Error lvalue required as unary operand

#define PORT 9987

char *ptr = (char *)&PORT;

lvalue required as unary ‘&’ operand

13

from test import test


test()

import cython


def test():
    if cython.compiled:
        print("Yep, I'm compiled.")
    else:
        print("Just a lowly interpreted script.")

    a = None
    b = None

    c = (a, b)

    print(c.count(None) in [0, 2])

➜  ~ /usr/local/lib/python2.7.12/bin/cython -2 -X always_allow_keywords=True -D ./test.py                                                                        
➜  ~ /usr/local/bin/gcc -shared -pthread -pipe -fPIC -fwrapv -Wall -fno-strict-aliasing -O2 -I/usr/local/lib/python2.7.12/include/python2.7 -o ./test.so ./test.c
./test.c: In function ‘__pyx_pf_4test_test’:
./test.c:873:67: error: lvalue required as unary ‘&’ operand
                     (*(__Pyx_PyCFunctionFast)(cfunc)->func)(self, &arg, 1) :
                                                                   ^
./test.c:1212:15: note: in expansion of macro ‘__Pyx_CallUnboundCMethod1’
   __pyx_t_2 = __Pyx_CallUnboundCMethod1(&__pyx_umethod_PyTuple_Type_count, __pyx_v_c, Py_None); if (unlikely(!__pyx_t_2)) __PYX_ERR(0, 15, __pyx_L1_error)
               ^
./test.c:874:79: error: lvalue required as unary ‘&’ operand
                     (*(__Pyx_PyCFunctionFastWithKeywords)(cfunc)->func)(self, &arg, 1, NULL)) :
                                                                               ^
./test.c:1212:15: note: in expansion of macro ‘__Pyx_CallUnboundCMethod1’
   __pyx_t_2 = __Pyx_CallUnboundCMethod1(&__pyx_umethod_PyTuple_Type_count, __pyx_v_c, Py_None); if (unlikely(!__pyx_t_2)) __PYX_ERR(0, 15, __pyx_L1_error)
               ^
./test.c:876:79: error: lvalue required as unary ‘&’ operand
                     (*(__Pyx_PyCFunctionFastWithKeywords)(cfunc)->func)(self, &arg, 1, NULL) :
                                                                               ^
./test.c:1212:15: note: in expansion of macro ‘__Pyx_CallUnboundCMethod1’
   __pyx_t_2 = __Pyx_CallUnboundCMethod1(&__pyx_umethod_PyTuple_Type_count, __pyx_v_c, Py_None); if (unlikely(!__pyx_t_2)) __PYX_ERR(0, 15, __pyx_L1_error)
               ^

import cython


def test():
    if cython.compiled:
        print("Yep, I'm compiled.")
    else:
        print("Just a lowly interpreted script.")

    a = None
    b = None

    c = (a, b)

    d = None
    print(c.count(d) in [0, 2])

➜  ~ /usr/local/lib/python2.7.12/bin/cython -2 -X always_allow_keywords=True -D ./test.py                                                                        
➜  ~ /usr/local/bin/gcc -shared -pthread -pipe -fPIC -fwrapv -Wall -fno-strict-aliasing -O2 -I/usr/local/lib/python2.7.12/include/python2.7 -o ./test.so ./test.c
➜  ~ /usr/local/lib/python2.7.12/bin/python2 ./test_run.py                                
Yep, I'm compiled.
True

➜  ~ /usr/local/lib/python2.7.12/bin/cython --version 
Cython version 0.28a0

C++ has gotten a lot more type-safe than it used to be, if recent impressions are any indication. I mostly dropped it when I moved to Java, but I do minor C++ stuff for AVR chip projects theses days.

Technically, in C++,

malloc()

is invoked by operator

new

undercover, but yes, «new» is preferable in C++.

One thing looks wrong to me, though:

If I’m reading this, pi2 is being initialized to be a pointer to a single byte of memory. It doesn’t match the general context and in any case, it’s generally better NOT to malloc in terms of raw bytes. If you want to malloc space for a byte, do this:

or whatever unit type best fits your needs. Note that this

Actually only allows for a string of 11 characters, since the trailing NUL  character needs a character element as well.

To round out on nit-picking on malloc(), be aware that thanks to memory manager overhead and storage alignment, doing a malloc() on a single byte may actually internally consume 8 or more bytes, so it’s better to find alternative storage environments for small objects.

All of this is moot, however, since in the example code, the malloc() effect is overlaid by a subsequent assignment.

but since pi2 is not free()’d, this is a memory leak!!!

I don’t generally declare multiple variables on a single line myself. For anti-bugging reasons I prefer to declare and initialize each variable on its own line. And since I’m really paranoid, I use

const

where applicable. C does contain traces of the old «constants — aren’t, variables — won’t» so common to older languages.