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CPPAWK-CASE(1) Case Macro CPPAWK-CASE(1)
NAME
case - macro for portable switch statement
SYNOPSIS
#include <case.h>
case (expr) {
of ("abc")
print "single key abc case"
cbreak
of (1, 2, 3)
print "multi-key 1, 2, 3 case"
cfall # fall through
matching (/regex1/, /regex2/, /regex3/)
print "regex case"
cbreak
mixed (("def", "ghi"), (/regex4/, /regex5/))
otherwise
print "default case"
}
DESCRIPTION
The case macro provides syntax which cppawk translates very directly to the GNU Awk switch
statement, or else to alternative code which works with other Awk implementations.
The purpose of the macro is easy conversion of switch code; therefore, it has the same se-
mantics with regard to fall through between cases, requiring an explicit break.
The clauses of case are labeled with the identifiers of, matching, or mixed, which take
arguments, and are followed by one or more statements. The last one of those statements
must always be a cbreak, cfall or cret statement, described below.
Regular expression keys must use the matching label; ordinary keys compared for equality
must use the of label. The mixed label allows for both keys to be included in one case.
The of and matching macros take variable arguments. Multiple matching keys or regular ex-
pressions are specified as multiple arguments, rather than by repetition of the construct:
of (3) of (4) print "3 or 4"; cbreak // incorrect
of (3, 4) print "3 or 4"; cbreak // correct
The mixed macro takes exactly two arguments, which are parenthesized lists of keys. The
left list must be a list of ordinary value keys, and the second of regular expression lit-
erals:
mixed ((1, 2, "a"), (/xyz$/, /^\t/))
Each clause must specify how it terminates: whether it breaks out of the case statement,
"falls through" to the next case, or returns from the surrounding function. The macros
cbreak, cfall and cret must be used for this purpose. The cret macro takes exactly one ar-
gument, the expression whose value is to be returned from the surrounding function:
function f(input,
case_temps)
{
case (input) {
match (/abc/)
print "match on regex /abc/"
cret(1)
otherwise
cbreak
}
// other logic
return 0
}
When case is transformed into portable code rather than switch, that code depends on hid-
den state variables. If case is used in a top-level BEGIN, END or Awk action, those vari-
ables will be global. They will also be global if case is used in a function, unless de-
fined as local variables in the parameter list.
Defining the temporary variables as local is done using the provided case_temps macro:
#include <case.h>
function fun(x, y, z, # arguments
a, b, # locals
case_temps) # locals for case
{
case (x) {
of (42) {
...
}
...
}
}
case_temps does not have to be in the last argument position. It is guaranteed to expand
to one or more identifiers separated by commas, with no leading or trailing comma. When
the target is GNU Awk, case_temps expands to an unspecified identifier in the __[a-z] re-
served namespace.
SEE ALSO
cppawk(1)
BUGS
The case macro does not currently safely nest with itself.
Forgetting to declare the temporary variables is a programmer pitfall.
AUTHOR
Kaz Kylheku <kaz@kylheku.com>
COPYRIGHT
Copyright 2022, BSD2 License.
cppawk Libraries 19 April 2022 CPPAWK-CASE(1)
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