Read file into multidimensional character array in C - c

Question

I am trying to read a Multidimensional String Matrix from a file and store it to a array of Character Arrays like this:
char *A[M][N];
This works fine if I stay inside the main function.
But when i am trying to call a function by reference it doesn't work.
Function Call:
readMatrix(file,A);
Function Header:
int readMatrix(FILE *file,char *matrix[][]);
I also tried this:
int readMatrix(FILE *file,char ***matrix);
which also doesn't work.
I want to manipulate the Array in the function therefore i need to make a reference call.

Answer 1

You must pass N as part of the matrix type to your ReadMatrix function, and since it is not known at compile time, you must pass these as arguments too:
int readMatrix(FILE *file, size_t M, size_t N, char *matrix[][N]);
You could indeed also specify the array argument as char *matrix[M][N], but the first dimension size M is ignored for a function argument as it only receives a pointer to the array.
Here is an example:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int readMatrix(FILE *file, size_t rows, size_t cols, char *matrix[][cols]) {
int rc = 0;
for (size_t i = 0; i < rows; i++) {
for (size_t j = 0; j < cols; j++) {
char buf[80];
if (rc == 0 && fscanf(file, "%79s", buf) == 1) {
matrix[i][j] = strdup(buf);
} else {
matrix[i][j] = NULL;
rc = -1;
}
}
}
return rc;
}
int main(void) {
size_t rows, cols;
if (scanf("%zu %zu", &rows, &cols) != 2)
return 1;
char *mat[rows][cols];
if (readMatrix(stdin, rows, cols, mat) == 0) {
for (size_t i = 0; i < rows; i++) {
for (size_t j = 0; j < cols; j++) {
printf(" %8s", mat[i][j]);
}
printf("\n");
}
}
for (size_t i = 0; i < rows; i++) {
for (size_t j = 0; j < cols; j++) {
free(mat[i][j]);
}
}
return 0;
}

Answer 2

You can do it by using this approach:
#include <stdio.h>
#define MAX_WORD_SIZE 10
void readMatrix(FILE*,char****);
int main(void){
FILE* cin = fopen("input.txt","r");
char*** inputMatrix;
readMatrix(cin,&inputMatrix);
for(int i=0;i<3;i++){
for(int j=0;j<3;j++){
printf("%s ",*(*(inputMatrix+i)+j));
}
printf("\n");
}
fclose(cin);
return 0;
}
void readMatrix(FILE* cin,char**** matrix){
int rowNum,columnNum;
char buff[10];
int intBuff;
fscanf(cin,"%d",&intBuff);
rowNum = intBuff;
fscanf(cin,"%d",&intBuff);
columnNum = intBuff;
*matrix = malloc(rowNum*sizeof(char**));
for(int i=0;i<rowNum;i++){
*(*matrix+i) = malloc(columnNum*sizeof(char*));
}
for(int i=0;i<rowNum;i++){
for(int j=0;j<columnNum;j++){
*(*(*matrix+i)+j) = malloc(MAX_WORD_SIZE*sizeof(char));
fscanf(cin,"%s",*(*(*matrix+i)+j));
}
}
}
with this input file(input.txt file within same folder), this code is working well on Linux GCC
3 3
ab cd ef
gh ij kl
mn op qr
In the first line of input.txt file, first integer denotes row number, second integer denotes column number.