Does putting a piece in the way stop a cannon?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws and is regression-tested against the official 110-diagram repetition casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it against the engine before publishing.
Direct answer
It depends entirely on what was already there. Adding a piece to an empty line gives the cannon the screen it lacked and switches its attack on. Adding one to a line that already has a screen makes the count two and switches the attack off. Count before you interpose.
The mistake this causes
A chess player's reflex is to block a line to stop an attack. Against a cannon on an empty line, that reflex creates the attack — you have just handed it the screen it was missing, and your blocking piece is now the thing being fired across.
It is the single most expensive habit a chess player brings to xiangqi.
Using it deliberately
Both directions are tactics. Dropping any piece onto an empty line between your cannon and the enemy general creates a check from nothing; moving a piece off a line switches an enemy cannon off. Neither has a chess equivalent, and both are everyday moves here.
Related questions
So how do I block a cannon's check?
By making the screen count wrong — either add a second piece to the line, or remove the existing screen.
Does it matter whose piece the screen is?
No. Only the number of pieces on the line matters.
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