Oct-files are pieces of C++ code that have been compiled with the Octave API into a dynamically loadable object. They take their name from the file which contains the object which has the extension .oct.
Finding a C++ compiler, using the correct switches, adding the right include paths for header files, etc. is a difficult task. Octave automates this by providing the mkoctfile command with which to build oct-files. The command is available from within Octave or at the shell command line.
The mkoctfile function compiles source code written in C, C++, or Fortran. Depending on the options used with mkoctfile, the compiled code can be called within Octave or can be used as a stand-alone application.
mkoctfile can be called from the shell prompt or from the Octave prompt. Calling it from the Octave prompt simply delegates the call to the shell prompt. The output is stored in the output variable and the exit status in the status variable.
mkoctfile accepts the following options, all of which are optional except for the filename of the code you wish to compile:
Add the include directory DIR to compile commands.
Add the definition DEF to the compiler call.
Add the library LIB to the link command.
Add the library directory DIR to the link command.
Generate dependency files (.d) for C and C++ source files.
Add the run-time path to the link command.
Pass options to the linker like "-Wl,-rpath=…". The quotes are needed since commas are interpreted as command separators.
Pass options to the assembler like "-Wa,OPTION".
Compile but do not link.
Enable debugging options for compilers.
Output filename. Default extension is .oct (or .mex if ‘--mex’ is specified) unless linking a stand-alone executable.
Print configuration variable VAR. There are three categories of variables:
Octave configuration variables that users may override with environment variables. These are used in commands that mkoctfile executes.
ALL_CFLAGS LAPACK_LIBS ALL_CXXFLAGS LDFLAGS ALL_FFLAGS LD_CXX ALL_LDFLAGS LD_STATIC_FLAG BLAS_LIBS LFLAGS CC LIBDIR CFLAGS LIBOCTAVE CPICFLAG LIBOCTINTERP CPPFLAGS OCTAVE_LINK_OPTS CXX OCTINCLUDEDIR CXXFLAGS OCTAVE_LIBS CXXPICFLAG OCTAVE_LINK_DEPS DL_LD OCTLIBDIR DL_LDFLAGS OCT_LINK_DEPS F77 OCT_LINK_OPTS F77_INTEGER8_FLAG RDYNAMIC_FLAG FFLAGS SPECIAL_MATH_LIB FPICFLAG XTRA_CFLAGS INCFLAGS XTRA_CXXFLAGS INCLUDEDIR
Octave configuration variables as above, but currently unused by mkoctfile.
AR DEPEND_EXTRA_SED_PATTERN DEPEND_FLAGS FFTW3F_LDFLAGS FFTW3F_LIBS FFTW3_LDFLAGS FFTW3_LIBS FFTW_LIBS FLIBS LIBS RANLIB READLINE_LIBS
Octave configuration variables that are provided for informational purposes only. Except for ‘OCTAVE_HOME’ and ‘OCTAVE_EXEC_HOME’, users may not override these variables.
If OCTAVE_HOME or OCTAVE_EXEC_HOME are set in the environment, then other variables are adjusted accordingly with OCTAVE_HOME or OCTAVE_EXEC_HOME substituted for the original value of the directory specified by the --prefix or --exec-prefix options that were used when Octave was configured.
API_VERSION LOCALFCNFILEDIR ARCHLIBDIR LOCALOCTFILEDIR BINDIR LOCALSTARTUPFILEDIR CANONICAL_HOST_TYPE LOCALVERARCHLIBDIR DATADIR LOCALVERFCNFILEDIR DATAROOTDIR LOCALVEROCTFILEDIR DEFAULT_PAGER MAN1DIR EXEC_PREFIX MAN1EXT EXEEXT MANDIR FCNFILEDIR OCTAVE_EXEC_HOME IMAGEDIR OCTAVE_HOME INFODIR OCTAVE_VERSION INFOFILE OCTDATADIR LIBEXECDIR OCTDOCDIR LOCALAPIARCHLIBDIR OCTFILEDIR LOCALAPIFCNFILEDIR OCTFONTSDIR LOCALAPIOCTFILEDIR STARTUPFILEDIR LOCALARCHLIBDIR
Link a stand-alone executable file.
Assume we are creating a MEX file. Set the default output extension to ".mex".
Strip the output file.
Echo commands as they are executed.
The file to compile or link. Recognized file types are:
.c C source .cc C++ source .cp C++ source .cpp C++ source .CPP C++ source .cxx C++ source .c++ C++ source .C C++ source .f Fortran source (fixed form) .F Fortran source (fixed form) .f90 Fortran source (free form) .F90 Fortran source (free form) .o object file .a library file
Consider the following short example which introduces the basics of writing a C++ function that can be linked to Octave.
#include <octave/oct.h>
DEFUN_DLD (helloworld, args, nargout,
"Hello World Help String")
{
octave_stdout << "Hello World has "
<< args.length () << " input arguments and "
<< nargout << " output arguments.\n";
// Return empty matrices for any outputs
octave_value_list retval (nargout);
for (int i = 0; i < nargout; i++)
retval(i) = octave_value (Matrix ());
return retval;
} The first critical line is #include <octave/oct.h> which makes available most of the definitions necessary for a C++ oct-file. Note that octave/oct.h is a C++ header and cannot be directly #include’ed in a C source file, nor any other language.
Included by oct.h is a definition for the macro DEFUN_DLD which creates a dynamically loaded function. This macro takes four arguments:
octave_value_list, The return type of functions defined with DEFUN_DLD is always octave_value_list.
There are a couple of important considerations in the choice of function name. First, it must be a valid Octave function name and so must be a sequence of letters, digits, and underscores not starting with a digit. Second, as Octave uses the function name to define the filename it attempts to find the function in, the function name in the DEFUN_DLD macro must match the filename of the oct-file. Therefore, the above function should be in a file helloworld.cc, and would be compiled to an oct-file using the command
mkoctfile helloworld.cc
This will create a file called helloworld.oct that is the compiled version of the function. It should be noted that it is perfectly acceptable to have more than one DEFUN_DLD function in a source file. However, there must either be a symbolic link to the oct-file for each of the functions defined in the source code with the DEFUN_DLD macro or the autoload (Function Files) function should be used.
The rest of the function shows how to find the number of input arguments, how to print through the Octave pager, and how to return from the function. After compiling this function as above, an example of its use is
helloworld (1, 2, 3) -| Hello World has 3 input arguments and 0 output arguments.
Subsequent sections show how to use specific classes from Octave’s core internals. Base classes like dMatrix (a matrix of double values) are found in the directory liboctave/array. The definitive reference for how to use a particular class is the header file itself. However, it is often enough simply to study the examples in the manual in order to be able to use a class.
© 1996–2018 John W. Eaton
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https://octave.org/doc/interpreter/Getting-Started-with-Oct_002dFiles.html