I get an access violation with this code:

extern(C) char* write(char* text);

void main(string[] args){
	char[] text = "Hello World".dup; //.dup converts string to char[]
	text ~= '\0'; //append

	char* result = write(text.ptr); //you need .ptr
	const(char)[] s = cstr2dstr(result);
	writeln(s);
	readln(); //keep the window open
}

auto cstr2dstr(inout(char)* cstr)
{
	return cstr ? cstr[0 .. strlen(cstr)] : "";
}

--

#include std.stdio;

char* write(char* text){
	return text;
}

On 03.01.2016 13:30, TheDGuy wrote:
> I get an access violation with this code:
>
> extern(C) char* write(char* text);
>
> void main(string[] args){
>      char[] text = "Hello World".dup; //.dup converts string to char[]
>      text ~= '\0'; //append
>
>      char* result = write(text.ptr); //you need .ptr
>      const(char)[] s = cstr2dstr(result);
>      writeln(s);
>      readln(); //keep the window open
> }
>
> auto cstr2dstr(inout(char)* cstr)
> {
>      return cstr ? cstr[0 .. strlen(cstr)] : "";
> }
>
> --
>
> #include std.stdio;
>
> char* write(char* text){
>      return text;
> }
>

Works for me after adding the needed imports and removing the wrong include from the C file. Is this really the actual code you're running? Doesn't your C compiler reject that include? gcc does.

>
> Works for me after adding the needed imports and removing the wrong include from the C file. Is this really the actual code you're running? Doesn't your C compiler reject that include? gcc does.

Okay, i think this C code should work (checked with cpp.sh):

#import <stdio.h>
char* write(char* text){
	return text;
}
int main(void){
    return 0;
}


but i still get the access violation.

On 03.01.2016 14:01, TheDGuy wrote:
> Okay, i think this C code should work (checked with cpp.sh):
>
> #import <stdio.h>
> char* write(char* text){
>      return text;
> }
> int main(void){
>      return 0;
> }

Uh, no. 1) In C it's include, not import. 2) Now you have two main functions, that can't work.

You shouldn't get a segfault, though. You should get some compile/link error. Are you compiling the right files? Can the segfault be from something other than your program?

On 03.01.2016 14:12, anonymous wrote:
> You shouldn't get a segfault, though. You should get some compile/link
> error. Are you compiling the right files? Can the segfault be from
> something other than your program?

Oh, I see what's probably happening:

You compile the D program, but you don't compile and/or don't link the C object file. It segfaults then when trying to call the C function.

You need to compile the C file and pass it to dmd or the linker. For example:

gcc -c -otest.c.o test.c
dmd test.d test.c.o
./test

On Sunday, 3 January 2016 at 12:30:34 UTC, TheDGuy wrote:
> I get an access violation with this code:
>
> ...

There are a few things you can do to improve your code to make it easier to debug.

1. When converting a D string to a char pointer for use with C, use `std.string.toStringz`:

http://dlang.org/phobos/std_string.html#.toStringz

2. When converting a char pointer to a D string use `std.conv.to!(string)`:

http://dlang.org/phobos/std_conv.html#.to

3. Define C-style char pointers in D as `const(char)*`.
4. Don't use the variable name `text` as it conflicts with `std.conv.text`.


I think I've noticed one problem with the code above. You are using `text.ptr`. You shouldn't do that because you are passing a pointer not an array. Just use `text`.

On Sunday, 3 January 2016 at 13:23:25 UTC, Gary Willoughby wrote:
> I think I've noticed one problem with the code above. You are using `text.ptr`. You shouldn't do that because you are passing a pointer not an array. Just use `text`.

Forget this line, my mistake. Use `toStringz` and pass a pointer instead of an array.

On Sunday, 3 January 2016 at 13:25:04 UTC, Gary Willoughby wrote:
> On Sunday, 3 January 2016 at 13:23:25 UTC, Gary Willoughby wrote:
>> I think I've noticed one problem with the code above. You are using `text.ptr`. You shouldn't do that because you are passing a pointer not an array. Just use `text`.
>
> Forget this line, my mistake. Use `toStringz` and pass a pointer instead of an array.

Hi and thanks for your answer. My code looks now like this:

void main(string[] args){
	const(char)* val = "Hello World".std.string.toStringz;
	char* result = write(val);
	const(char)[] s = cstr2dstr(result);
	writeln(s);
	readln(); //keep the window open
}

But now i get the error: "function expected before(), not package std of type void" (refering to line 2).

And if i define the variable 'value' as 'const(char)*' i also have to rewrite my C-function to accept const(char)*...

On Sunday, 3 January 2016 at 19:24:46 UTC, TheDGuy wrote:
> On Sunday, 3 January 2016 at 13:25:04 UTC, Gary Willoughby wrote:
>> On Sunday, 3 January 2016 at 13:23:25 UTC, Gary Willoughby wrote:
>>> I think I've noticed one problem with the code above. You are using `text.ptr`. You shouldn't do that because you are passing a pointer not an array. Just use `text`.
>>
>> Forget this line, my mistake. Use `toStringz` and pass a pointer instead of an array.
>
> Hi and thanks for your answer. My code looks now like this:
>
> void main(string[] args){
> 	const(char)* val = "Hello World".std.string.toStringz;
> 	char* result = write(val);
> 	const(char)[] s = cstr2dstr(result);
> 	writeln(s);
> 	readln(); //keep the window open
> }
>
> But now i get the error: "function expected before(), not package std of type void" (refering to line 2).
>
> And if i define the variable 'value' as 'const(char)*' i also have to rewrite my C-function to accept const(char)*...

Use an import.

import std.string;
import std.conv;

void main(string[] args) {
    auto value  = toStringz("Hello World");
    auto result = write(value);
    auto s      = to!(string)(result);
    writeln(s);
}

Also all string literals in D are zero terminated so you could write the call like this:

auto result = write("Hello World");

>
> Use an import.
>
> import std.string;
> import std.conv;
>
> void main(string[] args) {
>     auto value  = toStringz("Hello World");
>     auto result = write(value);
>     auto s      = to!(string)(result);
>     writeln(s);
> }
>
> Also all string literals in D are zero terminated so you could write the call like this:
>
> auto result = write("Hello World");

Okay, thank you very much!

But now i get the access violation error again.

If i type:
gcc -c -otest.c.o

the 'test.c.o' file is generated but if i type:

dmd main.d test.c.o i get: 'Error: unrecognized file extension o'?