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digitalmars.D - Bus error accessing char [] by index - OS X

reply Cam MacRae <cam.macrae gmail.com> writes:
Executing the following example program compiled with


 gdc stringtest.d -o stringtest


I get a bus error on OS X accessing the char array by index (shown in the
comments below). 

I imagine this might be a gdc on OS X issue - any other ideas?

import std.stdio;

void main() {
  char[] firstname
  firstname = "Cam";
  char [] a = firstname, b = firstname;
  a[0] = 'H'; //Bus error here
  writefln(b);
}

cheers,
Cam.
Nov 06 2007
parent reply BCS <ao pathlink.com> writes:
Reply to Cam,


 Executing the following example program compiled with
 

 gdc stringtest.d -o stringtest
 


 I get a bus error on OS X accessing the char array by index (shown in
 the comments below).
 
 I imagine this might be a gdc on OS X issue - any other ideas?
 
 import std.stdio;
 
 void main() {
 char[] firstname
 firstname = "Cam";
 char [] a = firstname, b = firstname;
 a[0] = 'H'; //Bus error here
 writefln(b);
 }
 cheers,
 Cam.


On linux, string literals are in read only memory space. As for OS X...???
Nov 06 2007
parent reply Cam MacRae <cam.macrae gmail.com> writes:
BCS Wrote:


 Reply to Cam,
 
 
 On linux, string literals are in read only memory space. As for OS X...???
 
 


Thanks mate - that could be it. I was just following along the D Transition
guide (http://en.wikibooks.org/wiki/D_Transition_Guide). Perhaps it's out of
date...

c.
Nov 06 2007
parent reply Regan Heath <regan netmail.co.nz> writes:
Cam MacRae wrote:

 BCS Wrote:
 

 Reply to Cam,
 
 
 On linux, string literals are in read only memory space. As for OS
 X...???
 
 


 
 Thanks mate - that could be it. I was just following along the D
 Transition guide (http://en.wikibooks.org/wiki/D_Transition_Guide).
 Perhaps it's out of date...


More like "windows centric" as string literals can be written to on windows.

Simple fix:

         char[] a = firstname.dup, b = firstname;
         a[0] = 'H'; //5

but perhaps dup needs to be introduced or explained before being used 
here...

Regan
Nov 07 2007
parent reply Regan Heath <regan netmail.co.nz> writes:
Regan Heath wrote:

 Cam MacRae wrote:

 BCS Wrote:


 Reply to Cam,


 On linux, string literals are in read only memory space. As for OS
 X...???


 Thanks mate - that could be it. I was just following along the D
 Transition guide (http://en.wikibooks.org/wiki/D_Transition_Guide).
 Perhaps it's out of date...


 
 More like "windows centric" as string literals can be written to on 
 windows.
 
 Simple fix:
 
         char[] a = firstname.dup, b = firstname;
         a[0] = 'H'; //5


Actually, this breaks the example entirely as b is no longer modified by 
a[0] - 'H' oops.

Regan
Nov 07 2007
parent Regan Heath <regan netmail.co.nz> writes:
Regan Heath wrote:

 Regan Heath wrote:

 Cam MacRae wrote:

 BCS Wrote:


 Reply to Cam,


 On linux, string literals are in read only memory space. As for OS
 X...???


 Thanks mate - that could be it. I was just following along the D
 Transition guide (http://en.wikibooks.org/wiki/D_Transition_Guide).
 Perhaps it's out of date...


 More like "windows centric" as string literals can be written to on 
 windows.

 Simple fix:

         char[] a = firstname.dup, b = firstname;
         a[0] = 'H'; //5


 
 Actually, this breaks the example entirely as b is no longer modified by 
 a[0] - 'H' oops.


Here is my suggested fix - I don't have DMD 1.0 to test this with so 
someone else is going to have to edit the wiki (after testing this works!)

import std.stdio;

  void main() {
         char[] firstname, lastname, fullname; //1
         firstname = "Walter".dup; //2
         lastname = "Bright"; //3
         fullname = firstname ~ " " ~ lastname; //4
         writefln("Congratulations on making a great language " ~ 
fullname); //5

         char[] a = firstname, b = firstname;
         a[0] = 'H'; //6
         writefln(b); //prints "Halter"
         writefln("Your name is still %s, right?", fullname); //7, 
prints Walter Bright
  }

    1. Strings are nothing more than character arrays. You'll see more 
about arrays later, but for now, know that character arrays are not a 
special case. The one major note is that D strings are not null 
terminated. Arrays simply keep track of their length.
    2. dup used here to create a copy of the string "Walter" (this is 
because string literals are read-only on some OS's)
    3. No strcpy here. In fact, this is more like reassigning a pointer 
(ie, char *lastname = "Bright").
    4. ~ is the concatenation operator. There is no ambiguity between + 
and ~ for strings.
    5. One way of outputting, although number 7 is better
    6. Since a is really a pointer to firstname, firstname (and hence b) 
actually get modified on this line.
    7. But since fullname was created through concatenation, it remains 
unchanged.
Nov 07 2007