chPeek (Function)

The "chPeek()" function works like the chRead() function except for the fact that the message will not be removed from the channel and will never be blocked.

Input:

ch : CHANNEL

The channel to peek the message from.        

msg : PTR

Pointer to buffer where the message is to be stored.

lenmax : INT

Size of the buffer that msg points to.

If the size of the message in the channel is larger than lenmax, only lenmax bytes will be read.

Returns: INT

Declaration:

FUNCTION chPeek : INT;
VAR_INPUT
  ch     : CHANNEL;
  msg   : PTR;
  lenmax : INT;
END_VAR;

Example:

THREAD_BLOCK Thread;
VAR_INPUT
  ch : CHANNEL;
  id : SINT;
  ...
END_VAR;
VAR
  buf : ARRAY[1..30] OF SINT;
  len : INT;
  ...
END_VAR;
  ...
  // Do while channel initialized
  WHILE chStatus(ch:=ch) > -1 DO
    // peek at data
     len := chPeek(ch:=ch,msg:=ADDR(buf),lenmax:=SIZEOF(buf));
    IF len > 0 THEN
        // Is package sent to me?
        IF buf[1] = id THEN
          // Read data
          chRead(ch:=ch,msg:=ADDR(buf),lenmax:=SIZEOF(buf));
          // Act on data
           ...
        END_IF;
    END_IF;
     ...
  END_WHILE;
END_THREAD_BLOCK;