% cat so30681402.c
#include <stdio.h>

int main(void) {
    int za[0];
    printf("sizeof array with no elements is %d.\n", (int)sizeof za);
    return 0;
}

% clang -std=c99 -pedantic -Weverything so30681402.c
so30681402.c:4:12: warning: zero size arrays are an extension
      [-Wzero-length-array]
    int za[0];
           ^
1 warning generated.

% ./a.out
sizeof array with no elements is 0.
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