Reading file content line by line into a matrix - c

Question

I was trying to write a function that could copy a text file content line by line to a matrix, so this is what I came up with:
#include <stdio.h>
#include <stdlib.h>
#define rows 5
#define columns 12
void file_to_matrix(char *matrix[]){
FILE *file = fopen("swamp.txt", "r");
if(file==NULL){
printf("File error");
exit(1);
}
int y=0;
for(int x=0; (matrix[y][x]=fgetc(file))!=EOF; ++x){
if(matrix[y][x]=='\n'){
++y;
x=0;
}
}
fclose(file);
}
int main(){
char *matrix[rows];
file_to_matrix(matrix);
for(int i=0; i<5; ++i){
for(int j = 0; j < 11; j++){
printf("%c", matrix[i][j]);
}
printf("\n");
}
}
I tried to compile and run it on Windows and Linux but the only thing that it manages to do is giving me errors that are practically useless like:
"Stopping due to fatal error: NullReferenceException: Object reference not set to an instance of an object"
or
"Segmentation fault (core dumped)"

Answer 1

You have to allocate memory for each element of matrix. This is the same exact mistake as writing:
char *s = "string";
As the first act of the program, loop through matrix, and call malloc for each cell:
int i;
for (i = 0; i < 5; ++i)
if (!(matrix[i] = malloc(MAXLEN))) [
perror("malloc");
exit(EXIT_FAILURE);
}
Note: we check the return value of malloc to ensure no errors have occurred.

Answer 2

with your code, i think the matrix in the file will restricted (you define rows=5 and columns=12). so i think again to write a code that can be flexible, no need to set max row or column again. here we go
#include <stdio.h>
#include <stdlib.h> //malloc realloc
//file read function. returning string with splitted new line
//ex: (note: newline is '\n' (ENTER))
//test.txt:
//10 20 30(space)(newline)
//40 50 60(space)(newline)
void file_to_matrix(char *filename)
{
FILE * file = fopen(filename, "r");
char *buff = (char*)malloc(sizeof(char)); //temp string
int *matrix_row = (int*)malloc(sizeof(int)); //temp matrix row
int **MATRIX = (int**)malloc(sizeof(int*)); //this will become the final matrix
int index_buff = 0, index_MATRIX = 0, index_matrix_row = 0;
while (1)
{
char c = getc(file);
if (c==EOF)
{
break;
}
if (c=='\n') //if c meet newline, then add the matrix row to final matrix
{
(*(MATRIX+index_MATRIX)) = matrix_row;
index_MATRIX++;
MATRIX = realloc(MATRIX, sizeof(MATRIX)*(index_MATRIX+1));
matrix_row = (int*)malloc(sizeof(int));
index_matrix_row = 0;
printf("\n");
continue;
}
if (c==' ') //if c meet space, then buff wil converted to int
{
int num = atoi(buff);
printf("%d ", num);
(*(matrix_row+index_matrix_row)) = num;
index_matrix_row++;
matrix_row = realloc(matrix_row, sizeof(int)*(index_matrix_row+1));
free(buff);
buff = (char*)malloc(sizeof(char));
index_buff=0;
continue;
}
//add buff with c
(*(buff+index_buff))=c;
index_buff++;
buff = realloc(buff, sizeof(char)*(index_buff+1));
}
fclose(file);
//clearing the dynamic memory
free(buff);
for (int i = 0; i < index_MATRIX; i++)
{
free(MATRIX[i]);
}
}
int main()
{
file_to_matrix("test.txt");
return 0;
}
test.txt:
10 20 30
40 50 60
70 80 90
if you confused with the test.txt format, i will explain again:
10 20 30(space)(newline)
30 40 60(space)(newline)
70 80 90(space)(newline)

Answer 3

Thank you for your replies, I think your solutions are very clever but I was looking to an easier one.
After a little bit of trial and error I think I found a solution that it isn't very generalized but it's simple and it seems to work fine:
#include <stdlib.h>
#include <stdio.h>
#define ROWS <n of rows>
#define COLS <n of columns>
void file_to_matrix(int rows, int cols, char matrix[rows][cols], char file_path[]){
FILE *file = fopen(file_path, "r");
if(file==NULL){
printf("File error");
exit(1);
}
int y=0;
for(int x=0; (matrix[y][x]=getc(file))!=EOF; ++x){
if(matrix[y][x]=='\n'){
matrix[y][x]='\0';
++y;
x=-1;
}
}
fclose(file);
}
int main(){
char matrix[ROWS][COLS+2];
file_to_matrix(ROWS, COLS+2, matrix, "file path");
for(int i=0; i<=ROWS; ++i){
printf("%s\n", matrix[i]);
}
}
Thank you again for your answers