numpy 2d int array to C array of int pointers using ctypes
I have a function in C that accepts a nxm integer matrix as an array of n int pointers. Each pointer points to the first element of an integer array of size m, so they these arrays can be seen as the rows of the matrix. So for example:
void func(int **matrix, int n, int m);
And in memory, the array looks like array 1 from this page: http://c-faq.com/aryptr/dynmuldimary.html
I want to use this C function from within Python using ctypes. So I imported it and gave it the following argtypes:
func.argtypes = [ctypes.POINTER(ctypes.POINTER(ctypes.c_int)), ctypes.c_int, ctypes.c_int]
Now I want to give the function a numpy 2d array...
Lets say I have a 2d numpy int array:
a = np.random.rand(2,3) * 100
a = a.astype("int")
How can I convert the numpy matrix a to the proper format and vice versa?
I tried using:
a.ctypes.data_as(ctypes.POINTER(ctypes.POINTER(ctypes.c_int)))
But this gives me a sefgault...
python c arrays numpy ctypes
asked Nov 19 '18 at 17:28
user3302735user3302735
165
add a comment |
I have a function in C that accepts a nxm integer matrix as an array of n int pointers. Each pointer points to the first element of an integer array of size m, so they these arrays can be seen as the rows of the matrix. So for example:
void func(int **matrix, int n, int m);
And in memory, the array looks like array 1 from this page: http://c-faq.com/aryptr/dynmuldimary.html
I want to use this C function from within Python using ctypes. So I imported it and gave it the following argtypes:
func.argtypes = [ctypes.POINTER(ctypes.POINTER(ctypes.c_int)), ctypes.c_int, ctypes.c_int]
Now I want to give the function a numpy 2d array...
Lets say I have a 2d numpy int array:
a = np.random.rand(2,3) * 100
a = a.astype("int")
How can I convert the numpy matrix a to the proper format and vice versa?
I tried using:
a.ctypes.data_as(ctypes.POINTER(ctypes.POINTER(ctypes.c_int)))
But this gives me a sefgault...
python c arrays numpy ctypes
asked Nov 19 '18 at 17:28
user3302735user3302735
165
2
Untested, but try something like:rowptrs = np.array([row.ctypes.data for row in a], dtype=np.intp); passrowptrsas the first argument.
– Warren Weckesser
Nov 19 '18 at 18:08
add a comment |
I have a function in C that accepts a nxm integer matrix as an array of n int pointers. Each pointer points to the first element of an integer array of size m, so they these arrays can be seen as the rows of the matrix. So for example:
void func(int **matrix, int n, int m);
And in memory, the array looks like array 1 from this page: http://c-faq.com/aryptr/dynmuldimary.html
I want to use this C function from within Python using ctypes. So I imported it and gave it the following argtypes:
func.argtypes = [ctypes.POINTER(ctypes.POINTER(ctypes.c_int)), ctypes.c_int, ctypes.c_int]
Now I want to give the function a numpy 2d array...
Lets say I have a 2d numpy int array:
a = np.random.rand(2,3) * 100
a = a.astype("int")
How can I convert the numpy matrix a to the proper format and vice versa?
I tried using:
a.ctypes.data_as(ctypes.POINTER(ctypes.POINTER(ctypes.c_int)))
But this gives me a sefgault...
python c arrays numpy ctypes
asked Nov 19 '18 at 17:28
user3302735user3302735
165
I have a function in C that accepts a nxm integer matrix as an array of n int pointers. Each pointer points to the first element of an integer array of size m, so they these arrays can be seen as the rows of the matrix. So for example:
void func(int **matrix, int n, int m);
And in memory, the array looks like array 1 from this page: http://c-faq.com/aryptr/dynmuldimary.html
I want to use this C function from within Python using ctypes. So I imported it and gave it the following argtypes:
func.argtypes = [ctypes.POINTER(ctypes.POINTER(ctypes.c_int)), ctypes.c_int, ctypes.c_int]
Now I want to give the function a numpy 2d array...
Lets say I have a 2d numpy int array:
a = np.random.rand(2,3) * 100
a = a.astype("int")
How can I convert the numpy matrix a to the proper format and vice versa?
I tried using:
a.ctypes.data_as(ctypes.POINTER(ctypes.POINTER(ctypes.c_int)))
But this gives me a sefgault...
python c arrays numpy ctypes
python c arrays numpy ctypes
asked Nov 19 '18 at 17:28
user3302735user3302735
165
asked Nov 19 '18 at 17:28
user3302735user3302735
165
asked Nov 19 '18 at 17:28
user3302735user3302735
165
asked Nov 19 '18 at 17:28
user3302735user3302735
165
asked Nov 19 '18 at 17:28
user3302735user3302735
165
165
2
Untested, but try something like:rowptrs = np.array([row.ctypes.data for row in a], dtype=np.intp); passrowptrsas the first argument.
– Warren Weckesser
Nov 19 '18 at 18:08
add a comment |
2
Untested, but try something like:rowptrs = np.array([row.ctypes.data for row in a], dtype=np.intp); passrowptrsas the first argument.
– Warren Weckesser
Nov 19 '18 at 18:08
2
2
Untested, but try something like:
rowptrs = np.array([row.ctypes.data for row in a], dtype=np.intp); pass rowptrs as the first argument.– Warren Weckesser
Nov 19 '18 at 18:08
Untested, but try something like:
rowptrs = np.array([row.ctypes.data for row in a], dtype=np.intp); pass rowptrs as the first argument.– Warren Weckesser
Nov 19 '18 at 18:08
add a comment |
0
active
oldest
votes
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53379816%2fnumpy-2d-int-array-to-c-array-of-int-pointers-using-ctypes%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
0
active
oldest
votes
0
active
oldest
votes
active
oldest
votes
active
oldest
votes
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53379816%2fnumpy-2d-int-array-to-c-array-of-int-pointers-using-ctypes%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
2
Untested, but try something like:
rowptrs = np.array([row.ctypes.data for row in a], dtype=np.intp); passrowptrsas the first argument.– Warren Weckesser
Nov 19 '18 at 18:08