Hi, Is there an alternative to the following syntax of accessing a pointer's value: cdef int i = 10 cdef int* ptr = &i ptr[0] = 5 # value of i becomes 5 # *ptr = 5 # does not work print(ptr[0]) The array indexing syntax becomes a bit tedious after a while, especially when I need to modify hundreds of pointer values.
On Fri, 2010-01-08 at 06:48 -0800, Vogon wrote: > Hi, > > Is there an alternative to the following syntax of accessing a > pointer's value: > > > cdef int i = 10 > cdef int* ptr = &i > > ptr[0] = 5 # value of i becomes 5 > > # *ptr = 5 # does not work > > print(ptr[0]) > > > The array indexing syntax becomes a bit tedious after a while, > especially when I need to modify hundreds of pointer values. No. Dag Sverre
A concise answer. Thank you. On Jan 8, 5:05 pm, Dag Sverre Seljebotn <da... <at> student.matnat.uio.no> wrote: > On Fri, 2010-01-08 at 06:48 -0800, Vogon wrote: > > Hi, > > > Is there an alternative to the following syntax of accessing a > > pointer's value: > > > cdef int i = 10 > > cdef int* ptr = &i > > > ptr[0] = 5 # value of i becomes 5 > > > # *ptr = 5 # does not work > > > print(ptr[0]) > > > The array indexing syntax becomes a bit tedious after a while, > > especially when I need to modify hundreds of pointer values. > > No. > > Dag Sverre
I have a problem that is similar but more complicated. In the .pyx file, I have a pointer to a C struct. I need to access the contents of the struct. From within the .pyx file, I have tried: #1 cdef mystruct_t c_struct = <mystruct_t> *(<mystruct_t *> p_c_struct) which gives the error "Expected an identifier or literal" #2 I have also tried: pythonObj.a = p_c_struct->structField which also gives the error "Expected an identifier or literal" #3 I have considered pointer arithmetic but mystruct_t contains a union. What is the proper way to do this? One thing to mention is that my p_c_struct is actually a Python int type that I cast into a pointer on the way in. Thanks in advance! Cass
On Wed, Jul 21, 2010 at 11:39 AM, Cass <cssndrx <at> gmail.com> wrote:
> I have a problem that is similar but more complicated.
>
> In the .pyx file, I have a pointer to a C struct. I need to access the
> contents of the struct.
> From within the .pyx file, I have tried:
>
> #1
> cdef mystruct_t c_struct = <mystruct_t> *(<mystruct_t *> p_c_struct)
> which gives the error "Expected an identifier or literal"
Try
cdef mystruct_t c_struct = p_c_struct[0] # assuming p_c_struct is
of type mystruct_t*
cdef mystruct_t c_struct = (<mystruct_t *>p_c_struct)[0] # otherwise
> #2
> I have also tried:
> pythonObj.a = p_c_struct->structField
> which also gives the error "Expected an identifier or literal"
Cython automatically dereferences for you, just use
p_c_struct.structField
-> is illegal Python/Cython syntax.
> #3
> I have considered pointer arithmetic but mystruct_t contains a union.
(Continue reading)
On Fri, Jan 8, 2010 at 8:15 AM, Vogon <jusa.sj <at> gmail.com> wrote: > A concise answer. Thank you. To elaborate, Python already has meaning attached to the prefix * operator (packing tuples). The index notation gets annoying, but writing Cython is (or at least should be) more like writing Python than writing C. - Robert > On Jan 8, 5:05 pm, Dag Sverre Seljebotn <da... <at> student.matnat.uio.no> > wrote: >> On Fri, 2010-01-08 at 06:48 -0800, Vogon wrote: >> > Hi, >> >> > Is there an alternative to the following syntax of accessing a >> > pointer's value: >> >> > cdef int i = 10 >> > cdef int* ptr = &i >> >> > ptr[0] = 5 # value of i becomes 5 >> >> > # *ptr = 5 # does not work >> >> > print(ptr[0]) >> >> > The array indexing syntax becomes a bit tedious after a while, >> > especially when I need to modify hundreds of pointer values. >>(Continue reading)
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