A string is a set of characters: letters, digits, punctuation, and so on delimited by a matched set of quotation marks ("):
SET string = "This is a string"
Topics about strings include:
InterSystems IRIS Data Platform™ supports a maximum string length of 3,641,144 characters. Attempting to exceed this maximum string length results in a <MAXSTRING> error.
When a process uses a string, the memory for the string comes from the operating system’s malloc() buffer, not from the partition memory space for the process. Thus the memory allocated for actual string values is not subject to the limit set by the maximum memory per process (Maximum per Process Memory (KB)
) parameter and does not affect the $STORAGE
value for the process.
You can include a " (double quote) character as a literal within a string by preceding it with another double quote character:
SET string = "This string has ""quotes"" in it."
There are no other escape character sequences within ObjectScript string literals.
Note that literal quotation marks are specified using other escape sequences in other InterSystems software. Refer to the $ZCONVERT
function for a table of these escape sequences.
SET a = "Inter"
SET b = "Systems"
SET string = a_b
By using the concatenate operator you can include non-printing characters in a string. The following string includes the linefeed ($CHAR(10)) character:
SET lf = $CHAR(10)
SET string = "This"_lf_"is"_lf_"a string"
How non-printing characters display is determined by the display device. For example, Terminal differs from browser display of the linefeed character, and other positioning characters. In addition, different browsers display the positioning characters $CHAR(11) and $CHAR(12) differently.
InterSystems IRIS encoded strings — bit strings, List structure strings, and JSON strings — have limitations on their use of the concatenate operator. For further details, see Concatenate Encoded Strings
Some additional considerations apply when concatenating numbers. For further details, see “Concatenating Numbers
You can use the equals (=) and does not equal ('=) operators to compare two strings. String equality comparisons are case-sensitive. Exercise caution when using these operators to compare a string to a number, because this comparison is a string comparison, not a numeric comparison. Therefore only a string containing a number in canonical form
is equal to its corresponding number. ("-0" is not a canonical number.) This is shown in the following example:
WRITE "Fred" = "Fred",! // TRUE
WRITE "Fred" = "FRED",! // FALSE
WRITE "-7" = -007.0,! // TRUE
WRITE "-007.0" = -7,! // FALSE
WRITE "0" = -0,! // TRUE
WRITE "-0" = 0,! // FALSE
WRITE "-0" = -0,! // FALSE
The <, >, <=, or >= operators cannot be used to perform a string comparison. These operators treat strings as numbers
and always perform a numeric comparison. Any non-numeric string is assigned a numeric value of 0 when compared using these operators.
Lettercase and String Comparisons
String equality comparisons are case-sensitive. You can use the $ZCONVERT
function to convert the letters in the strings to be compared to all uppercase letters or all lowercase letters. Non-letter characters are unchanged.
A few letters only have a lowercase letter form. For example, the German eszett ($CHAR(223)) is only defined as a lowercase letter. Converting it to an uppercase letter results in the same lowercase letter. For this reason, when converting alphanumeric strings to a single letter case it is always preferable to convert to lowercase.
A bit string represents a logical set of numbered bits with boolean values. Bits in a string are numbered starting with bit number 1. Any numbered bit that has not been explicitly set to boolean value 1 evaluates as 0. Therefore, referencing any numbered bit beyond those explicitly set returns a bit value of 0.
A bit string has a logical length, which is the highest bit position explicitly set to either 0 or 1. This logical length is only accessible using the $BITCOUNT
function, and usually should not be used in application logic. To the bit string functions, an undefined global or local variable is equivalent to a bitstring with any specified numbered bit returning a bit value 0, and a $BITCOUNT
value of 0.
A bit string is stored as a normal ObjectScript string with an internal format. This internal string representation is not accessible with the bit string functions. Because of this internal format, the string length
of a bit string is not meaningful in determining anything about the number of bits in the string.
Because of the bit string internal format, you cannot use the concatenate operator
with bit strings. Attempting to do so results in an <INVALID BIT STRING> error.
Two bit strings in the same state (with the same boolean values) may have different internal string representations, and therefore string representations should not be inspected or compared in application logic. To the bit string functions, the null strings and undefined global/local variables are equivalent to a bitstring with all bits 0, and a length of 0.
A bit set in a global variable during a transaction
will be reverted to its previous value following transaction rollback
. However, rollback does not return the global variable bit string to its previous string length or previous internal string representation. Local variables are not reverted by a rollback operation.
A logical bitmap structure can be represented by an array of bit strings, where each element of the array represents a "chunk" with a fixed number of bits. Since undefined is equivalent to a chunk with all 0 bits, the array can be sparse, where array elements representing a chunk of all 0 bits need not exist at all. For this reason, and due to the rollback behavior above, application logic should avoid depending on the length of a bit string or the count of 0-valued bits accessible using $BITCOUNT(str) or $BITCOUNT(str,0).
Content Date/Time: 2019-09-19 06:44:29