SWIG Users Guide

Pointers, Constraints, and Typemaps

102

void foo1(int *);

// Apply int * typemap

void foo2(int a[4]);

// Apply int[4] typemap

void foo3(int out[4]);

// Apply int out[4] typemap

void foo4(int *status);

// Apply int *status typemap

void foo5(int a[20]);

// Apply int * typemap (because int [20] is an int *)

Common Typemap Methods

%typemap(lang,in)

Convert function arguments from the scripting language to a C

representation.

%typemap(lang,out)

Converts the return value from a function to a scripting lan-

guage representation.

%typemap(lang,ret)

Cleans up the return value of a function. For example, this

could be used to free up memory that might have been allo-

cated by the underlying C function. This code is executed

before a function returns control back to the scripting language.

%typemap(lang,freearg)

Cleans up arguments. This method can be used to clean up

function arguments that might have required memory alloca-

tion or other special processing.

%typemap(lang,argout)

Outputs argument values. This typemap can be used to make a

function return a value from one of its arguments.

%typemap(lang,check)

Checks validity of function inputs. Can be used to apply con-

straints, raise exceptions, or simply for debugging.

%typemap(lang,varin)

Used by some languages to set the value of a C global variable.

Converts a datatype from the scripting language to C. This

method is only used if the “in” method won’t work for some

reason.

%typemap(lang,varout)

Variable. Convert the value of a C global variable to a scripting

language representation.

%typemap(lang,const)

Specifies the code used to create a constant in the module ini-

tialization function. Not supported by all languages.

%typemap(lang,memberin)

Set structure member. Specifies special processing of structure

and class members when setting a value.

%typemap(lang,memberout)

Get structure member. Special processing applied when

retrieving a structure member.

Common Typemap Methods

%typemap(lang,arginit)

Initializes a parameter to an initial value (for example, setting a

pointer to a NULL value). Sometimes useful in determining

whether a parameter was received correctly.

%typemap(lang,default)

Can be used to set a default argument value. Overrides any

other default arguments that might have been specified.

%typemap(lang,ignore)

Set an argument to a default value and ignore it for the pur-

poses of generating wrapper code. (An ignored argument

becomes a hidden argument in the scripting interface).

/* A generic wrapper function */

int wrap_func(int argc, Arg *args[]) {

int arg0;

%typemap(lang,default)

int retval;

%typemap(lang,arginit)

...

%typemap(lang,ignore)

/* Check argument count */

...

/* Parse arguments */

%typemap(lang,in)

arg0 = Get_Int(args[0]);

%typemap(lang,check)

...

/* Call the C function */

retval = func(arg0);

/* Return the result */

%typemap(lang,out)

Set_ResultInt(retval);

%typemap(lang,argout)

/* Clean up or return args */

...

%typemap(lang,freearg)

/* Clean up return result */

%typemap(lang,ret)

...

return OK;

}