digitalmars.D.learn - D-DLLs & Python
- Chris (25/25) Feb 19 2013 I have written a DLL that I load into a Python program.
- John Colvin (9/34) Feb 19 2013 D doesn't use null termination for it's strings, strings are
- jerro (1/8) Feb 19 2013 You can use std.conv.to to convert a C string to a D string.
- John Colvin (4/12) Feb 19 2013 Good to know.
- Chris (72/81) Feb 20 2013 I had tried to!string() and the slicing already but to no avail.
- Chris (18/18) Feb 20 2013 I tried extern (C) which has some advantages. However, it still
- Mike Parker (4/22) Feb 20 2013 Your function is being called from Python, correct? Then in
- Chris (13/16) Feb 20 2013 Correct, and it works _now_*! The lines
- bearophile (9/10) Feb 20 2013 Maybe the D wiki should contain info to save some time and
- Chris (10/18) Feb 20 2013 I agree and I am glad that the people on this forum are always
- John Colvin (4/21) Feb 20 2013 yeah, although extern(C) doesn't have to have any braces.
- Chris (5/35) Feb 20 2013 "export" is used in the DLL how-to. I never had to use it for my
I have written a DLL that I load into a Python program.
Everything works fine (DLL is loaded via ctypes, functions can be
called and are executed). Only the string handling is giving me a
bit of a headache. The string in D is always complete garbage. I
have written Python modules in D (with C wrappers) before and got
them to work. But the DLL in D seems to be a completely different
beast. Does anyone have experience with it?
Python uses ctypes, e.g.
myDLL = CDLL("myDLL") / WinDLL("myDLL")
myDLL.printThis(c_char_p("Hello world")) /
myDLL.printThis(create_string_buffer("Hello world"))
The D side looks like like this:
export void printThis(ref char[] str) {
printf("%s\n", str); // prints "Hello World"
writeln(str); // prints garbage
}
OR
export void printThis(char* str) {
printf("%s\n", str); // prints garbage
writeln(str); // prints garbage
}
What am I doing wrong / missing here? I guess it has something to
do with the pointers.
Thanks!
prin
Feb 19 2013
On Tuesday, 19 February 2013 at 16:23:45 UTC, Chris wrote:
I have written a DLL that I load into a Python program.
Everything works fine (DLL is loaded via ctypes, functions can
be called and are executed). Only the string handling is giving
me a bit of a headache. The string in D is always complete
garbage. I have written Python modules in D (with C wrappers)
before and got them to work. But the DLL in D seems to be a
completely different beast. Does anyone have experience with it?
Python uses ctypes, e.g.
myDLL = CDLL("myDLL") / WinDLL("myDLL")
myDLL.printThis(c_char_p("Hello world")) /
myDLL.printThis(create_string_buffer("Hello world"))
The D side looks like like this:
export void printThis(ref char[] str) {
printf("%s\n", str); // prints "Hello World"
writeln(str); // prints garbage
}
OR
export void printThis(char* str) {
printf("%s\n", str); // prints garbage
writeln(str); // prints garbage
}
What am I doing wrong / missing here? I guess it has something
to do with the pointers.
Thanks!
prin
D doesn't use null termination for it's strings, strings are
immutable(char)[]. You can form a D slice from a pointer by going
slice = ptr[0..length]
where length is the length of the array the pointer represents.
You can't just take a c style string and expect writeln to work
with it.
Also, I think you should have extern(C) in the function
definition.
Feb 19 2013
D doesn't use null termination for it's strings, strings are immutable(char)[]. You can form a D slice from a pointer by going slice = ptr[0..length] where length is the length of the array the pointer represents. You can't just take a c style string and expect writeln to work with it.You can use std.conv.to to convert a C string to a D string.
Feb 19 2013
"John Colvin" <john.loughran.colvin gmail.com> On Tuesday, 19 February 2013 at 19:06:47 UTC, jerro wrote:Good to know. If you do know the length beforehand though, slicing will O(1) as opposed to O(n)D doesn't use null termination for it's strings, strings are immutable(char)[]. You can form a D slice from a pointer by going slice = ptr[0..length] where length is the length of the array the pointer represents. You can't just take a c style string and expect writeln to work with it.You can use std.conv.to to convert a C string to a D string.
Feb 19 2013
On Tuesday, 19 February 2013 at 17:40:03 UTC, John Colvin wrote:D doesn't use null termination for it's strings, strings are immutable(char)[]. You can form a D slice from a pointer by going slice = ptr[0..length] where length is the length of the array the pointer represents. You can't just take a c style string and expect writeln to work with it.I had tried to!string() and the slicing already but to no avail. I think it has something to do with pointer and the stack. Here is what I get export void printThis(ref char[] str) { printf("Incoming printf: %s\n", str); writeln(str); writeln(str.ptr); writeln(str[0..5]); writeln(to!string(str.ptr)); writeln(to!string(str.ptr[0..5])); writeln(to!string(str)); // Error! } OUTPUT: Incoming printf: Hello world ☺ 27FBCC ☺ ☺ ☺ Traceback (most recent call last): File "loaddll.py", line 6, in <module> lib.printThis(c_char_p("Hello world")) WindowsError: exception: access violation reading 0x00284000 If I use writefln("%s\n", str) I get the full garbage which starts with ☺ ☺ 0³' ░ï^ ♦ ☺ (←5 8¹' l¹' x ' x ' 1þ→↔A±ôj ░³' .ö→↔☺◄ D0 ► ô→↔ æ"☻C←↔Jô→↔È1←↔ ß"☻¶)"☻ °;5 +Æ→↔á╚h P®h P®h `³' ► P³' 0³' ░ï^ p á╚h ░<$☻ D0 ► \¬▲ P®h ─²' ¬Ø♫▲á╚h P®h á╚h ☺ ☺ P®h EÑ♫▲á╚h ☺ ☺ æ"☻╚Ui Ó("☻hj] └Ui ╣¢♫▲Ô╚♫▲─²' ½] ½] └Ui ' æ"☻Ó("☻ fÉ"☻☺ 4É"☻ ÞJh (←5 á*♥▲½] └Ui H▒ ▲─Ui ♥ p■] ıÏ♫▲êTi ½] ú/5 ' (Ô$☻+¯♫▲ê♀"☻ú/5 └Ui (←5 2┘♫▲½] êTi &^ 3◄▲½] &^ &^ (Ô$☻Ó┌5 ED◄▲(Ô$☻&^ &^ ☺ ú/5ttt®/5 ¤I◄tttú/5 ☺☺ &^ &^ ☺ ' ☺ tttú/5 ▬☻nt&^ ☺ ¨Rtttú/5 ☺ ' ðÚmttt§ç♥tttú/5 ☺ ' |3 ↔☺ ê ' ú/5 ttt Âü☺ !☻ +e▲Q ╚¬$Q +e ▲Q m◄ ↔☻ É/5 ÿ 5 í9┐w Ó²~ X ' ×⌂P¢─ ' U▬ ↔±þÿj ö ' ¬3╚v Ó ²~È ' ‗×┐w Ó²~M∟ºw Ó²~ á ' ıq├w®&> ý ' ┼×┐w¶‼ ↔ Ó ²~ ¶‼ ↔ Ó²~ Actx ☺ ♀3 ▄ ¶ ☺ 4 |☺ ☺ ☻ N´&→ÿ☻ D Ó☻ `☻ ║q2¾ ♣ J î♣ ▲♥ [IY 2 ♥ ═Û╬2Ó♂ B $♀ 6♥ ╚_P8\☼ ^ ╝☼ h♥ D♣(▒$‼ V |‼ ÿ♥ ► ý ☻ ☺ |☺ ð§ ☺ ☻ L↨ á ☺ ♥ ý▲ î♫ ☺ ♦ x- ¶♥ ☻ ♣ î0 ÿ ☻ ♠ $1 ╠ ☻ 1 ☺ Ó2 ( ☻ ♂ 3 ♦ ☺ SsHd, ☺ ☺ ☺ ♠ î ☺ ÿ§ , ^ ^ ☻ $ 8 C : \ W i n d o w s \ W i n S x s \ N´&→∟☺ D d☺ `☻ ☺ ║q2¾─♥ J ►♦ ▲♥ ☻ [IY-0 2 d ♥ ♥ ═Û╬2d B ¿ ^ ♫ h♥ ♣ D♣(▒¿◄ V ↕ ÿ♥ ♠ M i c r o s o f t . W i n d o w s . S y s t e m C o m p a t i b l e l ☺ ♀☺ ð☺ ☻ , ▄☻ º¹Lí$♦╩☺☺ ETC. ETC......Also, I think you should have extern(C) in the function definition.I based the DLL on this how-to: http://dlang.org/dll.html
Feb 20 2013
I tried extern (C) which has some advantages. However, it still
doesn't produce the desired result (tried slicing too).
extern(C) {
export void synthesize(ref char[] str) {
printf("Incoming printf: %s\n", &str);
writefln("writefln %s", &str);
writefln("writefln %s", to!string(&str));
writefln("writefln %s", to!string(str));
}
}
OUTPUT:
Incoming printf: Hello from Python
writefln 2366A34
writefln 2366A34
Traceback (most recent call last):
File "loaddll.py", line 4, in <module>
lib.printThis(c_char_p("Hello from Python"))
WindowsError: [Error -532414463] Windows Error 0xE0440001
Feb 20 2013
On Wednesday, 20 February 2013 at 12:48:53 UTC, Chris wrote:
I tried extern (C) which has some advantages. However, it still
doesn't produce the desired result (tried slicing too).
extern(C) {
export void synthesize(ref char[] str) {
printf("Incoming printf: %s\n", &str);
writefln("writefln %s", &str);
writefln("writefln %s", to!string(&str));
writefln("writefln %s", to!string(str));
}
}
OUTPUT:
Incoming printf: Hello from Python
writefln 2366A34
writefln 2366A34
Traceback (most recent call last):
File "loaddll.py", line 4, in <module>
lib.printThis(c_char_p("Hello from Python"))
WindowsError: [Error -532414463] Windows Error 0xE0440001
Your function is being called from Python, correct? Then in
addition to the extern(C), the argument needs to be a char*, not
a D array or a reference to one.
Feb 20 2013
On Wednesday, 20 February 2013 at 14:05:40 UTC, Mike Parker wrote:Your function is being called from Python, correct? Then in addition to the extern(C), the argument needs to be a char*, not a D array or a reference to one.Correct, and it works _now_*! The lines printf("Incoming printf: %s\n", str); writefln("writefln %s", to!string(str)); Print now: Incoming printf: Hello from Python writefln Hello from Python So the correct signature is extern (C) {export void printThis(char* str);} Thanks you guys! I'm so glad I don't have to write a C-wrapper! *("_now_" because I tried char* with extern (C) before as I would in my other Python modules, but it didn't work for some reason. Must have overlooked something. Mea culpa!).
Feb 20 2013
Chris:
extern (C) {export void printThis(char* str);}
Maybe the D wiki should contain info to save some time and
experiments to people.
Possible alternative syntax:
extern(C) export void printThis(char* str);
Also, think if you want some const:
extern(C) export void printThis(const(char)* str);
Bye,
bearophile
Feb 20 2013
On Wednesday, 20 February 2013 at 14:36:56 UTC, bearophile wrote:Chris:I agree and I am glad that the people on this forum are always willing to help. I will soon be able to write a book about interfacing to D (via C) from various languages, ha ha!extern (C) {export void printThis(char* str);}Maybe the D wiki should contain info to save some time and experiments to people.Possible alternative syntax: extern(C) export void printThis(char* str); Also, think if you want some const: extern(C) export void printThis(const(char)* str);Yep, const is next on my list. By the way, Python could call the functions in the DLL _without_ extern (C). The name would be mangled though, e.g.: lib.D8abairDLL10printThisFxPaZv(...) It wasn't until arguments were passed to D that the problems kicked in.
Feb 20 2013
On Wednesday, 20 February 2013 at 14:28:06 UTC, Chris wrote:On Wednesday, 20 February 2013 at 14:05:40 UTC, Mike Parker wrote:yeah, although extern(C) doesn't have to have any braces. I've never had to use export before, but then that could be a .so/.dylib vs .dll thingYour function is being called from Python, correct? Then in addition to the extern(C), the argument needs to be a char*, not a D array or a reference to one.Correct, and it works _now_*! The lines printf("Incoming printf: %s\n", str); writefln("writefln %s", to!string(str)); Print now: Incoming printf: Hello from Python writefln Hello from Python So the correct signature is extern (C) {export void printThis(char* str);} Thanks you guys! I'm so glad I don't have to write a C-wrapper! *("_now_" because I tried char* with extern (C) before as I would in my other Python modules, but it didn't work for some reason. Must have overlooked something. Mea culpa!).
Feb 20 2013
On Wednesday, 20 February 2013 at 14:43:06 UTC, John Colvin wrote:On Wednesday, 20 February 2013 at 14:28:06 UTC, Chris wrote:You are right of course!On Wednesday, 20 February 2013 at 14:05:40 UTC, Mike Parker wrote:yeah, although extern(C) doesn't have to have any braces.Your function is being called from Python, correct? Then in addition to the extern(C), the argument needs to be a char*, not a D array or a reference to one.Correct, and it works _now_*! The lines printf("Incoming printf: %s\n", str); writefln("writefln %s", to!string(str)); Print now: Incoming printf: Hello from Python writefln Hello from Python So the correct signature is extern (C) {export void printThis(char* str);} Thanks you guys! I'm so glad I don't have to write a C-wrapper! *("_now_" because I tried char* with extern (C) before as I would in my other Python modules, but it didn't work for some reason. Must have overlooked something. Mea culpa!).I've never had to use export before, but then that could be a .so/.dylib vs .dll thing"export" is used in the DLL how-to. I never had to use it for my .so/.dylib modules either. I am new to Windows and it is a very strange beast. Like cooking without pots and pans.
Feb 20 2013