This compiles in gcc with no errors or warnings even with -Wall option meaning that array bounds are checked at run-time and hence compiler can't detect the error
#include<stdio.h>
int main()
{
int a[2][3][4];
a[1][2][100] = 4 ;
return 0;
}
However,
#include<stdio.h>
int main()
{
int a[2][3];
a[1][2][100] = 4 ;
return 0;
}
this generates an error while compiling as :
$ gcc sample.c -Wall
sample.c: In function ‘main’:
sample.c:7: error: subscripted value is neither array nor pointer
Why is this so ? in both the two codes a[1][2][100] is invalid . Still how can the compiler detect this is code2 and not in code1.
Specially when every compiler flattens all multidimensional array into corresponding single dimension arrays, then how can the compiler be selectively aware of this flaw in the code.
Explanation or mention of some book or article where the proper explanation resides will be gratefully accepted :)
The difference is the types. C does no bounds checking but it does do (static) type checking. The type of a in your first example is int[][][] but the type in the second example is int[][].
The "flattening" that you refer to happens in code generation, which is (conceptually, at least) after type checking.