[gdal-dev] Instructions for a new writing driver?

Wed Jul 19 07:23:29 PDT 2023

Hi,
finally I’ve discovered that the file mmwrlayr.c have to be included as cpp (internally is a C) but the extension is a cpp file.

I don’t understand why so the questions remains open.
In shape driver I see .c and all works but I don’t understand the difference.

Thanks!

De: Abel Pau <a.pau at creaf.uab.cat>
Enviado el: dimecres, 19 de juliol de 2023 10:31
Para: Abel Pau <a.pau at creaf.uab.cat>; gdal-dev at lists.osgeo.org
Asunto: RE: [gdal-dev] Instructions for a new writing driver?

Hi again,

I have a .c file in the makefile added as follow:
# depends from frmts/aigrid, avc
add_gdal_driver(
  TARGET ogr_MiraMon
  SOURCES ogrmiramondatasource.cpp ogrmiramondriver.cpp ogrmiramonlayer.cpp mmwrlayr.c
  BUILTIN)
gdal_standard_includes(ogr_MiraMon)
target_include_directories(ogr_MiraMon PRIVATE $<TARGET_PROPERTY:ogrsf_generic,SOURCE_DIR>)

It makes the .c file appears at the project i VS:

[cid:image001.png at 01D9BA5D.5997B660]

Then I use a function MMReadHeader() in ogrmiramonlayer.cpp but when I try to build an error appears:

ogrmiramonlayer.obj : error LNK2019: unresolved external symbol "int __cdecl MMReadHeader(struct VSIVirtualHandle *,str
uct MiraMonLayerInfo *,struct MM_TH *)" (?MMReadHeader@@YAHPEAUVSIVirtualHandle@@PEAUMiraMonLayerInfo@@PEAUMM_TH@@@Z) r
eferenced in function "public: __cdecl OGRMiraMonLayer::OGRMiraMonLayer(char const *,struct VSIVirtualHandle *,class OG
RSpatialReference const *,int)" (??0OGRMiraMonLayer@@QEAA at PEBDPEAUVSIVirtualHandle@@PEBVOGRSpatialReference@@H at Z) [D:\G
itHub-repository\GDAL\build\GDAL.vcxproj]
    Hint on symbols that are defined and could potentially match:
      MMReadHeader
D:\GitHub-repository\GDAL\build\Debug\gdald.dll : fatal error LNK1120: 1 unresolved externals [D:\GitHub-repository\GDA
L\build\GDAL.vcxproj]

I understand that I have to add the .c file un a library and I try to do it in the makefile:

# miramonlib
if (GDAL_USE_MIRAMONLIB_INTERNAL)
  # ogrmiramon.h miramonfil.h mmwrlayr.c
  add_library(miramonlib OBJECT mmwrlayr.c)
  gdal_standard_includes(miramonlib)
  target_compile_definitions(miramonlib PUBLIC -DSAOffset=vsi_l_offset)
  target_compile_options(miramonlib PRIVATE ${GDAL_C_WARNING_FLAGS})
  if (RENAME_INTERNAL_MIRAMONLIB_SYMBOLS)
    target_compile_definitions(miramonlib PUBLIC -DRENAME_INTERNAL_MIRAMONLIB_SYMBOLS -DSHPAPI_CALL=)
  endif ()
  target_compile_definitions(miramonlib PUBLIC -DUSE_CPL)
  set_property(TARGET miramonlib PROPERTY POSITION_INDEPENDENT_CODE ${GDAL_OBJECT_LIBRARIES_POSITION_INDEPENDENT_CODE})
  target_sources(${GDAL_LIB_TARGET_NAME} PRIVATE $<TARGET_OBJECTS:miramonlib>)
  gdal_add_vendored_lib(ogr_MiraMon miramonlib)
elseif (HAVE_MIRAMONLIB)
  gdal_target_link_libraries(ogr_MiraMon PRIVATE MIRAMONLIB::miramon)
endif ()

I think that this miramonlib is not included and I don’t know how to do that (cause I thought that in had to be done in the makefile).

Can anyone tell me how to add this .c file to use the functions in it in the .cpp files?
THANKS ins advance!

De: gdal-dev <gdal-dev-bounces at lists.osgeo.org<mailto:gdal-dev-bounces at lists.osgeo.org>> En nombre de Abel Pau
Enviado el: dijous, 6 de juliol de 2023 15:01
Para: gdal-dev at lists.osgeo.org<mailto:gdal-dev at lists.osgeo.org>
Asunto: Re: [gdal-dev] Instructions for a new writing driver?

Hi again.
I finally did that and I am happy.

It would be helpful for us to be able to use our C functions to read and write some parts of our format instead of passing all of them to C++.
I’d like doing that but it’s not possible for the moment convert all our code to C++.

My proposal is use a ogrmiramondatasource.cpp, a ogrmiramondriver.cpp and a ogrmiramonlayer.cpp as all of the projects that are created and add our files from C as necessary.
The main goal is adding only the necessary ones.

The question: Is this possible? Can I simply add C files and use that functions from C++ files? Or do GDAL prefer doing it in another way?
Sorry if it is written somewhere else but I couldn’t find it.

Thanks again for your kind help.

De: gdal-dev <gdal-dev-bounces at lists.osgeo.org<mailto:gdal-dev-bounces at lists.osgeo.org>> En nombre de Abel Pau
Enviado el: dimecres, 5 de juliol de 2023 15:13
Para: gdal-dev at lists.osgeo.org<mailto:gdal-dev at lists.osgeo.org>
Asunto: Re: [gdal-dev] Instructions for a new writing driver?

Thanks you both!

De: gdal-dev <gdal-dev-bounces at lists.osgeo.org<mailto:gdal-dev-bounces at lists.osgeo.org>> En nombre de Even Rouault
Enviado el: dimecres, 5 de juliol de 2023 13:59
Para: gdal-dev at lists.osgeo.org<mailto:gdal-dev at lists.osgeo.org>
Asunto: Re: [gdal-dev] Instructions for a new writing driver?

(resending to list)

The CSV driver is actually not that simple to follow since it has tricks to support updates through the OGREditableLayer mechanism. The GMT one (ogr/ogrsf_frmts/gmt) might be a better start for a creation & append only driver. But basically, the only common thing with your own code will be the fact that you have to implement the 2 virtual methods of interest: OGRLayer::CreateField() ,d OGRLayer::ICreateFeature() and declare a few capabilities in OGRLayer::TestCapability()

Unless you want to implement update capabilities (if the format allows it, which is generally not the case for a text based format), it might be simpler to have 2 distinct OGRLayer sub-classes for read-only and write-only operations.
Even
Le 05/07/2023 à 13:21, Laurențiu Nicola via gdal-dev a écrit :
Hi,

I think your best bet would be to take inspiration from an existing driver, like the CSV one (which shouldn't be too different from the hypothetical SPF driver in the docs).

Laurentiu

On Wed, Jul 5, 2023, at 14:17, Abel Pau wrote:

Hi, following instructions about creating a new driver I found that

https://gdal.org/tutorials/vector_driver_tut.html

But I need to create a driver that can also write from any vector it’s own format.

So, the inverse sense of the html I found.

There is any other place I can follow any instructions to fill all function classes to create this part of the driver (the one that writes it’s own format)?

Thanks in advance!

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