| Re: CALL_EXTERNAL and memory allocation [message #29680] |
Mon, 11 March 2002 10:03 |
Michael Zingale
Messages: 4
Registered: March 2002
|
Junior Member |
|
|
yes, I forgot to mention that the string that I initialize in IDL is of
length greater than or equal to the length of the string that I am
reading in in the C program. This way I know the memory is allocated.
The example on the website that I pointed to does this.
Mike
James Kuyper wrote:
> Michael Zingale wrote:
>
>> I typically do something like the following:
>>
>>
>> in IDL:
>>
>> string = ' '
>>
>> ierr = call_external('lib.so', 'read_string', string)
>>
>>
>> and in C:
>>
>> IDL_STRING* string = (IDL_STRING *) argv[0];
>>
>> then fill string.s with the string.
>
>
> Are you referring to the 'argv' that appears as a parameter in a C
> main()? That's not necessarily legal. You need to first make sure that:
>
> strlen(argv[0]) > sizeof(IDL_STRING)
>
> Otherwise, you many be overwriting memory that you don't have permission
> to access.
>
|
|
|
|
| Re: CALL_EXTERNAL and memory allocation [message #29682 is a reply to message #29680] |
Mon, 11 March 2002 08:43  |
James Kuyper
Messages: 425
Registered: March 2000
|
Senior Member |
|
|
Michael Zingale wrote:
> I typically do something like the following:
>
>
> in IDL:
>
> string = ' '
>
> ierr = call_external('lib.so', 'read_string', string)
>
>
> and in C:
>
> IDL_STRING* string = (IDL_STRING *) argv[0];
>
> then fill string.s with the string.
Are you referring to the 'argv' that appears as a parameter in a C
main()? That's not necessarily legal. You need to first make sure that:
strlen(argv[0]) > sizeof(IDL_STRING)
Otherwise, you many be overwriting memory that you don't have permission
to access.
|
|
|
|
| Re: CALL_EXTERNAL and memory allocation [message #29693 is a reply to message #29682] |
Sun, 10 March 2002 15:43 |
Michael Zingale
Messages: 4
Registered: March 2002
|
Junior Member |
|
|
I should also point out that I have an example of reading a string from
an HDF5 dataset into IDL via call_external at the bottom of the
following page:
http://www.ucolick.org/~zingale/io_tutorial/
in the file idl_hdf5.tar
Mike
Michael Zingale wrote:
> I typically do something like the following:
>
>
> in IDL:
>
> string = ' '
>
> ierr = call_external('lib.so', 'read_string', string)
>
>
> and in C:
>
> IDL_STRING* string = (IDL_STRING *) argv[0];
>
> then fill string.s with the string.
>
>
> To do an array of strings, it is a little more compilicated. If you do
>
> unklabels = strarr(num),
>
> you must initialize each string with a UNIQUE value, otherwise, IDL
> gives them the same memory address. I do something like this:
>
> unklabels = strarr(nvar)
>
> ; this is important -- each string must be initialized to a unique
> ; 'word', otherwise all the unklabels will share the same address in
> ; memory
> for i = 0, nvar-1 do begin
> unklabels[i] = string(i, format = '(i4)')
> endfor
>
> Then I can fill this in IDL w/o problems.
>
> Mike
>
>
>
>
>
>
> lyubo wrote:
>
>> I have to get back a string from C, and if I have a null string
>> defined in IDL and passed to C it won't work, because there
>> isn't any memory allocated to the string.
>>
>> In general, how can I allocate memory for a string in IDL?
>>
>> lyubo
>>
>>
>>
>>
>>
>>
>>
>
>
|
|
|
|
| Re: CALL_EXTERNAL and memory allocation [message #29694 is a reply to message #29693] |
Sun, 10 March 2002 13:42 |
Michael Zingale
Messages: 4
Registered: March 2002
|
Junior Member |
|
|
I typically do something like the following:
in IDL:
string = ' '
ierr = call_external('lib.so', 'read_string', string)
and in C:
IDL_STRING* string = (IDL_STRING *) argv[0];
then fill string.s with the string.
To do an array of strings, it is a little more compilicated. If you do
unklabels = strarr(num),
you must initialize each string with a UNIQUE value, otherwise, IDL
gives them the same memory address. I do something like this:
unklabels = strarr(nvar)
; this is important -- each string must be initialized to a unique
; 'word', otherwise all the unklabels will share the same address in
; memory
for i = 0, nvar-1 do begin
unklabels[i] = string(i, format = '(i4)')
endfor
Then I can fill this in IDL w/o problems.
Mike
lyubo wrote:
> I have to get back a string from C, and if I have a null string
> defined in IDL and passed to C it won't work, because there
> isn't any memory allocated to the string.
>
> In general, how can I allocate memory for a string in IDL?
>
> lyubo
>
>
>
>
>
>
>
|
|
|
|
| Re: CALL_EXTERNAL and memory allocation [message #29700 is a reply to message #29694] |
Sat, 09 March 2002 09:42 |
Mark Rivers
Messages: 49
Registered: February 2000
|
Member |
|
|
lyubo <lzagorch@cs.wright.edu> wrote in message
news:a6d9nn$76k$1@mercury.wright.edu...
> I have to get back a string from C, and if I have a null string
> defined in IDL and passed to C it won't work, because there
> isn't any memory allocated to the string.
>
> In general, how can I allocate memory for a string in IDL?
I would recommend not passing strings to CALL_EXTERNAL, but rather pass a
byte array, it's easier and more portable, since the IDL string structure
definition changed between IDL 5.4 and 5.5.
In your wrapper routine.
b = bytarr(256) ; Must dimension for maximum string length
s = call_external('my_dll', 'my_funct', b)
; The external C routine places the string in the bytarr 'b', with NULL
termination.
str = string(b) ; Convert from bytarr to string
Mark Rivers
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
