ZBasic System Library
190
ZBasic Microcontrollers
Type
Function returning String
Invocation
Mid(str, pos, length) or
Mid(str, pos)
Parameter
Method
Type
Description
str
ByVal*
String
The string from which to extract or modify a substring.
pos
ByVal
int8/16
The position of the first character of the substring.
length
ByVal
int8/16
The length of the substring to extract or modify.
* When used on the left hand side of an assignment, this parameter is passed ByRef.
Discussion
This function can be used to extract a portion of a string or to modify a portion of a string, depending on
how it is used. When it appears in the context of a function call, it returns a new string extracted from the
string provided. The first character of the extracted substring will be the character at the position given by
pos (where the first character of the string is position 1). The length of the returned string will be the
number of characters in the source string beginning at the starting index through the end of the string or
the specified length (if present), whichever is less. If the starting position is beyond the end of the string
or if the specified length is less than or equal to zero, the returned string will be of zero length.
When used on the left hand side of an assignment operator, the Mid() function replaces a sequence of
characters in a string with characters from the string value on the right hand side of the assignment
operator.
Dim s as String
s = "abcdef"
Mid(str, 3) = "##"
' result is "ab##ef"
Note that when used in this way the first parameter is passed by reference so it cannot be a literal string
or any other entity than cannot be passed by reference. Also, the length of the target string will never be
changed. The number of characters overwritten in the destination string will be the lesser of a) the
number of characters in the string on the right hand side of the assignment, b) the number of characters
specified in the third parameter (if present), and c) the number of characters in the target string beginning
at the position specified by the second parameter through the end of the string.
Compatibility
In BasicX, the first parameter is pass-by-reference. This disallows any use of a string literal for the first
parameter. Also, in BasicX the third parameter must always be provided.
The BasicX documentation suggests that using Mid() on the left hand side of an assignment might result
in a change in the string length. Tests indicate that this is not the case. Moreover, execution of the code
fragment below actually results in a garbage character being placed in the third character position.
Dim s as String
s = "abc"
Mid(s, 2, 2) = "!"
' result is "a!@" (@ is an indeterminate character)
See Also
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