[fpc-pascal] DLL call works on FPC 2.6.4 but not with D7

Paul Breneman Paul2006 at BrenemanLabs.com
Wed Jul 2 12:43:01 CEST 2014

On 07/01/2014 04:24 PM, Paul Breneman wrote:
> On 07/01/2014 02:58 PM, Jonas Maebe wrote:
>> On 01/07/14 19:42, Paul Breneman wrote:
>>> I'm doing the same thing in FPC and D7:
>>>        StringLen := 14;
>>>        MyReturnStr := 'test1234567890';
>>>        Status := ps5000aGetUnitInfo( ps5000a_handle, @MyReturnStr[ 0],
>>> StringLen, requiredSize, RInfo);
>> It wrong in both FPC and D7 (and it will also crash on all platforms in
>> the next version of FPC; in the current version, it will only crash on
>> OS X). You are assigning a string constant to a pchar, and then telling
>> the DLL to overwrite it.
>> In current release versions of FPC (where it doesn't crash), that will
>> result in the data of that string constant getting overwritten. This
>> means that if you assign 'test1234567890' somewhere else to a string,
>> that string will actually get the value with which this string was
>> overwritten the last time.
>> Use getmem to allocate writeable memory.
> Thanks Jonas!  That got things working!

There is a 1.2 MB zip file here with the working source code:

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