Passing bidimensional arrays to function in C

pittopitto · 05-16-2006, 11:10 PM

Dear folks!!

I have a little problem. I can't pass bidimensional arrays to a function. I'll make an example: (code taken from a book)

Quote:

#include <stdio.h>

void printArray (const int a[][3]);

int main () {

int array1[2][3] = {{1,2,3},{4,5,6}};
int array2[2][3] = {1,2,3,4,5};
int array3[2][3] = {{1,2},{4}};

printf ("Values in array1 by row are:\n");
printArray(array1);

printf("Values in array2 by row are:\n");
printArray(array2);

printf("Values in array3 by row are:\n");
printArray(array3);

return 0;
}

void printArray (const int a[][3]) {

int i;
int j;

for (i=0; i<=1; i++) {

for (j=0; j<=2; j++) {

printf("%d ", a[i][j]);
}

}

}

Then I compile it with gcc:

Quote:

pitto@linux:~/Documents/C/Exercises> gcc -o matrix matrix.c
matrix.c: In function ‘main’:
matrix.c:12: warning: passing argument 1 of ‘printArray’ from incompatible pointer type
matrix.c:15: warning: passing argument 1 of ‘printArray’ from incompatible pointer type
matrix.c:18: warning: passing argument 1 of ‘printArray’ from incompatible pointer type
pitto@linux:~/Documents/C/Exercises>

What does it mean? I would like to pass a 2D array to a function, then modify it and then back to main.

Can you please help me???

Thanks in advance

pittopitto

paulsm4 · 05-16-2006, 11:17 PM

It's merely a warning - the code should still compile and run correctly.

A couple of interesting notes:
1. Microsoft VC++ doesn't even print the warning (Gcc does)
2. The thing it's complaining about is "const" (not the array dimensions)
3. To fix it, simply:
a) Eliminate "const" in your function signature
b) Cast it to "const" when you call your function
... or ...
c) Declare array1, array2 and array3 as "const"

leosgb · 05-16-2006, 11:20 PM

I am not sure why you are getting that but this is my output:

Code:

johndoe@zeus ~/bin $ gcc -Wall a.c 
a.c: In function `main':
a.c:8: warning: missing braces around initializer
a.c:8: warning: (near initialization for `array2[0]')
a.c:12: warning: passing arg 1 of `printArray' from incompatible pointer type
a.c:15: warning: passing arg 1 of `printArray' from incompatible pointer type
a.c:18: warning: passing arg 1 of `printArray' from incompatible pointer type
johndoe@zeus ~/bin $ ./a.out 
Values in array1 by row are:
1 2 3 4 5 6 Values in array2 by row are:
1 2 3 4 5 0 Values in array3 by row are:
1 2 0 4 0 0 johndoe@zeus ~/bin $

I just copy and pasted your code. No modifications.

pittopitto · 05-17-2006, 01:01 AM

Dear folks,

I executed the code after compilation and it's working.
About the output, I just forgot to put a newline!!
Sorry!!

Pitto

leosgb · 05-17-2006, 10:21 AM

good to hear that

ta0kira · 05-18-2006, 09:31 AM

Maybe 'const int &a[][3]' or 'const int *a[3]' would get rid of the warning...
ta0kira