This lesson's interactive features are locked, please to keep using them

Memory Layout

Unions store their value in the same memory location, no matter which field or type is actively being used. That means that accessing any field apart from the one you set is generally a bad idea.

Assignment

Take a look at the val_or_err_t union. It represents either an integer value or an unsigned (non-negative) integer error code.

Run the code in its current state.

Notice that the .value field is set to -420, then the data in each field is printed. The .value field works as you'd expect, printing -420. However, the .err field prints 4294966876! It's trying to interpret the bytes of -420 as an unsigned integer, which results in a very large number.
Uncomment the next block of code, and run it without submitting.

Notice that now we set the .err field (an unsigned integer) to UINT_MAX, which is a constant representing the largest possible unsigned integer (4294967295 in my case). As expected, the .err field prints 4294967295. However, the .value field prints -1! It's reading the bytes for 4294967295 as a signed integer instead of an unsigned one, which turns it into -1.

Submit the fully uncommented code.