Re: compile error when using selfcode .h file

[Simon Buchan]

fsshl@yahoo.com wrote:
> I am in g++ or gcc 3.4.4 (tested on both linux ubuntu kernel 3.6.8 and
> cygwin 1.5.18-1 dll on window xp-sp2)
>
> I like to test and using the following .h (lib? I do not know yet to
> make it become lib)
>
> http://www.cs.duke.edu/~ola/ap/code/apstring.h
>
> by simple test program
> -------------------------------------------------------
> #include <iostream>
> #include "/home/eric/apstring.h"
>
> using namespace std;
>
> int main() {
>
> apstring name;
>
> cout << "Enter your last name: " << endl;
> cin >> name;
> cout << name;
>
>   return 0;
>
> }
> ---------------------------------------------------------------
> but compiler response error
> ----------
>
> $ g++   pg88.C -o pg88
> In file included from
> /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/backward/iostream.h:31,
>                  from /home/eric/apstring.h:4,
>                  from pg88.C:4:
> /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/backward/backward_warning.h:32:2:
> warning: #warning This file includes at least one deprecated or
> antiquated header. Please consider using one of the 32 headers found in
> section 17.4.1.2 of the C++ standard. Examples include substituting the
> <X> header for the <X.h> header for C++ includes, or <iostream> instead
> of the deprecated header <iostream.h>. To disable this warning use
> -Wno-deprecated.
> /cygdrive/c/DOCUME~1/ERICLI~1/LOCALS~1/Temp/ccKePRMx.o:pg88.C:(.text+0x167):
> undefined reference to `apstring::apstring()'
> /cygdrive/c/DOCUME~1/ERICLI~1/LOCALS~1/Temp/ccKePRMx.o:pg88.C:(.text+0x1a5):
> undefined reference to `operator>>(std::basic_istream<char,
> std::char_traits<char> >&, apstring&)'
> /cygdrive/c/DOCUME~1/ERICLI~1/LOCALS~1/Temp/ccKePRMx.o:pg88.C:(.text+0x1b8):
> undefined reference to `operator<<(std::basic_ostream<char,
> std::char_traits<char> >&, apstring const&)'
> /cygdrive/c/DOCUME~1/ERICLI~1/LOCALS~1/Temp/ccKePRMx.o:pg88.C:(.text+0x1ca):
> undefined reference to `apstring::~apstring()'
> /cygdrive/c/DOCUME~1/ERICLI~1/LOCALS~1/Temp/ccKePRMx.o:pg88.C:(.text+0x1f4):
> undefined reference to `apstring::~apstring()'
> collect2: ld returned 1 exit status
> -------------------------------------------------------------
>
>   thanks in advance any advancer's advice or help
> charles
First off, why?  It clearly states it implements a sub-set of the 
standard C++ string class in the header.  (It also uses pre-standard 
headers, which is why you get those warnings)
If you still want to use it, you need to also compile the source file 
that goes with it (apstring.cpp at the same site) to get the definitions 
of the functions used, which is why it complains it can't find those 
apstring functions when it links
A typical commandline interaction:
# this is a comment
# note the -c option! I use cc as it is not case-sensitive.
# compile the object file with our main definitions
g++ -c pg88.cc -o pg88.o
# compile the object file with the apstring definitions
g++ -c apstring.cpp -o apstring.o
# link into a working application (note the lack of -c!)
g++    pg88.o apstring.o -o pg88

turning apstring into a (static or dynamic library) is probably overkill 
in this case.  Look through the g++ docs for more information.
PS: the above interaction can be compressed into:
g++    pg88.cc apstring.cpp -o pg88
In a reasonably big system, however, this re-compiles every function 
every time, even if it wasn't changed.  Read up on makefiles to make 
(pun intended) this all really easy once it's set up.