How to prevent this happen while trading?

[moonsboy]

I don't want big slippage happen while opening or closing orders. 

However, the slippage is still often much higher as over "10" although I set "slippage=3" already.

Now that the slippage in "OrderSend()" and "OrderClose()" don't work at all, why MQ team added it as the function parameters?

How can I exactly prevent big slippage happen with my code? 

[William Roeder]

They didn't add it when it doesn't work; it was in there before ECNs when it did. Removing it would break existing code.

There is nothing that can be done in your code; only in the broker's server.