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How to use memcpy in Cython

By : François Bit
Date : September 02 2020, 08:00 AM
This might help you The problem is that you are adding c_string and i. The type of i is object. Add cdef int i right before your for loop to force the type of i to be an int.
This compiles and runs for me:
code :
In [1]: !echo "some text\nfor the file" > foo.txt                                                                                                                                              

In [2]: %load_ext cython                                                                                                                                                                       

In [3]: %%cython 
...: from libc.stdlib cimport malloc 
...: from libc.string cimport memcpy 
...: from libc.stdlib cimport atof 
...: with open('foo.txt', 'rb') as fp: 
...:     line = fp.readline().strip() 
...:     content = fp.read() 
...: cdef int nb = len(content) 
...: #print("Hello ", nb) 
...: cdef char* c_string = <char *> malloc((nb + 1) * sizeof(char)) 
...: cdef char* tmp_str = <char *> malloc(4) 
...: memcpy(tmp_str, c_string + 8, 4) 
...: print(atof(tmp_str))    # this line is ok 
...: cdef int i 
...: for i in range(nb): 
...:     memcpy(tmp_str, c_string + i, 4) 

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Cython: ImportError: No module named 'myModule': how to call a cython module containing a cimport to another cython nodu

By : Ivan Chaffardett
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further I'm trying to import a cython module data.pyx into another cython module user.pyx. Everything compile fine, but when I try to call user.pyx in a python module, I am getting the error 'ImportError: No module named data'. , I might be missing something about Cython, but I think it's:
code :
import package.user

When memcpy from this to a new object in a child class, warning "destination for this 'memcpy' call is a pointer to

By : michelle wang
Date : March 29 2020, 07:55 AM
This might help you It means that this will not work. C++ objects should not be copied with the C library's memcpy() function (except in certain limited situations), which knows nothing about C++ classes, their constructors, destructors, virtual methods, and everything else that's in C++ that's not in C.
What you want is a copy constructor. It's job is exactly what you're trying to accomplish: to make a copy of an existing object.
code :
virtual A* copy(){
         B* b=new B(*this);
         return b;

Why does memcpy to int not work after calling memcpy to bool value

By : David Cara Roca
Date : March 29 2020, 07:55 AM
will be helpful for those in need You ignore the padding of your data in a struct.
Take a look on the following simplified example:
code :
struct X
    bool b;
    int i;

int main()
    X x;
    std::cout << "Address of b " << (void*)(&x.b) << std::endl;
    std::cout << "Address of i " << (void*)(&x.i) << std::endl;

second memcpy() attaches previous memcpy() array to it

By : Vvarsha Gupta
Date : March 29 2020, 07:55 AM
this one helps. It looks like you're not null-terminating the string in ipA. The compiler has put the two variables next to one another in memory, so string operations assume that the first null terminator is sometime after the second array (whenever the next 0 occurs in memory).

Coverage.py/Cython - Unable to trace into Cython library in complex project with unittest

By : racoon
Date : March 29 2020, 07:55 AM
help you fix your problem Of course after I wrote it all up the answer was basic carelessness.
Modifying setup.py doesn't recompile the C code automatically and the C code didn't have the CYTHON_TRACE=1 update in it. Once I removed all C/pyd files and reran setup.py it worked.
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