Hi, I'm working with a dll/so created with C++, that has a function which fills an std::ostream, and I need to read it from a FreePascal app using a buffer or TStream.

The C++ method is similar to this:

void myClass::getOutputData(ostream &out);

I wrapped it to be readable from FPC as this:
...
extern "C"{
void getMyOutputData(void * myInstance, void * &stream){

    myClass * lInstance = (myClass *)myInstance;
    lInstance->getOutputData(stream);
  }

}
...

Is there a way to read std::ostream from FPC?

thanks in advance,

No. This kind of stuff doesn't even work between two different C++ compilers.

You probably need to expose this on C level as a proceure that writes "n" bytes to a handle. Then the implementation (in C++) should write that block of mem to the stream.

Thanks Marco, actually the stream contained ASCII data, it was something lika an ObjectPascal's TStringList, so I fill a char* with that data and return it to my program:

//---------- C++ ------------
...
void getTags(void * imagen, char * &aString)
{
    DicomImageHandler * imgHandler = (DicomImageHandler *)imagen;
    std::stringbuf sb;
    std::ostream out(&sb);
    // this fills the "out" stream with data
    imgHandler->getDataset()->print(out);
    aString = new char[strlen(sb.str().c_str()) + 1];
    std::strcpy(aString, sb.str().c_str());
}
...
//---------- End C++ ----------

extern "C"{
void getDicomTags(void * imagen, char * &aString)
{

      getTags(imagen, aString);
  }

}