How to pass a 2-dimensional array to a C function

Question

This is my code in plain old C. I want to add each column of the data. For example, 28+518+917, 34+512+914, et.al.:

short rawdata[][20]={
28,34,36,39,42,47,37,41,41,33,33,36,36,36,27,27,24,31,29,26,
518,512,507,508,521,522,524,525,519,512,506,511,511,501,501,495,497,500,508,504,
917,914,905,909,892,879,869,873,876,877,875,870,883,893,893,884,881,882,885,888
};

int aae( int nLenFrame, short **psDataBuffer, float *pFV )
{
    float sum = 0.0;
    int i=0, j;
    for (j=0; j<AXES; j++)
    {
        printf("Component: %d\n", *(*(psDataBuffer +j) + i));
    }
    return 1;
}


int main(int argc, char *argv[]){
    int arraySize;
    float pFV;
    int a;

    arraySize = sizeof(rawdata)/sizeof(int);
    a = aae( arraySize, rawdata, &pFV );
    printf("aae = %f\n", pFV);
}

I'm trying to pass rawdata to function aae but when I compile, I get the following errors/warnings from gcc, which naturally, crash my code. How should I pass rawdata into aae?

$ gcc aae.c -o aae
aae.c: In function ‘main’:
aae.c:31:2: warning: passing argument 2 of ‘aae’ from incompatible pointer type [enabled by default]
  a = aae( arraySize, rawdata, &pFV );
  ^
aae.c:13:5: note: expected ‘short int **’ but argument is of type ‘short int (*)[20]’
 int aae( int nLenFrame, short **psDataBuffer, float *pFV )
     ^

Thanks in advance for any help.

Answer 1

I answer this as an XY problem, as you want to sum the columns, and in doing so hit other problems, which you ask how to solve. But also answers from incomplete information which I have to guess.

You declared a 2D array short rawdata[][20] but supplied data as if it is a 1D array. You then fiddle with pointers and come up with a wrong answer.

This answer initialises a 2D array correctly, and sums the columns simply, by using array indexing.

#include <stdio.h>

#define AXES 3
#define COLS 20

short rawdata[AXES][COLS]={
    {28,34,36,39,42,47,37,41,41,33,33,36,36,36,27,27,24,31,29,26 },
    {518,512,507,508,521,522,524,525,519,512,506,511,511,501,501,495,497,500,508,504},
    {917,914,905,909,892,879,869,873,876,877,875,870,883,893,893,884,881,882,885,888}
};

void sumcols(short rawdata[][COLS]) {
    int col, axis;
    float sum;

    for (col=0; col<COLS; col++) {
        sum = 0;
        for (axis=0; axis<AXES; axis++) {
            sum += rawdata [axis][col];
        }
        printf("Column %2d sum = %f\n", col, sum);
    }
}

int main(void) {
    sumcols(rawdata);
    return 0;
}

Program output:

Column  0 sum = 1463.000000
Column  1 sum = 1460.000000
Column  2 sum = 1448.000000
Column  3 sum = 1456.000000
Column  4 sum = 1455.000000
Column  5 sum = 1448.000000
Column  6 sum = 1430.000000
Column  7 sum = 1439.000000
Column  8 sum = 1436.000000
Column  9 sum = 1422.000000
Column 10 sum = 1414.000000
Column 11 sum = 1417.000000
Column 12 sum = 1430.000000
Column 13 sum = 1430.000000
Column 14 sum = 1421.000000
Column 15 sum = 1406.000000
Column 16 sum = 1402.000000
Column 17 sum = 1413.000000
Column 18 sum = 1422.000000
Column 19 sum = 1418.000000