Question

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In C arrays why is this true? a[5] == 5[a]
C weird array syntax in multi-dimensional arrays

Today I came across this blog. What attracted me the most is this:

int i;
i["]<i;++i){--i;}"];

Well, I don’t really know what is the purpose of the weird “string constant” inside the array subscript, but I am confused how it is possible to subscript an integer variable. So I came with this code:

#include <stdio.h>

int main(void) {
    int x = 10;

    printf("%d", x["\0"]); /* What is x["\0"]?! */

    return 0;

}

It compiles without error using MinGW with -Wall -ansi -pedantic. This code then outputs: 105.

Can anyone interpret this?

Edit: I found that there must be a pointer inside the subscript, or else I get compile-time error.

Answer 1

It’s a well-known trick. Because of the way pointer arithmetic works, the following are synonymous:

• v[5]
• 5[v]
• *(v + 5)

It’s the same thing when v happens to be a string literal.