2D array in by reference - c

Question

I have this...
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
//definições de constantes usadas para agilizar a implementação.
#define MINA 'M'
#define SUB 'S'
#define JOG 'U'
#define CC 'I'
//Função que inicializa posição do jogador.
void posjog(char **mesa,int lin, int col){
srand(time(NULL));
int i = rand() % 2;
int j = rand() % 2;
if(i==1){
i = lin;
}
if(j==1){
j = col;
}
mesa[i][j] = JOG;
}
//Função que inicializa a matriz vazia.
void arfill(char **mesa,int lin, int col){
for(int i=0;i<=lin;i++){
for(int j=0;j<=col;j++){
mesa[i][j]='.';
}
}
}
void show(char **mesa,int lin,int col){
for(int i=0;i<=lin;i++){
for(int j=0;j<=col;j++){
printf("%c",mesa[i][j]);
}
printf("\n");
}
}
int main(void) {
char campo[9][9]; //matriz de jogo
arfill(campo,9,9);
posjog(campo,9,9);
show(campo,9,9);
return EXIT_SUCCESS;
}
My code always crashes, i dunno why.
Can some of you please help me with this?
I have some Warnings on the Eclipse too...
"passing argument 1 of 'arfill' from incompatible pointer type [enabled by default]"
"expected 'char **' but argument is of type 'char (*)[9]'"

Answer 1

Array indexing starts from 0 and ends in size of array - 1.
So, this
for(int i=0;i<=lin;i++){
for(int j=0;j<=col;j++){
will go from 0 to 9 for an array of size 9x9, thus it will go out of bounds.
Similarly the rest of the code has similar problems.
You should definitely enable the warning of your compiler (-Wall flag would suffice for a start). Warnings are good to be treated like errors by us. Here is what I got:
../main.c: In function ‘main’:
../main.c:45:5: warning: passing argument 1 of ‘arfill’ from incompatible pointer type [enabled by default]
../main.c:26:6: note: expected ‘char **’ but argument is of type ‘char (*)[9]’
../main.c:46:5: warning: passing argument 1 of ‘posjog’ from incompatible pointer type [enabled by default]
../main.c:12:6: note: expected ‘char **’ but argument is of type ‘char (*)[9]’
../main.c:47:5: warning: passing argument 1 of ‘show’ from incompatible pointer type [enabled by default]
../main.c:34:6: note: expected ‘char **’ but argument is of type ‘char (*)[9]’
Finished building: ../main.c
So one way to deal with this is to use define for the sizes of the matrix. Then your code should look like this:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
//definições de constantes usadas para agilizar a implementação.
#define MINA 'M'
#define SUB 'S'
#define JOG 'U'
#define CC 'I'
#define N 9
#define M 9
//Função que inicializa posição do jogador.
void posjog(char mesa[N][M]) {
srand(time(NULL));
int i = rand() % 2;
int j = rand() % 2;
if (i == 1) {
i = N;
}
if (j == 1) {
j = M;
}
// if i and j have the value of N and M, this will go out of bounds
// mesa[i][j] = JOG; <---- modify this
}
//Função que inicializa a matriz vazia.
void arfill(char mesa[N][M]) {
// Replaces <= with < in both for loops
for (int i = 0; i < N; i++) {
for (int j = 0; j < M; j++) {
mesa[i][j] = '.';
}
}
}
void show(char mesa[N][M]) {
// Replaces <= with < in both for loops
for (int i = 0; i < N; i++) {
for (int j = 0; j < M; j++) {
printf("%c", mesa[i][j]);
}
printf("\n");
}
}
int main(void) {
char campo[N][M]; //matriz de jogo
arfill(campo);
posjog(campo);
show(campo);
return EXIT_SUCCESS;
}
Of course you could dynamically allocate the memory for the array, which would get rid of the define. In that case don't forget to de-allocate your memory.