When using pchars, what happens when one does this:

function test(const input: pchar): integer;

Is this a pointer to a pchar? Or is it just a pchar?

i.e. below is bad:
function test(var input: pchar): integer;

So what about a const pchar paramater... Is it a read only pchar, or a read only pointer to a pchar?

It can be either of those. The compiler is free to choose what it does. All you know for sure is that when you try to assign something to "input", the compiler will throw an error.

x
Jonas

Hi everyone,

I would appreciate some advice about the following (I try to be clear and short!):

I am trying to dynamically link a shared library ("libplot.so" from the package: www.gnu.org/software/plotutils ). I do this using "dlopen" and "dlsym". Usually it works very well but this time, I do not understand the "C" prototype in the header file "plot.h":

plPlotterParams * pl_newplparams (void)

The function "pl_newplparams" is supposed create a structure (record) and then return some "pointer" to it. The user is not supposed to access this data directly, so there is NO reference to "plPlotterParams" al all in the header files (plot.h)! How does the C compiler knows what plPlotterParams is then? It just assumes it is a pointer or it looks into the liplot.so file directly? To me this is a mistery!

I now that dlsym will search for the procedure names in the library, but do I have to do that for plPlotterParams as well?

If not, then what type should I use for the return parameter: Pointer? integer? I get an exception as soon as I call the routine. (other routines with simple return types works well of course)

I would apreciate if someone could put me back on the track please!

In order to indicate my level of knowledge, I should mention that so far I could:

1-load the library using "dlopen": error code showed "no error" 2-locate the function using "dlsym": error code showed "no error" 3-made sure that the library is well installed by compiling and running a small C language demo program.

Thank you for reading.

Happy new year

Alain Michaud

amiso

(don't, use unit dynlibs that wrap those)

No idea, I assume that if it is named it must be declared somewhere. However it doesn't really matter if you don't use it, any pointer type will do

I usually use a pointer to an empty record.

It is in a header file, otherwise the C compiler will not compile it either. According to https://bugzilla.redhat.com/bugzilla/ attachment.cgi?id=3380, it may be defined like this in plotter.h:

typedef struct plPlotterParamsStruct
{
int (*setplparam) (struct plPlotterParamsStruct *_plotter_params, const char *parameter, void * value);

   void * plparams[33];

}
PlotterParams;

Jonas