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The following routines provide the ability to access and update
global awk
-level variables by name. In compiler terminology,
identifiers of different kinds are termed symbols, thus the “sym”
in the routines’ names. The data structure that stores information
about symbols is termed a symbol table.
The functions are as follows:
awk_bool_t sym_lookup(const char *name,
awk_valtype_t wanted,
awk_value_t *result);
Fill in the awk_value_t
structure pointed to by result
with the value of the variable named by the string name
, which is
a regular C string. wanted
indicates the type of value expected.
Return true if the actual type matches wanted
, and false otherwise.
In the latter case, result->val_type
indicates the actual type
(see Table 17.2).
awk_bool_t sym_lookup_ns(const char *name,
const char *name_space,
awk_valtype_t wanted,
awk_value_t *result);
This is like sym_lookup()
, but the name_space
parameter allows you
to specify which namespace name
is part of. name_space
cannot be
NULL
. If it is ""
or "awk"
, then name
is searched
for in the default awk
namespace.
Note that namespace
is a C++ keyword. For interoperability with C++,
you should avoid using that identifier in C code.
awk_bool_t sym_update(const char *name, awk_value_t *value);
Update the variable named by the string name
, which is a regular
C string. The variable is added to gawk
’s symbol table
if it is not there. Return true if everything worked, and false otherwise.
Changing types (scalar to array or vice versa) of an existing variable
is not allowed, nor may this routine be used to update an array.
This routine cannot be used to update any of the predefined
variables (such as ARGC
or NF
).
awk_bool_t sym_update_ns(const char *name_space, const char *name, awk_value_t *value);
This is like sym_update()
, but the name_space
parameter allows you
to specify which namespace name
is part of. name_space
cannot be
NULL
. If it is ""
or "awk
, then name
is searched
for in the default awk
namespace.
An extension can look up the value of gawk
’s special variables.
However, with the exception of the PROCINFO
array, an extension
cannot change any of those variables.
When searching for or updating variables outside the awk
namespace
(see section Namespaces in gawk
), function and variable names must be simple
identifiers.107 In addition, namespace names and variable and function names
must follow the rules given in Namespace and Component Naming Rules.
Allowing both namespace plus identifier and
foo::bar
would have been too confusing to document, and to code
and test.
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