Python/C API gcc compile warning unused variable

Question

I have been trying to embed python into c. I am on Linux Mint 17 and installed python-dev. I have been following the documentation on https://docs.python.org/2/extending/embedding.html I was able to compile the first example using the following.

    #include <Python.h>

    int
    main(int argc, char *argv[])
    {
      Py_SetProgramName(argv[0]);  /* optional but recommended */
      Py_Initialize();
      PyRun_SimpleString("from time import time,ctime\n"
                 "print 'Today is',ctime(time())\n");
      Py_Finalize();
      return 0;
    }

I compiled using gcc with this command:

gcc `python2.7-config --cflags` test.c -o test `python2.7-config --ldflags`

The program compiles fine and works. When I tried to compile the pure embedding example here:

    #include <Python.h>

    int main(int argc, char *argv[])
    {
    PyObject *pName, *pModule, *pDict, *pFunc;
    PyObject *pArgs, *pValue;
    int i;

    if (argc < 3) {
    fprintf(stderr,"Usage: call pythonfile funcname [args]\n");
    return 1;
    }

    Py_Initialize();
    pName = PyString_FromString(argv[1]);
    /* Error checking of pName left out */

    pModule = PyImport_Import(pName);
    Py_DECREF(pName);

     if (pModule != NULL) {
      pFunc = PyObject_GetAttrString(pModule, argv[2]);
    /* pFunc is a new reference */

    if (pFunc && PyCallable_Check(pFunc)) {
        pArgs = PyTuple_New(argc - 3);
        for (i = 0; i < argc - 3; ++i) {
            pValue = PyInt_FromLong(atoi(argv[i + 3]));
            if (!pValue) {
                Py_DECREF(pArgs);
                Py_DECREF(pModule);
                fprintf(stderr, "Cannot convert argument\n");
                return 1;
            }
            /* pValue reference stolen here: */
            PyTuple_SetItem(pArgs, i, pValue);
        }
        pValue = PyObject_CallObject(pFunc, pArgs);
        Py_DECREF(pArgs);
        if (pValue != NULL) {
            printf("Result of call: %ld\n", PyInt_AsLong(pValue));
            Py_DECREF(pValue);
        }
        else {
            Py_DECREF(pFunc);
            Py_DECREF(pModule);
            PyErr_Print();
            fprintf(stderr,"Call failed\n");
            return 1;
        }
        }
         else {
        if (PyErr_Occurred())
            PyErr_Print();
        fprintf(stderr, "Cannot find function \"%s\"\n", argv[2]);
        }
        Py_XDECREF(pFunc);
         Py_DECREF(pModule);
         }
         else {
          PyErr_Print();
           fprintf(stderr, "Failed to load \"%s\"\n", argv[1]);
            return 1;
           }
           Py_Finalize();
            return 0;
             }

I used the same gcc compile command and I got the following error:

    test.c: In function ‘main’:
    test.c:6:33: warning: unused variable ‘pDict’ [-Wunused-variable]
    PyObject *pName, *pModule, *pDict, *pFunc;

Why does this happen and how do I solve this?

Answer 1

It means exactly what the warning says: You are declaring a variable but are not using it anywhere. Just delete pDict and you'll be fine:

PyObject *pName, *pModule, *pFunc;