command (not make check), with a command that might look like “gdb ./bin/unit-lobtain”. Once in gdb the “run” command with start the program, and “break (line number)” will cause the program to stop at the specified line number. Once you have hit the breakpoint you can use “display (variable name)” to see the value of a variable at every step, “n” to step to the next line, and “continue” to continue running the program until the next breakpoint. Note that if you encounter a seg fault the program will tell the where the seg fault occurs, and you can use “run” again to restart the program.

All functions will return a status code, of type code_t. These codes will use bitwise operators, specifically the or operator.

Unit tests for this project are unit-mknode, unit-rmnode, and unit-cpnode. There are 33 total tests, 12 for mknode, 4 for rmnode, and 17 for cpnode. To get a general view of your entire project, run make check to see how many tests pass. To get a more detailed view of what tests are failing, ./bin/unit-(DESIRED_TEST). If you are getting segmentation faults, consider the use of gdb. If things aren't compiling correctly, it may be helpful to check the errors file as well.