| Re: problem with call_external() [message #5109] |
Mon, 09 October 1995 00:00 |
steinhh
Messages: 260
Registered: June 1994
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Senior Member |
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In article <4527dn$a8r@apakabar.cc.columbia.edu>, chs11@aloha.cc.columbia.edu (Carl H Sayres) writes:
|>
|> In article <450kgr$2tq@hermod.uio.no>,
|> Stein Vidar Hagfors Haugan <steinhh@amon.uio.no> wrote:
|> >In article <44va4a$khr@apakabar.cc.columbia.edu>, chs11@inibara.cc.columbia.edu (Carl H Sayres) writes:
|> >|> I'm trying to pass a two dimensional array of floats to an ansi C function.
|> >|> a = (float **) argv[0]; /* this doesn't work */
|> >
|> >A two-dimensional array is still just an array -- no extra level of
|> >indirection is implied. You're treating a as if it was passed to your
|> >routine in the form of an array of pointers to each row (or column).
|> >This is not the case. Only one pointer is passed, and element a(i,j)
|> >can be found in your C program by the expression *(a + i + j*n).
|>
|> I'm passing the 2-d array to another function which is expecting a
|> float **. Can I create a *float[], and fill in the values ?
|> eg. for an m by n matrix:
|> float ** list;
|> list = (float **) malloc(sizeof(float *) * m);
|> for(i=0;i<m;i++) list[i] = (a + i*m);
|>
|> will that work?
|>
If I understand your description correctly, the answer is yes.
The way I understand it is that your function expects a pointer
to a table of pointers to floats. Each pointer in the table points
to one row or column in the two-dimensional array.
It could be, however, that your function expects a pointer
to *just one* pointer that points to the whole, contiguous table
of values. In that case, use (float **) &argv[0] as the
argument to the function.
Stein Vidar
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| Re: problem with call_external() [message #5123 is a reply to message #5109] |
Fri, 06 October 1995 00:00  |
chs11
Messages: 14
Registered: October 1995
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Junior Member |
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In article <450kgr$2tq@hermod.uio.no>,
Stein Vidar Hagfors Haugan <steinhh@amon.uio.no> wrote:
> In article <44va4a$khr@apakabar.cc.columbia.edu>, chs11@inibara.cc.columbia.edu (Carl H Sayres) writes:
> |> I'm trying to pass a two dimensional array of floats to an ansi C function.
> |> a = (float **) argv[0]; /* this doesn't work */
>
> A two-dimensional array is still just an array -- no extra level of
> indirection is implied. You're treating a as if it was passed to your
> routine in the form of an array of pointers to each row (or column).
> This is not the case. Only one pointer is passed, and element a(i,j)
> can be found in your C program by the expression *(a + i + j*n).
I'm passing the 2-d array to another function which is expecting a
float **. Can I create a *float[], and fill in the values ?
eg. for an m by n matrix:
float ** list;
list = (float **) malloc(sizeof(float *) * m);
for(i=0;i<m;i++) list[i] = (a + i*m);
will that work?
Carl
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| Re: problem with call_external() [message #5127 is a reply to message #5123] |
Thu, 05 October 1995 00:00 |
steinhh
Messages: 260
Registered: June 1994
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Senior Member |
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In article <44va4a$khr@apakabar.cc.columbia.edu>, chs11@inibara.cc.columbia.edu (Carl H Sayres) writes:
|> I'm trying to pass a two dimensional array of floats to an ansi C function.
|> I can successfully pass a 1-d array, but 2-d doesn't want to work.
|> Here's what I'm doing (in an abbreviated form)
|>
|> ;; idlprogram.pro ;;
|> pro idlprogram
|> a=fltarr(400,100)
|> b=fltarr(8)
|> m=long(400)
|> n=long(100)
|> l=long(8)
|> ;some code to put data into a and b...
|> dummy = call_external('cfunc.so','_cfunc',a,b,m,n,l)
|> end
|>
|> /* CFUNC.C
|> */
|> void cfunc(int argc, void **argv)
|> {
|> float ** a;
|> float * b;
|> int m,n,l;
|>
|> a = (float **) argv[0]; /* this doesn't work */
A two-dimensional array is still just an array -- no extra level of
indirection is implied. You're treating a as if it was passed to your
routine in the form of an array of pointers to each row (or column).
This is not the case. Only one pointer is passed, and element a(i,j)
can be found in your C program by the expression *(a + i + j*n).
Stein Vidar
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