• "Bob W" <nospam aol.com> Apr 13 2005
• brad domain.invalid Apr 13 2005
• "Carlos Santander B." <csantander619 gmail.com> Apr 13 2005
• "Bob W" <nospam aol.com> Apr 14 2005
• "Walter" <newshound digitalmars.com> Apr 15 2005

"Bob W" <nospam aol.com> writes:

Seems that initialized global C variables
cannot be accessed from D, but neither
compiler nor linker are complaining about
attempting it. Is this correct or did I just
miss out something?


Example:


// C code:

extern int a;
static int b=1234;  // global (local to file ...)

int pass(int x) {
  b+=x;  a=b;
  return(b);
}



// D code:

import std.stdio;

extern (C) int a;
extern (C) int b;
extern (C) int pass(int x);

void main() {
  writefln("'pass' returned: %d",pass(1));   // this works
  writefln("Value of a: %d",a);              // this is ok
  writefln("Value of b: %d",b);              // but this one not
}

brad domain.invalid writes:

Bob W wrote:
 Seems that initialized global C variables
 cannot be accessed from D, but neither
 compiler nor linker are complaining about
 attempting it. Is this correct or did I just
 miss out something?
 
 
 Example:
 
 
 // C code:
 
 extern int a;
 static int b=1234;  // global (local to file ...)
 
 int pass(int x) {
   b+=x;  a=b;
   return(b);
 }
 
 
 
 // D code:
 
 import std.stdio;
 
 extern (C) int a;
 extern (C) int b;
 extern (C) int pass(int x);
 
 void main() {
   writefln("'pass' returned: %d",pass(1));   // this works
   writefln("Value of a: %d",a);              // this is ok
   writefln("Value of b: %d",b);              // but this one not
 }
 
 
 


Ie, I imagine that your C code could access D's external int b.

Brad

"Carlos Santander B." <csantander619 gmail.com> writes:

Bob W wrote:
 Seems that initialized global C variables
 cannot be accessed from D, but neither
 compiler nor linker are complaining about
 attempting it. Is this correct or did I just
 miss out something?
 
 
 Example:
 
 
 // C code:
 
 extern int a;
 static int b=1234;  // global (local to file ...)
 
 int pass(int x) {
   b+=x;  a=b;
   return(b);
 }
 
 
 
 // D code:
 
 import std.stdio;
 
 extern (C) int a;
 extern (C) int b;
 extern (C) int pass(int x);
 
 void main() {
   writefln("'pass' returned: %d",pass(1));   // this works
   writefln("Value of a: %d",a);              // this is ok
   writefln("Value of b: %d",b);              // but this one not
 }
 
 
 


Put your extern(C) declarations in another file but do not link it.

-- 
Carlos Santander Bernal

JP2, you'll always live in our minds

"Bob W" <nospam aol.com> writes:

Maybe I should add some more info:


The C code will be compiled (but not linked)
to a D compatible object file (OMF).

 // C code:

 extern int a;
 static int b=1234;  // global (local to file ...)

 int pass(int x) {
  b+=x;  a=b;
  return(b);
 }



The D code will be compiled and linked with
the object file derived form the C code.

 // D code:

 import std.stdio;

 extern (C) int a;
 extern (C) int b;
 extern (C) int pass(int x);

 void main() {
  writefln("'pass' returned: %d",pass(1));   // this works
  writefln("Value of a: %d",a);              // this is ok
  writefln("Value of b: %d",b);              // but this one not
 }



Results:
- 'a' will be generated by the linker and can be
   accessed by the C and the D code, but of
   course it cannot be automatically initialized.

- 'pass()' proves that 'b' is properly initialized
   and globally available to the C code.

- 'b' cannot be accessed by the D code, but
   the linker does not complain about this.
   When attempting to get the value of 'b'
   from the D code, it will always be 0.


Why does that bother me?

I would like to access some functions (no problem)
AND the initialized data of a C program, which I won't
rewrite to D, because it would take too long. Furthermore
I am not keen writing interface functions which make the
data available to D if there is a simpler way to do it.

If the D code is replaced by a C program, the whole
thing works as expected. So I guess there might be
a way to teach D to do the trick.

Any ideas?

"Walter" <newshound digitalmars.com> writes:

"Bob W" <nospam aol.com> wrote in message
news:d3lh01$l0f$1 digitaldaemon.com...
 If the D code is replaced by a C program, the whole
 thing works as expected. So I guess there might be
 a way to teach D to do the trick.

 Any ideas?


Create the following D code, let's call it externa.d, with these contents:

    extern (C) int a;

Then, use it as:

import std.stdio;

 import externa;     // extern (C) int a;
 extern (C) int b;
 extern (C) int pass(int x);

 void main() {
  writefln("'pass' returned: %d",pass(1));   // this works
  writefln("Value of a: %d",a);              // this is ok
  writefln("Value of b: %d",b);              // but this one not
 }

Compile and link, but do not link in externa.obj.