free mind, free soul

Embedded python script reverse.py

def rstring(s):
    i = len(s)-1
    t = ''
    while(i > -1):
        t += s[i]
        i -= 1
    return t

Host C++ source

#include <Python.h>
#include <stdio.h>

int main() {
  PyObject *strret, *mymod, *strfunc, *strargs;
  char* cstrret;

  Py_Initialize();

  mymod = PyImport_ImportModule("reverse");
  if(mymod == NULL)
    printf("no such module!\n");
  strfunc = PyObject_GetAttrString(mymod, "rstring");

  strargs = Py_BuildValue("(s)", "Hello, world");

  strret = PyEval_CallObject(strfunc, strargs);
  PyArg_Parse(strret, "s", &cstrret);
  printf("Reversed string: %s", cstrret);

  return 0;
}

When C++ executes, seg fault happens.

The root cause is that after C++ host initializes the python interpreter, the interpreter can’t find and import the module reverse. Thus mymod is actually a NULL pointer. Why? The path of reverse module it wants to import is not included in $PYTHONPATH.

Two solutions here. One is to add the path of the module in $PYTHONPATH. The other is to add following lines in C++, right before importing module, so that python interpreter can find the module.

   PyRun_SimpleString("import sys");
   PyRun_SimpleString("sys.path.append(\"module_path\")");

The possible reason could be that MinGW can't modify PATH env due to tight security on Vista. cc1plus is located under $MinGW_installdir\libexec\gcc\mingw32\$(gcc_version). Adding this location to $PATH solves the problem.

After installing a Linux distro on a Windows XP system, the Windows' bootloader will be replaced by GRUB or LILO in MBR, which directs user in either Windows or Linux you installed.

The following are the steps to restore XP's bootloader.

1. Restart the computer with Windows XP CD.

2. Choose to repair Windows to enter recovery console.

3. Select the number which represents the Windows system.

3. Type fixmbr. The windows bootloader will be restored in MBR.