Re: Qt-compatible Channel Access lib

[Jens Eden <eden@bessy2.berlin.ptb.de>]

Ernest L. Williams Jr. wrote:
> On Tue, 2005-10-11 at 16:25 +0200, Jens Eden wrote:
> > Mark,
> >
> > it is possible to link applications compiled with MinGW to
> > dll-Files compiled with MS Visual Studio.
> > So in theory it is possible to link your MinGW/QT-Application to Epics
> > base compiled with MS Visual C++.
> No it is not.  We have already gone down this path.  We are dealing with
> C++ code and the compiler that you use for building EPICS BASE must be
> the same when working with Qt.
>
> We built EPICS BASE with MS C++ and tried to link EPICS libraries with
> the GPLd version of Qt which uses MinGW only; did not work.

It works for me, attached is a small code snippet
(it's just a quick and very dirty hack, to show linking and running
ca_array_get() returns ECA_GETFAIL)
which you can compile with the following command (make sure MinGW is in 
your Path):
g++ -o ca-test.exe ca-test.cpp D:\epics\base-3.14.5\lib\win32-x86\ca.lib

You need the EPICS-dlls in your Path to run it.

That's all I tried, so I don't know, if there are other issues with the
two compilers if developing real world applications.

Did you try to compile the GPLed version of Qt with MS C++?

Jens

*****************
#include <stdio.h>

#ifdef __cplusplus
extern "C" {
#endif
__stdcall int ca_context_create(int);
__stdcall int ca_create_channel(char *, void *, void *, int, void *);
__stdcall int ca_array_get( long, long, void *, void *);
__stdcall int ca_pend_io( double);
__stdcall int ca_flush_io();
#ifdef __cplusplus
}
#endif

# define DBR_DOUBLE 6

int main(void)
{
    int result;
    char *pvname="ringCurrent1";
    char somespace[500];
    void *mychid;
    double doubledata=1.234;

    mychid = (void *)somespace;

    result = ca_context_create(0);
    if (result != 1) {
        printf("CA error (%d) ca_context_create \n", result);
	return 1;
    }
    result = ca_create_channel(pvname, NULL, NULL, 0, mychid);
    if (result != 1) {
        printf("CA error (%d) ca_create_channel \n", result);
	return 1;
    }
    result = ca_flush_io();
    if (result != 1) {
        printf("CA error (%d) ca_pend_io \n", result);
	return 1;
    }
    result = ca_pend_io(1.0);
    if (result != 1) {
        printf("CA error (%d) ca_pend_io \n", result);
	return 1;
    }
    result = ca_array_get(DBR_DOUBLE, 0, mychid, &doubledata);
    if (result != 1) {
        printf("CA error (%d) ca_array_get \n", result);
	//	return 1;
    }
     result = ca_pend_io(1.0);
    if (result != 1) {
        printf("CA error (%d) ca_pend_io \n", result);
	return 1;
    }

    printf("value: %9.5g\n", doubledata);
}