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

Jonas Maebe jonas.maebe at elis.ugent.be
Tue Jul 1 20:58:33 CEST 2014

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.


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