mirror of
https://github.com/KarolS/millfork.git
synced 2024-10-30 21:30:52 +00:00
41 lines
1.9 KiB
Markdown
41 lines
1.9 KiB
Markdown
[< back to index](../index.md)
|
|
|
|
# Undefined behaviour
|
|
|
|
Since Millfork is only a middle-level programming language and attempts to eschew runtime checks in favour of performance,
|
|
there are many situation when the program may not behave as expected.
|
|
In the following list, "undefined value" means an arbitrary value that cannot be relied upon,
|
|
and "undefined behaviour" means arbitrary and unpredictable behaviour that may lead to anything,
|
|
even up to hardware damage.
|
|
|
|
* array overruns: indexing past the end of an array leads to undefined behaviour
|
|
|
|
* stray pointers: indexing a pointer that doesn't point to a valid object or indexing it past the end of the pointed object leads to undefined behaviour
|
|
|
|
* reading uninitialized variables: will return undefined values
|
|
|
|
* reading variables used by return dispatch statements but not assigned a value: will return undefined values
|
|
|
|
* reading a loop variable after the loop without initializing it again: will return undefined values
|
|
|
|
* returning a value from a function by return dispatch to a function of different return type: will return undefined values
|
|
|
|
* passing an index out of range for a return dispatch statement
|
|
|
|
* stack overflow: exhausting the hardware stack due to excess recursion, excess function calls or excess stack-allocated variables
|
|
|
|
* on ROM-based platforms: writing to arrays
|
|
|
|
* on ROM-based platforms: using global variables with an initial value (they will not be initialized!)
|
|
|
|
* violating the [safe assembly rules](../lang/assembly.md)
|
|
|
|
* violating the [safe reentrancy rules](../lang/reentrancy.md)
|
|
|
|
* when using modifying operators: calling non-pure functions in the left-hand-side index expression (like in `a[f()] += b`).
|
|
Currently, such functions may be evaluated either once or twice. This might be fixed in the future.
|
|
|
|
* when using modifying operators: calling functions on the right-hand-side index expression than modify any of the variables used on the left hand side
|
|
|
|
The above list is not exhaustive.
|