CODEWITHSUNDEEP
carrayspointers
Gleiry Agustin Serrano Wong
Gleiry Agustin Serrano Wong

Reputation: 73

Pass Arbitrary Sized 2 Dimension Array

Hi I am studying about sorting algorithms, for that I want to make a simple program for getting an array of integers from a text file. While doing that I'm having some trouble and questions regarding arrays and functions that take them as parameters . Here is what I do:

#include<stdio.h>
#include<stdlib.h>

#define MAX_SIZE 64
#define MAX_INT_SIZE 10000

void itobuff(const char* istring,const int** sint);
int getistring(FILE* file,char strbuffer[][MAX_SIZE],int max_int,int max);

int main(int argc,char*argv[]){

   char buffer[MAX_INT_SIZE][MAX_SIZE];

   int int_counter=0;
   int int_buffer[MAX_INT_SIZE];

    FILE *file = fopen("MYFILE.txt","r");

    getistring(file,buffer,MAX_INT_SIZE,MAX_SIZE);


    return 0;

}

My doubt is about the definition of the function 

int getistring(FILE* file,char strbuffer[][MAX_SIZE],int max_int,int max);

I want to write a function which allows to use any size array. I know this is wrong, but logically it is what I want to achieve but can't figure out how. 

 int getistring(FILE* file,char strbuffer[][],int max_int,int max);

I know that what I want to do may be done in some other way but I want to know how to do it. For example if I want to write a function that gets an array and returns the determinant of that array, you shouldn't be forced to restrict yourself to a k size array. Or more generally to a i-columns,j-rows array for any other array operation.

Upvotes: 2

Views: 181

Answers (2)

paddy
paddy

Reputation: 63481

Two-dimensional arrays are actually laid out in one dimension. The reason you need to provide the step-size is so the compiler knows how to multiply indices to make a linear index. If you want to use arbitrary sized arrays, use a 1-D array and provide a step size.

Consider this:

char strbuffer[][MAX_SIZE];

The compiler knows that to get an element at strbuffer[i][j], it must use:

strbuffer + i * MAX_SIZE + j;

Notice that I've used strbuffer as if it was a pointer. You're allowed to do this - the compiler will convert an array into a pointer as a convenience.

So, redefine your function to take a 1D array, and use the computation above. If you're not already passing the step size (or width, or whatever you call it), then add that as a paramter:

int getistring(FILE* file, char strbuffer[], int max_int, int max);

Upvotes: 0

Eric Postpischil
Eric Postpischil

Reputation: 223493

If you are using a C implementation that supports C 1999, then it supports variable-length arrays.

Declare a function that takes a variable-length array parameter like this:

int getistring(FILE *file, size_t Rows, size_t Columns, char buffer[][Columns]);

Call the function like this:

result = getistring(file, Rows, Columns, buffer);

Create the buffer array like this:

size_t Rows = some calculation for number of rows;
size_t Columns = some calculation for number of columns;
char (*buffer)[Columns] = malloc(Rows * sizeof *buffer);
if (!buffer)
     Handle error.

When done, free the buffer array like this:

free(buffer);

If the numbers of rows and columns are small, you can define the buffer array with automatic storage instead of using malloc and free, like this:

char buffer[Rows][Columns];

Upvotes: 3

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