Thread: passing 2d char array to a function

I know how to pass in 2d char arrays if i'm dealing with the first dimension of the array:

Code:

void fromAbove(char array[],int row)
{
        char temp;

        temp = array[row];
        array[row] = array[row - 1];
        array[row - 1] = temp;
}

and that to return that in the main function, I use the array I want as input, and put the second dimension in:

Code:

 fromAbove(puzzle[column],row);

but I have absolutely no idea how to do that when I refer only to the second dimension. Other posts I read say that I need to define the length of the second dimension, but I don't know if I can do that since I think I'd need a for loop inside the function and all I need to do is run the function when a certain value is found within the original 2d array.

If it helps, the program is one of those 5x5 puzzles (read using file i/o, printed to another file after functions are run on it) with a space in it where you slide around pieces until you get a picture. Except this is with letters, and instead of solving it, I'm just writing a program that runs a number of moves on it.

EX:

TRGSJ
XDOKI
M VLN
WPABE
UQCHF
ARRBBL

where line 6 is the line of instructions for what moves to make. I have the functions written for moves that involve moving the space up or down, but can't figure out moving right and left. I know I need to do a [column + 1] and a [column - 1], but have no idea how to pass the array into a function.

Thanks for your time =]

What you actually want to do is pass a pointer to the memory holding your 2D array. In C, we typically don't want to pass large, contiguous regions of data by value since it is inefficient, so we pass their locations (addresses) instead.

Code:

void fromAbove(char* array[], int rows)

char* array[] is a pointer to an array or arrays of characters. Since each array of characters
is, by C convention, terminated by a null character, we only have to tell the function how many rows there are so long as we're mindful about not reading or writing past these nulls.

To access an element in row R and column C of this 2D array, use "array[R][C]".

I understand why pointers would be useful, and I experimented with them earlier, but unless I was using them completely incorrectly, I didn't find it that useful in creating the output I wanted. I figured that might have been due to the fact that instead of returning an entire array from the function, I'm only applying the function to one specific instance:

Code:

if(puzzle[row][column] == ' ')
{
     fromAbove(puzzle[column],row);
}

Originally Posted by kittykitty

To access an element in row R and column C of this 2D array, use "array[R][C]".

For this part of your post, I don't quite understand what you're saying...would this be in the function or where I call it? If I use it in the function definition I'll get a compiler error stating that R and C are undeclared variables. If you're referring to just referencing the value in the array specifically, that part I have covered for the most part; I just need to know how to reference the second dimension [column] in a function definition and how to call it, since the first dimension [row] is a constant for the stated situations.

Originally Posted by kmdv

Code:

if(puzzle[row][column] == ' ')
{
     fromAbove(puzzle[column],row);
}

Decide whether the first dimension is row or column. Assuming columns are the first dimension, you cannot generate a pointer pointing to a row. You should pass pointer to all the elements.

the call for the function is standard when in the function you deal with the first dimension. if you look at the OP, when i write the code for the function, it reads as

Code:

void fromAbove(char array[],row)

in that sense, i've already decided row as first dimension and column as second.

in regards to pointers, another method i tried was

Code:

void fromAbove(char array[5][5]) //don't remember if i defined any variables after that

//back in the main function, the call looks like:
fromAbove(**puzzle);

however, that assumes i want to change both dimensions, which i do not.