__LINE__ returns the line of code its on, and % 10 means “remainder 10.” Examples:
1 % 10 == 1 ... 8 % 10 == 8 9 % 10 == 9 10 % 10 == 0 <-- loops back to 0 11 % 10 == 1 12 % 10 == 2 ... 19 % 10 == 9 20 % 10 == 0 21 % 10 == 1
In code, 0 means false and 1 (and 2, 3, 4, …) means true.
So, if on line 10, you say:
int dont_delete_database = true;
then it will expand to:
int dont_delete_database = ( 10 % 10 ); // 10 % 10 == 0 which means false // database dies...
if you add a line before it, so that the code moves to line 11, then suddenly it works:
// THIS COMMENT PREVENTS DATABASE FROM DYING int dont_delete_database = ( 11 % 10 ); // 11 % 10 == 1, which means true
yggdar@lemmy.world 4 months ago
That exact version will end up making “true” false any time it appears on a line number that is divisible by 10.
During the compilation, “true” would be replaced by that statement and within the statement, “LINE” would be replaced by the line number of the current line. So at runtime, you end up witb the line number modulo 10 (%10). In C, something is true if its value is not 0. So for e.g., lines 4, 17, 116, 39, it ends up being true. For line numbers that can be divided by 10, the result is zero, and thus false.
In reality the compiler would optimise that modulo operation away and pre-calculate the result during compilation.
The original version constantly behaves differently at runtime, this version would always give the same result… Unless you change any line and recompile.
One downside compared to the original version is that the value of “true” can be 10 different things (anything between 0 and 9), so you would get a lot more weird behaviour since “1 == true” would not always be true.
A slightly more consistent version would be
((__LINE__ % 10) > 0)BananaOnionJuice@lemmy.dbzer0.com 4 months ago
If the error is too frequent it will be hunted down very fast, what you want is errors that happen no more than once every month, maybe add another level that ensures this only triggers based on the running time.
BaumGeist@lemmy.ml 4 months ago
It actually doesn’t, since rand() is deterministic.
When no seed value is specified, rand() is automatically seeded with 1 at the initial call within any program It then uses the previous output as seed for the next, so it will always have the same output sequence
yggdar@lemmy.world 4 months ago
That is true, but from a human perspective it can still seem non-deterministic! The behaviour of the program as a whole will be deterministic, if all inputs are always the same, in the same order, and without multithreading. On the other hand, a specific function call that is executed multiple times with the same input may occasionally give a different result.
Most programs also have input that changes between executions. Hence you may get the same input record, but at a different place in the execution. Thus you can get a different result for the same record as well.