calling function from linux executable file

Question

I have python code like this:

import svmlight

training_data = __import__('data').train0
test_data = __import__('data').test0
model = svmlight.learn(training_data, type='classification', verbosity=0)
svmlight.write_model(model, 'my_model.dat')
predictions = svmlight.classify(model, test_data)

Now I have linux executable file svmlight_classify, for above code and all function are also inside this executable. This executable was create from c code using make command.

can I directly call classify() function from svmlight_classify executable file?

mhawke · Accepted Answer · 2014-10-09 03:11:06Z

No, I don't think that you can directly call functions in an executable, but you can call functions in a shared library. You seem to have access to the C source code, so you should be able to build a shared library like this:

$ gcc -c -fPIC -o svmlight_classify.o svmlight_classify.c
$ gcc -shared -Wl,-soname,libsvmlight_classify.so -o libsvmlight_classify.so  svmlight_classify.o

This should produce a shared library named libsvmlight_classify.so. Now you can load and call its functions using ctypes:

from ctypes import cdll

lib = cdll.LoadLibrary('./libsvmlight_classify.so')
lib.classify()

Probably it will be more complicated than the above. For example, there may be arguments that need to be passed to lib.classify() of a type more complicated than int, string etc. Without the function prototype we can't advise, but the above is generally what you need to do.

Vasily Ryabov · Accepted Answer · 2014-10-08 13:58:08Z

1

You can call C functions from DLL using ctypes standard module.

import ctypes
dll = ctypes.CDLL('your.dll') # or 'your.exe'
python_int_returned = dll.YourFunc(ctypes.c_int(3)).value

ctypes.CDLL can also be created for executable (checked it right now). I didn't check it for calling functions. Anyway you need to declare C functions in C++ code with extern "C" statement, because C++ compiler adds some "underscored" prefixes and suffixes into a binary for C++ functions by default (extern "C" turns it off).

Complicated data is often transferred to C code as a memory pointer (ctypes.POINTER can be useful).

answered Oct 8, 2014 at 13:58

Vasily Ryabov

10.1k6 gold badges31 silver badges87 bronze badges

11 Comments

puncrazy Over a year ago

I guess ctype is for windows executable like dll or exe, but in my case, I have linux executable

Vasily Ryabov Over a year ago

It should work for Linux also. Example: testlib = ctypes.CDLL('/full/path/to/testlib.so')

puncrazy Over a year ago

thanks again, I tried this ` dll = ctypes.CDLL('svm_classify')` which gives error OSError: svm_classify: cannot open shared object file: No such file or directory. The file is in same directory and also imported dll

Vasily Ryabov Over a year ago

Can you run it by subprocess.call('svm_classify') ? Full path?

puncrazy Over a year ago

yes, progress. But as svm_classify needs input parameters it gives error Not enough input parameters!

|

Collectives™ on Stack Overflow

calling function from linux executable file

2 Answers 2

Comments

11 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

11 Comments

Your Answer

Sign up or log in

Post as a guest

Related