When calling a swig generated function returning std::tuple, i get a swig object of that std::tuple.
Is there a way to use type-maps or something else to extract the values? I have tried changing the code to std::vector for a small portion of the code, and that works. (using %include <std_vector.i> and templates) But i don't want to make too many changes in the C++ part.
Edit: here is a minimal reproducible example:
foo.h
#pragma once
#include <tuple>
class foo
{
private:
double secret1;
double secret2;
public:
foo();
~foo();
std::tuple<double, double> return_thing(void);
};
foo.cpp
#include "foo.h"
#include <tuple>
foo::foo()
{
secret1 = 1;
secret2 = 2;
}
foo::~foo()
{
}
std::tuple<double, double> foo::return_thing(void) {
return {secret1, secret2};
}
foo.i
%module foo
%{
#include"foo.h"
%}
%include "foo.h"
When compiled on my linux using
-:$ swig -python -c++ -o foo_wrap.cpp foo.i
-:$ g++ -c foo.cpp foo_wrap.cpp '-I/usr/include/python3.8' '-fPIC' '-std=c++17' '-I/home/simon/Desktop/test_stack_overflow_tuple'
-:$ g++ -shared foo.o foo_wrap.o -o _foo.so
I can import it in python as shown:
test_module.ipynb
import foo as f
Foo = f.foo()
return_object = Foo.return_thing()
type(return_object)
print(return_object)
Outputs is
SwigPyObject
<Swig Object of type 'std::tuple< double,double > *' at 0x7fb5845d8420>
Hopefully this is more helpful, thank you for responding
To clarify i want to be able to use the values in python something like this:
main.cpp
#include "foo.h"
#include <iostream>
//------------------------------------------------------------------------------'
using namespace std;
int main()
{
foo Foo = foo();
auto [s1, s2] = Foo.return_thing();
cout << s1 << " " << s2 << endl;
}
//------------------------------------------------------------------------------
Github repo if anybody is interested
https://github.com/simon-cmyk/test_stack_overflow_tuple
Our goal is to make something like the following SWIG interface work intuitively:
%module test
%include "std_tuple.i"
%std_tuple(TupleDD, double, double);
%inline %{
std::tuple<double, double> func() {
return std::make_tuple(0.0, 1.0);
}
%}
We want to use this within Python in the following way:
import test
r=test.func()
print(r)
print(dir(r))
r[1]=1234
for x in r:
print(x)
i.e. indexing and iteration should just work.
By re-using some of the pre-processor tricks I used to wrap std::function (which were themselves originally from another answer here on SO) we can define a neat macro that "just wraps" std::tuple for us. Although this answer is Python specific it should in practice be fairly simple to adapt for most other languages too. I'll post my std_tuple.i file, first and then annotate/explain it after:
// [1]
%{
#include <tuple>
#include <utility>
%}
// [2]
#define make_getter(pos, type) const type& get##pos() const { return std::get<pos>(*$self); }
#define make_setter(pos, type) void set##pos(const type& val) { std::get<pos>(*$self) = val; }
#define make_ctorargN(pos, type) , type v##pos
#define make_ctorarg(first, ...) const first& v0 FOR_EACH(make_ctorargN, __VA_ARGS__)
// [3]
#define FE_0(...)
#define FE_1(action,a1) action(0,a1)
#define FE_2(action,a1,a2) action(0,a1) action(1,a2)
#define FE_3(action,a1,a2,a3) action(0,a1) action(1,a2) action(2,a3)
#define FE_4(action,a1,a2,a3,a4) action(0,a1) action(1,a2) action(2,a3) action(3,a4)
#define FE_5(action,a1,a2,a3,a4,a5) action(0,a1) action(1,a2) action(2,a3) action(3,a4) action(4,a5)
#define GET_MACRO(_1,_2,_3,_4,_5,NAME,...) NAME
%define FOR_EACH(action,...)
GET_MACRO(__VA_ARGS__, FE_5, FE_4, FE_3, FE_2, FE_1, FE_0)(action,__VA_ARGS__)
%enddef
// [4]
%define %std_tuple(Name, ...)
%rename(Name) std::tuple<__VA_ARGS__>;
namespace std {
struct tuple<__VA_ARGS__> {
// [5]
tuple(make_ctorarg(__VA_ARGS__));
%extend {
// [6]
FOR_EACH(make_getter, __VA_ARGS__)
FOR_EACH(make_setter, __VA_ARGS__)
size_t __len__() const { return std::tuple_size<std::decay_t<decltype(*$self)>>{}; }
%pythoncode %{
# [7]
def __getitem__(self, n):
if n >= len(self): raise IndexError()
return getattr(self, 'get%d' % n)()
def __setitem__(self, n, val):
if n >= len(self): raise IndexError()
getattr(self, 'set%d' % n)(val)
%}
}
};
}
%enddef
This is just the extra includes we need for our macro to work
These apply to each of the type arguments we supply to our %std_tuple macro invocation, we need to be careful with commas here to keep the syntax correct.
This is the mechanics of our FOR_EACH macro, which invokes each action per argument in our variadic macro argument list
Finally the definition of %std_tuple can begin. Essentially this is manually doing the work of %template for each specialisation of std::tuple we care to name inside of the std namespace.
We use our macro for each magic to declare a constructor with arguments for each element of the correct type. The actual implementation here is the default one from the C++ library which is exactly what we need/want though.
We use our FOR_EACH macro twice to make a member function get0, get1, getN of the correct type of each tuple element and the correct number of them for the template argument size. Likewise for setN. Doing it this way allows the usual SWIG typemaps for double, etc. or whatever types your tuple contains to be applied automatically and correctly for each call to std::get<N>. These are really just an implementation detail, not intended to be part of the public interface, but exposing them makes no real odds.
Finally we need an implementation of __getitem__ and a corresponding __setitem__. These simply look up and call the right getN/setN function on the class and call that instead. We take care to raise IndexError instead of the default exception if an invalid index is used as this will stop iteration correctly when we try to iterate of the tuple.
This is then sufficient that we can run our target code and get the following output:
$ swig3.0 -python -c++ -Wall test.i && g++ -shared -o _test.so test_wrap.cxx -I/usr/include/python3.7 -m32 && python3.7 run.py
<test.TupleDD; proxy of <Swig Object of type 'std::tuple< double,double > *' at 0xf766a260> >
['__class__', '__del__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattr__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__len__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', '__swig_destroy__', '__swig_getmethods__', '__swig_setmethods__', '__weakref__', 'get0', 'get1', 'set0', 'set1', 'this']
0.0
1234.0
Generally this should work as you'd hope in most input/output situations in Python.
There are a few improvements we could look to make:
Implement repr
Implement slicing so that tuple[n:m] type indexing works
Handle unpacking like Python tuples.
Maybe do some more automatic conversions for compatible types?
Avoid calling __len__ for every get/setitem call, either by caching the value in the class itself, or postponing it until the method lookup fails?
When I executed the swig command on my .i file, I am getting an error on an include file.
The error says:
../include/example.h: Error: Extraneous #endif.
The contents of the example.h file is as below:
#ifndef EXAMPLE_H
#define EXAMPLE_H
namespace my_example {
class BaseExample {
public:
virtual ~BaseExample() {}
};
}
#endif /* EXAMPLE_H */
In the above code, the #endif correctly matches with #ifndef.
So, why is swig reporting "Extraneous #endif." ?
I finally found the problem and solved it.
I think, the file had BOM marks in the end of file.
So, I executed
:set nobomb
inside my vim editor, and the error went away.
I want to use some of the functionalities(APIs) of my tcl code in another "c" code file. But i am not getting how to do that especiallly how to link them. For that i have taken a very simple tcl code which contains one API which adds two numbers and prints the sum. Can anybody tell me how can i call this tcl code to get the sum. How can i write a c wrapper that will call this tcl code. Below is my sample tcl program that i am using :
#!/usr/bin/env tclsh8.5
proc add_two_nos { } {
set a 10
set b 20
set c [expr { $a + $b } ]
puts " c is $c ......."
}
To evaluate a script from C code, use Tcl_Eval() or one of its close relatives. In order to use that API, you need to link in the Tcl library, initialize the Tcl library and create an interpreter to hold the execution context. Plus you really ought to do some work to retrieve the result and print it out (printing script errors out is particularly important, as that helps a lot with debugging!)
Thus, you get something like this:
#include <tcl.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char **argv) {
Tcl_Interp *interp;
int code;
char *result;
Tcl_FindExecutable(argv[0]);
interp = Tcl_CreateInterp();
code = Tcl_Eval(interp, "source myscript.tcl; add_two_nos");
/* Retrieve the result... */
result = Tcl_GetString(Tcl_GetObjResult(interp));
/* Check for error! If an error, message is result. */
if (code == TCL_ERROR) {
fprintf(stderr, "ERROR in script: %s\n", result);
exit(1);
}
/* Print (normal) result if non-empty; we'll skip handling encodings for now */
if (strlen(result)) {
printf("%s\n", result);
}
/* Clean up */
Tcl_DeleteInterp(interp);
exit(0);
}
I think i have sloved it out. You were correct. The problem was with the include method that i was using. I have the files tcl.h, tclDecls.h and tclPlatDecls.h included in the c code but these files were not existing in the path /usr/include so i was copying these files to that directory, may be it was not a proper way to do. Finally i have not copied those files to /usr/include and gave the include path while compiling. I have created executable and it is givingthe proper result on terminal. Thanks for your help.
Here is the exact c code i am using :
#include <tcl.h>
#include <tclDecls.h>
#include <tclPlatDecls.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main (int argc, char **argv) {
Tcl_Interp *interp;
int code;
char *result;
printf("inside main function \n");
// Tcl_InitStubs(interp, "8.5", 0);
Tcl_FindExecutable(argv[0]);
interp = Tcl_CreateInterp();
code = Tcl_Eval(interp, "source simple_addition.tcl; add_two_nos");
/* Retrieve the result... */
result = Tcl_GetString(Tcl_GetObjResult(interp));
/* Check for error! If an error, message is result. */
if (code == TCL_ERROR) {
fprintf(stderr, "ERROR in script: %s\n", result);
exit(1);
}
/* Print (normal) result if non-empty; we'll skip handling encodings for now */
if (strlen(result)) {
printf("%s\n", result);
}
/* Clean up */
Tcl_DeleteInterp(interp);
exit(0);
}
And to compile this code and to generate executable file i am using below command :
gcc simple_addition_wrapper_new.c -I/usr/include/tcl8.5/ -ltcl8.5 -o simple_addition_op
I have executed the file simple_addition_op and got below result which was proper
inside main function
c is 30 .......
My special thanks to Donal Fellows and Johannes
I am trying too use my C++ class in PHP. in my C++ code I have declared the typedef as:
typedef unsigned char byte;
so I intended to let SWIG consider my typedef in wrapper class, my interface file is something like this:
%module xxx
typedef unsigned char byte;
%include "xxx.h"
....
%{
typedef unsigned char byte;
#include "xxx.h"
%}
and in my test code I refer to type as:
byte *data;
but I've got the following error:
Fatal error: Class 'unsigned_char' not found in xxx.php
P.S: I also include "stdint.i" in my interface file but got the same error
Any ideas?
I can confirm that the interface you've shown is viable and works for simple cases, e.g. I wrote the following header file to test:
byte *make() { return NULL; }
void consume(byte *data) {}
And used the interface:
%module xxx
typedef unsigned char byte;
%include "xxx.h"
%{
typedef unsigned char byte;
#include "xxx.h"
%}
Which I was able to compile and test with the following PHP:
<?php
include("xxx.php");
$r = xxx::make();
xxx::consume($r);
?>
and it worked as expected.
A few points to note from that though:
In general I would be inclined to write the code you want passed through to the module (i.e. the bits inside the %{ %} before your %include.
Rather than using your own typedef for byte I'd be inclined to use one of the standard int types, e.g. uint8_t
It's not clear from your question quite how you intend to use byte *data - presumably it's an array in which case you'll want to add a little more code to your interface. (Or better still use std::vector<byte> since it's C++):
%module xxx
%{
typedef unsigned char byte;
#include "xxx.h"
%}
%include <carrays.i>
%array_class(byte,ByteArray);
typedef unsigned char byte;
%include "xxx.h"
Which can then be used in PHP as:
$a = new ByteArray(100);
$a->setitem(0, 1);
$a->setitem(1, 2); //...
xxx::consume($a->cast());
ByteArray is a utility class provided by SWIG to hold and wrap a raw C array of bytes.
We have a vendor that has provided us a C++ library and headers, that I'm trying to wrap using SWIG. It appears that they are being too clever by a half with the preprocessor directives:
// top.h
#define DECLARE_WITH_COMMA(a) a,
and then
// foo.h
#include "top.h"
#define MY_TYPES(d) \
d(One) \
d(Two) \
d(Three) \
NumElems
enum MyTypes {
MY_TYPES(DECLARE_WITH_COMMA)
};
Which is all a longwinded way of saying that when I try to run SWIG (version 2.0.4) on "foo.h", I get:
foo.h:12: Error: Syntax error in input(1).
So my question is what are my options here, given that I probably don't want to change the vendor-supplied headers?
SWIG doesn't recurse into nested headers by default, so your .i file should look something like:
%module mymod
%{
#include "foo.h"
%}
%include "top.h"
%include "foo.h"
There is also a SWIG switch:
-includeall - Follow all #include statements
but if you have system headers that may do more than you intend.