Example of Bounds Checking At Compile Time

example.c

typedef union TPM2B_FOO TPM2B_FOO;
union TPM2B_FOO {
    struct {
        uint16_t size;
        uint8_t data[32];
    }t;
    TPM2B b;
};

int main(int argc, char *argv[]) {
    (void) argv;

    TPM2B_FOO foo = {
        // Nested initializers need another level
        .t = {
            .size = 3
        },
    };
    // This will cause error: array index 45 is past the end of the array (which contains 32 elements)
    foo.t.data[45] = argc;
    printf("foo.t.size: %u", foo.t.size);

    // This will bypass compiler checks
    foo.b.data[45] = argc;
    printf("foo.b.size: %u", foo.b.size);
    printf("foo.b.data[45]: %u", foo.b.data[45]);

    return 0;
}

Compile with clang:

clang -Wall -Werror -Wextra -o go a.c

a.c:28:5: error: array index 45 is past the end of the array (which contains 32 elements) [-Werror,-Warray-bounds]