Macro variables
are tools that enable you to dynamically modify the text in a SAS
program through symbolic substitution. You can assign large or small
amounts of text to macro variables, and after that, you can use that
text by simply referencing the variable that contains it.
Macro variable values have a maximum length
of 65,534 characters. The length of a macro variable is determined
by the text assigned to it instead of a specific length declaration.
So its length varies with each value that it contains. Macro variables
contain only character data. However, the macro facility has features
that enable a variable to be evaluated as a number when it contains
character data that can be interpreted as a number. The value of a
macro variable remains constant until it is specifically changed.
Macro variables are independent of SAS data set variables.
Note: Only printable characters
should be assigned to macro variables. Non-printable values that
are assigned to macro variables can cause unpredictable results.
Macro variables defined by
macro programmers are called
user-defined macro variables. Those defined by the macro processor are called
automatic
macro variables. You can define and use macro variables
anywhere in SAS programs, except within data lines.
When a macro
variable is defined, the macro processor adds it to one of the program's
macro variable symbol tables. When a macro variable is defined in
a statement that is outside a macro definition (called
open code) or when the variable is created automatically
by the macro processor (except SYSPBUFF), the variable is held in
the global symbol table, which the macro processor creates at the
beginning of a SAS session. When a macro variable is defined within
a macro and is not specifically defined as global, the variable is
typically held in the macro's local symbol table, which SAS creates
when the macro starts executing. For more information about symbol
tables, see
SAS Programs and Macro Processing and
Scopes of Macro Variables. When it is in the global symbol table, a macro variable
exists for the remainder of the current SAS session. A variable in
the global symbol table is called a
global macro variable. This variable has global scope because its value is available to
any part of the SAS session (except in CARDS or DATALINES statements).
Other components of SAS might create global macro variables, but only
those components created by the macro processor are considered
automatic macro variables.
When it is in a local
symbol table, a macro variable exists only during execution of the
macro in which it is defined. A variable in a local symbol table is
called a
local macro variable. It has local
scope because its value is available only while the macro is executing.
SAS Programs and Macro Processing contains figures that illustrate
a program with a global and a local symbol table.