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In <42fktm$g2p@news.acns.nwu.edu> bcc063@casbah.acns.nwu.edu (UNLISTED) writes:

>i just finished installing the libg++ library for c++ and i want to test the
>compiler to see if it is working. when i try to compile the following little
>test file using gcc,
>i get these errors:
>	collect2: ld returned 2 exit status
>	ld: Undefined symbol
>	  String::length(void)
>	  String::set_to(char *)
>	  String::read(void)
>
>what do these errors mean i did or didn't do? 

You didn't write the routines for these functions in the files you
supplied. If you're planning on using libg++ String routines, don't
use your own home-grown stuff.
-- 
Jonathan Chen                          e-mail : jonc@pinnacle.co.nz
  Pinnacle Software Ltd                Voice  : +64.9.489.7020
  Auckland, New Zealand                Fax    : +64.9.489.7040

bcc063@casbah.acns.nwu.edu (UNLISTED) wrote:

>i just finished installing the libg++ library for c++ and i want to test the
>compiler to see if it is working. when i try to compile the following little
>test file using gcc,
>i get these errors:
>	collect2: ld returned 2 exit status
>	ld: Undefined symbol
>	  String::length(void)
>	  String::set_to(char *)
>	  String::read(void)

>what do these errors mean i did or didn't do? 
>(i'm new at c++)
>below are the files...

>/* this is the beginning of file String.h */
>const int max_string_length = 128;
>class String{
>public:
>  void set_to(char*);
>  int length();
>  int read();
>  void print();

>private:
>  char text[max_string_length+1];
>};
>/* this is the end of file String.h */

You have only "declared" the member functions, set_to, length, read
and printf.  You must "define" them as well.  If they are simple (one
liners) then this can be done within the class instead of the
declarations. . .

#include <stdio.h>
#include <string.h>

class String
{ char text[max_string_length+1);

public:
  void set_to(char *str) { strncpy(text, str, sizeof text); }
  int length() { return strlen(text); }
  void read() { gets(text); }
  void printf() { puts(text); }
};

Simple member functions like these are implicitly "inline" so they
incur no overhead above directly accessing a structure member in C.

Regards,
Andy Robb.

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The errors you got do just pretain to C++.  They pertain to any language
that uses a linker (I think).  The problem is that you made references to
functions you didn't define.  You _declared_ them in your header file, 
but you didn't link in a module where they are defined.

You another file something like this:

String.cc:

#include "String.h"

String::set_to( char *s) {

    strcpy( text, s);
}

String::length() {

    return strlen( text);
}

String::read() {

    return text;
}

String::print() {

    cout << text;
}

You need to compile this file and link it with your program.  An
easy way to do this is:

g++ my_prog.c String.c -o my_prog

Hope this helps.

MikeB

bcc063@casbah.acns.nwu.edu (UNLISTED) writes:

>what do these errors mean i did or didn't do? 

>/* this is the beginning of file String.h */
>const int max_string_length = 128;
>class String{
>public:
>  void set_to(char*);
>  int length();
>  int read();
>  void print();

>private:
>  char text[max_string_length+1];
>};
>/* this is the end of file String.h */

>/* and the beginning of file test.cc */
>#include "String.h"
>#include<stdio.h>

>main(int, char *[])
>{
>  String s, t;
>  s.set_to("hello world");
>  printf("Length of s is %d\n", s.length());
>  printf("Enter string t:	");
>  t.read();
>  printf("Length of t is %d\n",t.length());
>  return 0;
>}
>/* this is the end of file test.cc */

You never defined the member functions. You gave the declarations, but
never the definitions. This is what the linker is complaining about.
The compiler sees just the declarations and write the function calls,
assuming you will link in the called functions. But since you never gave
the definitions of the functions, the linker was not able to write
the machine code for the function calls.

You need a String.cc file that contains the definitions. It should #include
"String.h". You'll compile it separately from test.cc. Then you'll link
test.o and String.o (or whatever your object files are called).

By the way, the main(int, char *[]) is a new twist on an old theme.
I'd recommend int main(). Ignoring the argc and agrv arguments is okay.
-- 
Steve Chapel        schapel@cs.ucsb.edu   |   http://www.cs.ucsb.edu/~schapel
   Senior in Computer Science at the      |   finger -l schapel@eci1.ucsb.edu
University of California, Santa Barbara   |   Finger me for my PGP public key