a_VAR
typedef struct {
  double dval;          /* the variable's numeric value */
  char * ptr;           /* pointer to string, array or RE structure */
  unsigned int slen;    /* length of string ptr as per strlen */
  unsigned int allc;    /* space mallocated for string ptr */
  char type;            /* records current cast of variable */
  char type2;           /* double-typed variable flag, explained later. */
  char temp;            /* TRUE if a temporary variable */
} a_VAR;
The a_VAR structure is used to store everything related to AWK
variables.  This includes those named & used in your program, and 
transient variables created to return values from functions and other
operations like string concatenation.  As such, this structure is
ubiquitous throughout libawka and awka-generated code.
The type value is set to one of a number of #define values, 
described in the Defines paragraph below.  Many functions and macros 
exist for working with the contents of a_VARs - see the Functions & 
Macros paragraph for details.

a_VARARG
typedef struct {
  a_VAR *var[256];
  int used;
} a_VARARG;
This structure is typically used to pass variable numbers of a_VARs to 
functions.  Up to 256 a_VARs may be referenced by an a_VARARG, and the
used value contains the number of a_VARs present.

struct gvar_struct
struct gvar_struct {
  char *name;
  a_VAR *var;
};
Provides a mapping of the global variable names in an AWK script to pointers
to their a_VAR structures.

a_VAR * a_bivar[a_BIVARS]
This array contains all the AWK internal variables, such as ARGV, ARGV, 
CONVFMT, ENVIRON and so on, along with $0 and the field variables $1..$n.  
a_BIVARS is a define, as are the identities of which element in the 
array belongs to which variable.  Again, look for functions that manage 
these variables rather than working with them directly if possible.

extern struct gvar_struct *_gvar;
This is actually created & populated by the translated C code generated 
by awka, rather than by libawka.a.  It is a NULL-terminated array 
of the gvar_struct structure defined earlier in this page, and contains 
the names of all global variables in an AWK script, mapped to their a_VAR 
structures.

a_VARNUL - the type value of an a_VAR if the variable is unused.

a_VARDBL - the type value for an a_VAR cast to a number.

a_VARSTR - type where the a_VAR has been cast to a string.

a_VARARR - type where the a_VAR contains an array.

a_VARREG - type where the a_VAR contains a regular expression.

a_VARUNK - type where the a_VAR is a string, but could also be a
         number.  Variables populated by getline, the FILENAME variable,
         and elements of an array created by split(), are all of this
         special type.

a_DBLSET - for a string a_VAR that has been read in context as a number, the
         type2 flag is set to this #define to prevent the string-to-number
         conversion being done again.

a_STRSET - the opposite of the above.  The variable is a number, has been read
         as a string, hence the value of ptr is current, and the type2
         flag is set to this #define.

a_BIVARS provides the number of elements in the a_bivar[] array.

awka_getd(a_VAR *)
This macro calls the awka_getdval() function, appending the calling file & line number 
for debug purposes.  It read-casts the variable to a number, and returns the double
value of the variable.  By read-cast, we mean that if the variable is a string it
remains so, but dval is set, and type2 is set to a_DBLSET.  But if the a_VAR
is a regular expression, the re structure is dropped and the variable converted to a
number.  If you're not sure whether an a_VAR you're about to read is a number, and you
want to read it as one, simply call awka_getd(varname) - its the easiest way.

awka_getd1(a_VAR *)
Same as awka_getd, except this will be faster if the a_VAR * is a variable.  Do not
use this if the a_VAR * is a function call return value, as it'll call the function
several times!  In this case, use awka_getd() instead.

awka_gets(a_VAR *)
Similar to awka_getd(), this read-casts an a_VAR to a string, and returns the character
array pointed to by ptr.

awka_gets1(a_VAR *)
Use this where the a_VAR * is a variable, not a function call that returns an a_VAR *,
for faster performance.

awka_getre(a_VAR *)
Write-casts the a_VAR * to a regular expression, and returns the pointer to the awka_regexp
structure.  Write-cast means that the existing contents of the variable are dropped in
favour of the new contents.

static char *awka_strcpy(a_VAR *var, char *str)
This function sets var to string type, and copies to it the contents of str.
It returns a pointer to var->ptr.

a_VAR *awka_varcpy(a_VAR *va, a_VAR *vb)
This function copies the contents of scalar a_VAR *vb to scalar a_VAR *va, 
and returns a pointer to va.

double awka_varcmp(a_VAR *va, a_VAR *vb)
This function compares the contents of the two scalar variables, and returns 0 if the 
variables are equal, -1 if va is less than vb, or 1 if va is greater.  Numerical 
comparison is used where possible, otherwise string.

a_VAR *awka_vardup(a_VAR *va)
This function creates a new a_VAR *, copies the contents of va, and returns a pointer
to the new structure.

awka_varinit(a_VAR *)
A macro that takes a NULL a_VAR *, mallocs space for it, and initialises it to a_VARNUL.

void awka_killvar(a_VAR *)
Frees all memory used by the a_VAR, except the structure itself.

static a_VAR * awka_argv()
You can use a_bivar[a_ARGV] directly when reading the value of elements in the array,
but when you want to write to the array, use the above function instead, as it will
make sure the changes are recognised elsewhere in libawka.

static a_VAR * awka_argc()
You can use a_bivar[a_ARGC] directly when reading its value, but when you want to write 
to it, use the above function instead, as it will make sure the change is recognised 
elsewhere in libawka.

a_ARR_TYPE_NULL
The 'type' of an array that has not been initialised, or has been deleted.

a_ARR_TYPE_SPLIT
The 'type' of an array populated by the split() builtin function.

a_ARR_TYPE_HSH
The 'type' of arrays populated within the AWK script, eg. arr["pigs"] = cows.

a_ARR_CREATE
When searching arrays, specifies that an element is to be created if it doesn't
already exist in the array.

a_ARR_QUERY
When searching arrays, this will not create a new element if it doesn't already
exist.

a_ARR_DELETE
In an array search, this flag will cause the element to be deleted from the array.

void awka_arraycreate( a_VAR *var, char type );
Allocates an array structure of type type, makes var->ptr point
to it, and sets var->type to a_VARARR.  The type argument may
be one of a_ARR_TYPE_NULL, a_ARR_TYPE_SPLIT or a_ARR_TYPE_HSH, according to
how the array will be populated.

void awka_arrayclear( a_VAR *var );
Assumes var is an a_VARARR, this deletes the contents of the array structure
pointed to by var->ptr.

a_VAR * awka_arraysearch1( a_VAR *v, a_VAR *element, char create, int set );
Searches array variable v for index element.  If it does not exist, and
create is a_ARR_CREATE, a new element in the array for this value will be added.
If the element is found (or created) and create is not a_ARR_DELETE, the
function will return a pointer to the a_VAR for that element.  For a_ARR_DELETE, the
element will be deleted from the array.  The set value should be FALSE.

a_VAR * awka_arraysearch( a_VAR *v, a_VARARG *va, char create );
Searches array variable v as per awka_arraysearch1(), except that this works
with multiple index subscripts (eg, arr[x, y]).

double awka_arraysplitstr( char *str, a_VAR *v, a_VAR *fs, int max );
The AWK builtin split() function.  It splits str into array variable v,
based on fs, up to max number of fields.  If fs is NULL, then
a_bivar[a_FS] will be used.  Otherwise fs may contain an empty string, a
single-character string, or a regular expression.  The number of fields created
in v is returned.

int awka_arrayloop( a_ListHdr *ah, a_VAR *v );
This function implements the "for (i in j)" feature in AWK.  You provide ah, 
making sure it is initialised to zeroes. 
The best way to understand how to call this function is to type:
  awka 'BEGIN { for (i in j) x = j[i]; }'
and see what is generated as a result.  You don't have to understand the a_ListHdr
structure or sub-structures to use this function.

int awka_arraynext( a_VAR *v, a_ListHdr *ah, int pos );
Given that ah has been populated by a call to awka_arrayloop(), this function
copies the (string or integer) element at position pos in the list to v, 
then returns pos+1, or zero if there are no more elements in the array list.

void awka_alistfree( a_ListHdr *ah );
Frees the last list element in ah.

void awka_alistfreeall( a_ListHdr *ah );
Frees all memory held by ah, and sets its contents to zero/NULL.

a_VAR * awka_dol0(int set);
The best means of accessing the $0 a_VAR, as it updates its contents with any pending
changes.  Make set zero if you're reading the value of $0, but if you want to
set $0, make it 1.

a_VAR * awka_doln(int fld, int set);
This function returns the a_VAR * of the $1..$n variable identified by fld, 
updating the field array with any refreshed $0 contents first if necessary.  If you
want to read the value of $fld, make set zero, otherwise it should be 1.

a_VARARG * awka_arg0(char);

a_VARARG * awka_arg1(char, a_VAR *);

a_VARARG * awka_arg2(char, a_VAR *, a_VAR *);

a_VARARG * awka_arg3(char, a_VAR *, a_VAR *, a_VAR *);

a_VARARG * awka_vararg(char, a_VAR *var, ...);
These functions populate & return a pointer to an a_VARARG structure.  The char 
argument, if TRUE, will make you responsible for freeing the structure, otherwise
it'll be a temporary one that libawka will manage.  awka_arg0() will return an
empty structure (ie. no args), awka_arg1() will have one a_VAR * in it, and so
on.  Where you want to put more than four a_VAR *'s inside an a_VARARG, you can 
call awka_vararg with as many as you like, or if there's seriously a lot, maybe
write your own loop of code to populate an a_VARARG - its not rocket science.

_a_IOSTREAM
typedef struct {
  char *name;       /* name of output file or device */
  FILE *fp;         /* file pointer */
  char *buf;        /* input buffer */
  char *current;    /* where up to in buffer */
  char *end;        /* end of data in buffer */
  int alloc;        /* size of input buffer */
  char io;          /* input or output stream flag */
  char pipe;        /* true/false */
  char interactive; /* whether from a /dev/xxx stream or not */
} _a_IOSTREAM;
extern _a_IOSTREAM *_a_iostream;
extern int _a_ioallc, _a_ioused;
Controls input and output streams used by AWK's getline, print and printf
builtin functions.  The two int variables record the space allocated in the 
_a_iostream array, and the number of elements used, respectively.  I list this 
information here in case you wish to create fread, fwrite and fseek functions for 
awka, as these will need low-level access to the streams.

a_VAR * awka_getline(char keep, a_VAR *target, char *input, int pipe, char main);
As previously described, keep controls whether you want to be responsible for
freeing the a_VAR the function returns or not.  Moving on, target is the a_VAR
to hold the line of data to be read (you provide this one).  input is the name
of the input file or command.  pipe is TRUE if input is a command rather
than a file, eg. "sort stuff | getline x".  main should always be false.
If input is NULL, getline will try to read from the file identified by 
a_bivar[a_FILENAME], or from the next element in the a_bivar[a_ARGV] array.

awka_getre(a_VAR *)
This macro is the easiest method of creating & compiling a regexp.  Providing you've
set the a_VAR to the string value of the re pattern, this macro call works a treat.

a_VAR *awka_match(char keep, char fcall, a_VAR *va, a_VAR *rva);
This function is the implementation of AWK's match() function, and is the most
simple way of evaluating an RE against a string.  keep is as previously
discussed, fcall should be set to TRUE if you want a_bivar[a_RSTART] and
a_bivar[a_RLENGTH] to be set, otherwise FALSE, va contains the string, and
rva contains the regular expression.  The numerical a_VAR returned is
1 on success, zero on failure.