# Substrings

A substring is a set of characters that makes up part of
a whole string. The syntax to specify a substring is:

```
substring= string[m, n]
```
where *string* is a string variable, *m* is the starting character position, and *n* is the substring length. For example, if the current value of variable `S` is the string `"ABCDEFG"`, then the current
value of `S[3,2]` is the substring `"CD"` (the two-character substring starting at character position 3 of
string `S`).

If the starting character specification
is past the end of the string value, then an empty substring value
is selected. If the starting character specification is negative or
zero, then the substring is assumed to start at character one.

If the substring length specification exceeds the remaining number
of characters in the string, then the remaining string is selected.
If the substring length specification is negative or zero, then an
empty substring is selected.

Note: **For Windows:** The maximum
size for a string variable in FlashBASIC is 134 MB.

A segment
of a character string can be changed or substituted without affecting
the remainder of the string by assigning the new segment to the variable
containing the original string. The new segment is assigned to the
original string variable with the starting character and segment length
specified with the variable. The string variable can be a single variable
or an array element. For example, if the current value of the variable `S` above (`"ABCDEFG"`) is to have characters
3 to 5 inclusive replaced by the string `"123"`, the
assignment `S[3,3]="123"` accomplishes this substitution
so that the variable `S` now becomes `"AB123FG"`. The general syntax for substring replacement is:

```
string[m, n] = substring
```
where *string* is a string variable, *substring* is the substring to be inserted, *m* is the starting character position, and *n* is
the number of characters in the string that are replaced.

One
or more fields or substrings within a character string variable that
are delimited by a specific character can be changed by a single assignment.

```
string[delimiter, m, n] = substrings
```
where *string* is a string expression
or variable, *substrings* is one or more substrings
(separated by a delimiter) to be substituted, *delimiter* is the delimiter separating fields or substrings in the original
string, *m* is the starting field position within
the string for the substring to be placed, and *n* is the number of fields or substrings to be replaced.

If *m* is less than 1, 1 is assumed. If *m* is greater than the number of fields within *string* then the number of fields in *string* is increased
by adding null fields separated by the *delimiter* so that *string* has the length of *m* fields. Multiple *substrings* separated by the
specified delimiter can be substituted in the original *string*.

The expression *n* has different effects
depending on whether it is positive, negative or zero. If it is positive,
then *n* fields in *string* are
replaced with *n* substrings. If *m* + *n* is greater than the number of fields
in *string*, then the number of fields in the resulting
string is increased to the value *m* + *n*, and the extra substrings are
concatenated to the end of the original string. If *m* + *n* is less than the number of fields in *string*, but *n* is greater than the
number of *substrings* specified, only the specified
substrings are substituted and the remainder of the *n* fields in string are nulled.

If *n* is zero,
then no fields in *string* are deleted and the specified
substrings are inserted into *string* before the *m*th field. If *n* is less than zero,
then *n* fields greater than or equal to *m* are deleted from *string* and the
entire expression containing the substrings is inserted at that point
in the string.

---
Source: https://d3codex.com/pickbasic-flashbasic/substrings/ - part of the D3Codex reference.