Hi Michael, On 23 September 2010 00:49, Michael Müller wrote: > > So when the array memory is allocated by the calling function and freed > by another function and you only what to be able to access the elements > using the array braces you should use the static array approach. But I > would define the static array type as follows > TAtomArray = array[0..MaxInt] of TAtom; // or whatever is the allowed maximum > index > to avoid that Pascal will raise a range checking error when you activate > range checking.
Ha, I think a light bulb just came on! :-) So let me see if I got this right. I defined TAtomArray as a static array with a single element. In static arrays, all elements follow each other in sequence in memory. I only know the length of the static array after the C API call, but because I know the memory address of the first element in the array, I can access the other elements too. And because I currently have range-checking disabled, Pascal doesn't complain that I am going over the bounds of my TAtomArray definition. If I got that right, I should then also know how to pass such an array to the C API (which was going to be my next question). The easiest would be to create a static array with a largish size in Pascal (for DND mime types, 30-50 elements should be plenty), then pass the address of element 0 to the C API, and another parameter that specifies the length of the array (only elements with actual data). Once again, thank you very much for taking the time to explain things in such detail. I really helps a lot. As for the differences between static and dynamic arrays, and a string array - i think I'll annotate my FPC Language Reference docs with what you mentioned, or see if Michael van Canneyt could add that info into the official docs so others can benefit too. Out of interest. Do you know if dynamic array elements are in sequence (storage area in memory) too - like static arrays? So could I do the same as above, but instead of using a static array, use a dynamic array, and pass the address of the first element to the C API? As for freeing the array that the C API returned to me... I don't do the freeing, I simply notify the C library when I am done using the array, and the library does the freeing for me. > To prove my explanation you can simply print the memory addresses of > @xdndtypes and > @xdndtypes[0] for a static array and a (initialized?) dynamic array and > you'll get the > same addresses for the static array and different addresses for the dynamic. Indeed, this is what I got. :-) -- Regards, - Graeme - _______________________________________________ fpGUI - a cross-platform Free Pascal GUI toolkit http://opensoft.homeip.net:8080/fpgui/ _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
