1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
|
[comment {-*- mode: tcl ; fill-column: 90 -*-}]
[list_begin enumerated]
[enum] For all that this is a part of how to
[sectref {Using External Libraries} {Use External Libraries}], for the demonstratation
only the basics are needed.
[enum][vset base][example {
critcl::ccode {
typedef struct vec2 {
double x;
double y;
} vec2;
typedef vec2* vec2ptr;
int
GetVecFromObj (Tcl_Interp* interp, Tcl_Obj* obj, vec2ptr* vec)
{
int len;
if (Tcl_ListObjLength (interp, obj, &len) != TCL_OK) return TCL_ERROR;
if (len != 2) {
Tcl_SetObjResult (interp, Tcl_ObjPrintf ("Expected 2 elements, got %d", len));
return TCL_ERROR;
}
Tcl_Obj* lv[2];
if (Tcl_ListObjGetElements (interp, obj, &lv) != TCL_OK) return TCL_ERROR;
double x, y;
if (Tcl_GetDoubleFromObj (interp, lv[0], &x) != TCL_OK) return TCL_ERROR;
if (Tcl_GetDoubleFromObj (interp, lv[1], &y) != TCL_OK) return TCL_ERROR;
*vec = Tcl_Alloc (sizeof (vec2));
(*vec)->x = x;
(*vec)->y = y;
return TCL_OK;
}
}
critcl::argtype vec2 {
if (GetVecFromObj (interp, @@, &@A) != TCL_OK) return TCL_ERROR;
} vec2ptr vec2ptr
critcl::argtyperelease vec2 {
/* @A : C variable holding the data to release */
Tcl_Free ((char*) @A);
}
critcl::cproc norm {vec2 vector} double {
double norm = hypot (vector->x, vector->y);
return norm;
}
}][vset rebuild]
[enum] The structure to pass as argument is a 2-dimensional vector. It is actually passed
in as a pointer to a [type vec2] structure.
This pointer is created by the [fun GetVecFromObj] function. It allocates and fills the
structure from the Tcl value, which has to be a list of 2 doubles. The bulk of the code in
[fun GetVecFromObj] is for verifying this and extracting the doubles.
[enum] The [cmd argtyperelease] code releases the pointer when the C function returns. In
other words, the pointer to the structure is owned by the translation layer and exists
only while the function is active.
[enum] While working this code has two disadvantages.
First there is memory churn. Each call of [cmd norm] causes the creation and release of a
temporary [type vec2] structure for the argument.
Second is the need to always extract the data from the [type Tcl_Obj*] value.
[para] Both can be done better.
[para] We will come back to this after explaining how to return structures to Tcl.
[list_end]
|
