MID block
Short summary
Name |
MID |
→POU type |
|
Category |
|
Conform to →IEC-standard |
currently restricted
|
Graphical interface |
|
Available since |
version 1.32.0 (for logi.CAD 3) |
Functionality
The block returns a partial string of another string.
At input IN, enter a string. At input L, enter the number of characters to return (= the length of the part to return). At input P, enter the start position in the string.
Special cases (see under "Example for usage within ST-editor" ) :
In case of L = 0, the block returns an empty string ''. In this case, the output ENO is set to value TRUE.
If a negative value is connected to L, the corresponding characters before the position P are deleted in the string. In this case, the output ENO is set to value FALSE. If the block would access characters outside of the visible range (in front of position 1), the block returns an empty string ''.
If the value 0 or a negative value is connected to P, the block does not return any characters. In this case, the output ENO is set to value FALSE as well.
If the value for L and/or P is > the length of the string value for IN , the block does not return any characters or just the characters that are within the visible range . In this case, the output ENO is set to value FALSE .
logi.CAD 3 determines the character positions within a string as follows: 1, 2, ..., n. 1 corresponds to the leftmost character position and n to the length of the string.
Three-character combination of the dollar sign ($) followed by two hexadecimal digits are evaluated as single character. Example: The string '$B15' (corresponds to '±5') consists of 2 characters. See →character string literal for more examples for those combinations.
Inputs, return value
|
Identifier |
Description |
|
Inputs: |
IN |
STRING |
input value |
L |
USINT, UINT, UDINT, ULINT, SINT, INT, DINT or LINT(corresponds to →generic data type ANY_INT) |
number of characters to return |
|
P |
USINT, UINT, UDINT, ULINT, SINT, INT, DINT or LINT(corresponds to →generic data type ANY_INT) |
start position within input value |
|
Return value: |
– |
STRING |
|
Input EN and output ENO are available when →calling the block. See "Execution control: EN, ENO" for information on input EN and output ENO.
See:
"Blocks for safe logic" whether this block is supported for developing safety-relevant applications.
"Highlighting safe logic in the FBD-editor" for the effects when using the block as a block for safe logic .
Internal error diagnostic for block
The block checks the would-be return value.
If the return value cannot be mapped in the available memory (the return value is too large), the output ENO of the block is set to value FALSE (or an equivalent). When you are using nested blocks with STRING values, observe that the memory for STRING values is restricted (see "In case of nested string blocks: How can the return value be entirely mapped ?" for details and examples).
Moreover, the block checks the connected values whether a non-existent character position in a string is accessed. This is the case, if the value for L or P is > the length of the string value for IN, a negative value is connected to L or P or value 0 is connected to P. The output ENO of the block is set to value FALSE (or an equivalent) in both these cases.
Example for usage within ST-editor
PROGRAM Test
VAR
result1, result3, result4, result5, result6, result7, result8 : STRING[
8
];
result2 : STRING[
2
];
CheckENO1, CheckENO2, CheckENO3, CheckENO4, CheckENO5, CheckENO6, CheckENO7, CheckENO8 : BOOL;
END_VAR
result1 := MID(IN :=
'astring'
, L :=
3
, P :=
4
, ENO => CheckENO1);
(* The variable
'result1'
evaluates to <
'rin'
>. The variable
'CheckENO1'
evaluates to
'TRUE'
. *)
result2 := MID(IN :=
'astring'
, L :=
3
, P :=
4
, ENO => CheckENO2);
(* The variable
'result2'
evaluates to <
'ri'
>. The variable
'CheckENO2'
evaluates to
'FALSE'
. Reason:
'result2'
is declared with length
'2'
and the would-be
return
value exceeds
this
length. *)
result3 := MID(IN :=
'astring'
, L :=
0
, P :=
4
, ENO => CheckENO3);
(* The variable
'result3'
evaluates to <
''
>, i.e an empty string. The variable
'CheckENO3'
evaluates to
'TRUE'
. Reason: value
'0'
for
'L'
*)
result4 := MID(IN :=
'astring'
, L := -
2
, P :=
4
, ENO => CheckENO4);
(* The variable
'result4'
evaluates to <
'st'
>. The variable
'CheckENO4'
evaluates to
'FALSE'
. Reason: negative value
for
'L'
*)
result5 := MID(IN :=
'astring'
, L := -
2
, P :=
1
, ENO => CheckENO5);
(* The variable
'result5'
evaluates to <
''
>, i.e an empty string. The variable
'CheckENO5'
evaluates to
'FALSE'
. Reason: negative value
for
'L'
*)
(* None of the characters are returned because characters outside the visible range would be accessed. *)
result6 := MID(IN :=
'astring'
, L :=
3
, P := -
1
, ENO => CheckENO6);
(* The variable
'result6'
evaluates to <
''
>, i.e an empty string. The variable
'CheckENO6'
evaluates to
'FALSE'
. Reason: negative value
for
'L'
*)
result7 := MID(IN :=
'astring'
, L :=
13
, P :=
2
, ENO => CheckENO7);
(* The variable
'result7'
evaluates to <
'string'
>, i.e an empty string. The variable
'CheckENO7'
evaluates to
'FALSE'
. Reason: value
for
'L'
> the length of string
'astring'
*)
result8 := MID(IN :=
'deviation: $B15'
, L :=
2
, P :=
12
, ENO => CheckENO8);
(* The variable
'result8'
evaluates to <
'$B15'
>, i.e an empty string. The variable
'CheckENO8'
evaluates to
'TRUE'
. *)
END_PROGRAM
When creating your application within the ST-editor, enter a call of a block by typing the text as requested by the syntax or use Content Assist.