ii.19.4-filter-blocks.md

II.19.4 Filter blocks

A filter block is declared using the filter keyword.

SEHClause ::= …
| filter Label HandlerBlock
| filter Scope HandlerBlock

The filter code begins at the specified label and ends at the first instruction of the handler block. (Note that the CLI demands that the filter block shall immediately precede, within the CIL stream, its corresponding handler block.)

[Example:

.method public static void m () {
  .try {
    …              // protected instructions
    leave exitSEH  // normal exit
  }
  filter {
    …              // decide whether to handle
    pop            // pop exception object
    ldc.i4.1       // EXCEPTION_EXECUTE_HANDLER
    endfilter      // return answer to CLI
  }
  {
    …              // handle the exception
    pop            // pop the exception object
    leave exitSEH  // leave filter handler
  }
exitSEH:
  …
}

end example]