C dynamic 2d Matrices struct frustration - arrays

Question

I searched all over the internet and watched tons of video and nobody does this thing :
Create a struct matrix that can dynamicly change its KxN direct from the main , for example
I will use java :
Matrix(int k , int n){
int Mat[k][n];
}
main(){
Matrix a = new Matrix (2,3);
a.Mat[0][0] = 1;
syso(a.Mat[0][0]);
}
Im begining to think its imposible , I tried to alocate memory from the main and it worked , this is how I did it
int** arr = malloc(sizeof(int*)*n)
for (int i = 0 ; i < k ; i=+){
arr[i] = malloc(sizeof(int)*3);
}
but the problem is I cannot do it inside a struct for some reason .. I need to keep my main clean so all my work should be done above the main ,
this is my C program that doesn't work :
//__________________HEADER_________________________________________________//
#include <stdio.h>
#include <stdlib.h>
//__________________________________________________________________________//
//__________________OBJECTS______________________________________________________//
typedef struct {
int n , k ;
int** Mat;
}Matrix;
//______________________________________________________________________________//
//___________________MAIN_____________________________________________________//
int main (void) {
printf("Start..\n\n");
Matrix aqq = {2,5} ;
aqq.Mat[0][0] = 5 ;
printf("\n size : %dx%d first element : %d \n",aqq.n , aqq.k , aqq.Mat[0][0]);
printf("\n\nEnd\n");
}
//______________________________________________________________________________//
I need to make all the getters and setter mult transpose all the matrices functions including linear copying guassian elemination .. everything and I would like to receive maybe a link to some guide lines or even a book , I don't care as long as I could study from it because its really difficult to work like that there are too many rules that involves memory and not a single reliable source of information because every body doing the easy stuff on the tutorials
so to sum up , the final goal is to control every function completely through the main

Answer 1

Here's code that could be split into three files — matrix.h, matrix.c and test.matrix.c.
The header matrix.h declares an opaque type Matrix and some functions to manipulate that type — a constructor (the third option in my comment), a destructor, routines to get and set element values, and routines to get the array dimensions.
The implementation file matrix.c defines the functions. It uses assertions to ensure the validity of arguments — lazy but effective as long as you never compile with -DNDEBUG. If you do suppress assertions, you need to put proper error handling into the functions. Deciding how to handle errors detected by corrupted data structures is a project-wide decision. The code is careful to free any already allocated memory if there is an allocation failure during the construction of a matrix. It defines the struct Matrix, but that type is not accessible outside this source file.
The test file test.matrix.c provides some code to use all the functions declared in matrix.h and demonstrates that square and rectangular matrices work. The code in this file cannot dereference the matrix structure; it must use the access functions.
The resulting code is quite big, but it does the job and demonstrates that you can indeed use structures to store matrices. Write a matrix multiplication routine is a simple exercise.
/* SOF - matrix.h */
#ifndef MATRIX_H_INCLUDED
#define MATRIX_H_INCLUDED
#include <stddef.h> /* size_t */
enum { MATRIX_MAX_SIZE = 1000 };
typedef struct Matrix Matrix; /* Opaque type */
extern Matrix *matrix_constructor(size_t rows, size_t cols);
extern void matrix_destructor(Matrix *mtx);
extern int matrix_get_element(const Matrix *mtx, size_t r, size_t c);
extern void matrix_set_element(Matrix *mtx, size_t r, size_t c, int v);
extern size_t matrix_get_cols(const Matrix *mtx);
extern size_t matrix_get_rows(const Matrix *mtx);
#endif /* MATRIX_H_INCLUDED */
/* EOF - matrix.h */
/* SOF - matrix.c */
/*#include "matrix.h"*/
#include <assert.h>
#include <stdlib.h>
struct Matrix
{
size_t rows;
size_t cols;
int **data;
};
/* It is important to prevent memory leaks on allocation failure */
Matrix *matrix_constructor(size_t rows, size_t cols)
{
assert(rows <= MATRIX_MAX_SIZE && rows > 0);
assert(cols <= MATRIX_MAX_SIZE && cols > 0);
Matrix *mtx = malloc(sizeof(*mtx));
if (mtx == NULL)
return NULL;
mtx->data = malloc(sizeof(*mtx->data) * rows);
if (mtx->data == NULL)
{
free(mtx);
return NULL;
}
for (size_t i = 0; i < rows; i++)
{
mtx->data[i] = malloc(sizeof(*mtx->data[i]) * cols);
if (mtx->data[i] == NULL)
{
while (i > 0)
free(mtx->data[--i]);
free(mtx);
return NULL;
}
}
mtx->rows = rows;
mtx->cols = cols;
return mtx;
}
void matrix_destructor(Matrix *mtx)
{
assert(mtx != NULL && mtx->data != NULL);
assert(mtx->rows <= MATRIX_MAX_SIZE && mtx->rows > 0);
assert(mtx->cols <= MATRIX_MAX_SIZE && mtx->cols > 0);
for (size_t i = 0; i < mtx->rows; i++)
free(mtx->data[i]);
free(mtx->data);
free(mtx);
}
int matrix_get_element(const Matrix *mtx, size_t r, size_t c)
{
assert(mtx != NULL && mtx->data != NULL);
assert(mtx->rows <= MATRIX_MAX_SIZE && mtx->rows > 0);
assert(mtx->cols <= MATRIX_MAX_SIZE && mtx->cols > 0);
return mtx->data[r][c];
}
void matrix_set_element(Matrix *mtx, size_t r, size_t c, int v)
{
assert(mtx != NULL && mtx->data != NULL);
assert(mtx->rows <= MATRIX_MAX_SIZE && mtx->rows > 0);
assert(mtx->cols <= MATRIX_MAX_SIZE && mtx->cols > 0);
mtx->data[r][c] = v;
}
size_t matrix_get_rows(const Matrix *mtx)
{
assert(mtx != NULL && mtx->data != NULL);
assert(mtx->rows <= MATRIX_MAX_SIZE && mtx->rows > 0);
assert(mtx->cols <= MATRIX_MAX_SIZE && mtx->cols > 0);
return mtx->rows;
}
size_t matrix_get_cols(const Matrix *mtx)
{
assert(mtx != NULL && mtx->data != NULL);
assert(mtx->rows <= MATRIX_MAX_SIZE && mtx->rows > 0);
assert(mtx->cols <= MATRIX_MAX_SIZE && mtx->cols > 0);
return mtx->cols;
}
/* EOF - matrix.c */
/* SOF - test.matrix.c */
/*#include "matrix.h"*/
#include <errno.h>
#include <stdarg.h>
#include <stdint.h> /* intmax_t */
#include <stdio.h>
/*#include <stdlib.h>*/
#include <string.h>
#include <time.h>
/* Cannot dereference Matrix pointers here! */
static void matrix_print(const char *tag, const Matrix *mtx, int width)
{
size_t rows = matrix_get_rows(mtx);
size_t cols = matrix_get_cols(mtx);
printf("%s (%zux%zu):\n", tag, rows, cols);
for (size_t r = 0; r < rows; r++)
{
const char *pad = "";
for (size_t c = 0; c < cols; c++)
{
printf("%s%*d", pad, width, matrix_get_element(mtx, r, c));
pad = ", ";
}
putchar('\n');
}
}
static void matrix_random(Matrix *mtx)
{
size_t rows = matrix_get_rows(mtx);
size_t cols = matrix_get_cols(mtx);
for (size_t r = 0; r < rows; r++)
{
for (size_t c = 0; c < cols; c++)
matrix_set_element(mtx, r, c, (rand() % (rows * cols) + 1));
}
}
static int i_log10(size_t n)
{
if (n < 10)
return 1;
int c = 1;
while (n >= 10)
{
n /= 10;
c++;
}
return c;
}
static int i_pow10(int n)
{
int r = 1;
while (n-- > 0)
r *= 10;
return r;
}
static void matrix_ordered(Matrix *mtx)
{
size_t rows = matrix_get_rows(mtx);
size_t cols = matrix_get_cols(mtx);
int mul = i_pow10(i_log10(cols));
for (size_t r = 0; r < rows; r++)
{
for (size_t c = 0; c < cols; c++)
matrix_set_element(mtx, r, c, (r + 1) * mul + c + 1);
}
}
static void err_exit(const char *fmt, ...)
{
va_list args;
int errnum = errno;
va_start(args, fmt);
vfprintf(stderr, fmt, args);
if (errnum != 0)
fprintf(stderr, " (%d: %s)", errnum, strerror(errnum));
putc('\n', stderr);
exit(EXIT_FAILURE);
}
static Matrix *matrix_checked_constructor(const char *tag, size_t rows, size_t cols)
{
Matrix *mp = matrix_constructor(rows, cols);
if (mp == NULL)
err_exit("Failed to construct matrix %s", tag);
return mp;
}
int main(void)
{
Matrix *mi5 = matrix_checked_constructor("MI5", 5, 5);
Matrix *mi6 = matrix_checked_constructor("MI6", 6, 6);
Matrix *ks69 = matrix_checked_constructor("KS69", 6, 9);
Matrix *bw1815 = matrix_checked_constructor("BW1815", 18, 15);
time_t now = time(0);
srand(now);
printf("Seed: %jd\n", (intmax_t)now);
matrix_random(mi5);
matrix_random(mi6);
matrix_ordered(ks69);
matrix_ordered(bw1815);
matrix_print("MI5", mi5, 2);
matrix_print("MI6", mi6, 2);
matrix_print("KS69", ks69, 3);
matrix_print("BW1815", bw1815, 4);
matrix_destructor(mi5);
matrix_destructor(mi6);
return 0;
}
/* EOF - test.matrix.c */
Example output:
Seed: 1605897737
MI5 (5x5):
14, 22, 5, 21, 11
23, 5, 23, 7, 2
10, 9, 9, 2, 24
10, 6, 21, 6, 11
5, 11, 5, 18, 3
MI6 (6x6):
25, 33, 4, 18, 24, 19
6, 1, 23, 19, 6, 24
17, 2, 26, 3, 2, 32
7, 34, 8, 5, 11, 33
6, 7, 34, 13, 21, 14
15, 25, 32, 11, 28, 28
KS69 (6x9):
11, 12, 13, 14, 15, 16, 17, 18, 19
21, 22, 23, 24, 25, 26, 27, 28, 29
31, 32, 33, 34, 35, 36, 37, 38, 39
41, 42, 43, 44, 45, 46, 47, 48, 49
51, 52, 53, 54, 55, 56, 57, 58, 59
61, 62, 63, 64, 65, 66, 67, 68, 69
BW1815 (18x15):
101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115
201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215
301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 311, 312, 313, 314, 315
401, 402, 403, 404, 405, 406, 407, 408, 409, 410, 411, 412, 413, 414, 415
501, 502, 503, 504, 505, 506, 507, 508, 509, 510, 511, 512, 513, 514, 515
601, 602, 603, 604, 605, 606, 607, 608, 609, 610, 611, 612, 613, 614, 615
701, 702, 703, 704, 705, 706, 707, 708, 709, 710, 711, 712, 713, 714, 715
801, 802, 803, 804, 805, 806, 807, 808, 809, 810, 811, 812, 813, 814, 815
901, 902, 903, 904, 905, 906, 907, 908, 909, 910, 911, 912, 913, 914, 915
1001, 1002, 1003, 1004, 1005, 1006, 1007, 1008, 1009, 1010, 1011, 1012, 1013, 1014, 1015
1101, 1102, 1103, 1104, 1105, 1106, 1107, 1108, 1109, 1110, 1111, 1112, 1113, 1114, 1115
1201, 1202, 1203, 1204, 1205, 1206, 1207, 1208, 1209, 1210, 1211, 1212, 1213, 1214, 1215
1301, 1302, 1303, 1304, 1305, 1306, 1307, 1308, 1309, 1310, 1311, 1312, 1313, 1314, 1315
1401, 1402, 1403, 1404, 1405, 1406, 1407, 1408, 1409, 1410, 1411, 1412, 1413, 1414, 1415
1501, 1502, 1503, 1504, 1505, 1506, 1507, 1508, 1509, 1510, 1511, 1512, 1513, 1514, 1515
1601, 1602, 1603, 1604, 1605, 1606, 1607, 1608, 1609, 1610, 1611, 1612, 1613, 1614, 1615
1701, 1702, 1703, 1704, 1705, 1706, 1707, 1708, 1709, 1710, 1711, 1712, 1713, 1714, 1715
1801, 1802, 1803, 1804, 1805, 1806, 1807, 1808, 1809, 1810, 1811, 1812, 1813, 1814, 1815