Question

my code:

#include <iostream>
using namespace std;
int main() {
    int n=5;
    int a[n][n];
    a[1][1]=5;
    return 0;
}

I got this error when trying to watch the expression a[1][1] in eclipse on line 6:

Failed to execute MI command:
-data-evaluate-expression a[1][1] Error message from debugger back end:
Cannot perform pointer math on
incomplete types, try casting to a
known type, or void *.

i guess it’s returned from gdb? however, i don’t know why i can’t watch that value? Isn’t “a” is a normal multi-dimensional array?

Answer 1

For some odd reasons this isn’t valid C++ unless you make it

const int n = 5;

Otherwise the array size is formally unknown until runtime.