I have a two dimensional array of pointers declared in main as
char* data[3][8]
which I passed into a function
void func(char*** data)
When I did printf("%p\n", data[0]); in main and in the function I got different outputs 0x7ffeabc27640 in main and (nil) in the function. Albeit printing just data outputs the same address with that from inside the main. Why can't I access the array in the function.
If you enable some warnings (which you should always do), you'll get :
main.cpp: In function 'main':
main.cpp:6:10: warning: passing argument 1 of 'func' from incompatible pointer type
func(data);
^
main.cpp:2:6: note: expected 'char ***' but argument is of type 'char * (*)[8]'
void func(char*** data) { (void)data; }
^
Which tells you exactly what's wrong, namely that an array is not a pointer. Dereferencing a pointer that has been converted to the wrong type is undefined behaviour, so you can get anything back.
Have your function take in a char *(*)[8] if you want to give it a char *(*)[8] :
void func(char *(*data)[8]);
Or, if you want to emphasize that data should point to the first element of an array :
void func(char *data[][8]);
The two syntaxes are perfectly equivalent.
Note : the file is named main.cpp but is indeed compiled in C mode.
foo(char* bar[3][8]); or foo(char* bar[][8]);. If you choose to use the second one, you could also pass the number of elements (of your array's first dimension) as second parameter of the function as @Neil suggested.
foo(char* bar[][8]) is sugar for foo(char *(*bar)[8]), though. I'm keeping this answer as a minimal solution to the actual error, Neil has dug up a great demonstration and there's no point repeating it.Passing 2D arrays to a function -
This will help you read-up and better understand how to do this...
http://www.geeksforgeeks.org/pass-2d-array-parameter-c/
The below is a snippet from the web-page - showing one example of how to do this.
#include <stdio.h>
const int n = 3;
void print(int arr[][n], int m)
{
int i, j;
for (i = 0; i < m; i++)
for (j = 0; j < n; j++)
printf("%d ", arr[i][j]);
}
int main()
{
int arr[][3] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
print(arr, 3);
return 0;
}
Output:
1 2 3 4 5 6 7 8 9
char ***.