[ale] gcc errors...

[Omar Loggiodice]

nomad Writes :
:I can do a "gcc compile.c" and it does everything beautifully.
:But when I do a "gcc -c compile.c" and "ld compile.c" I get the
:following:
:
:-rw-r--r--   1 root     root          180 Aug 29 21:54 compile.c
:-rw-r--r--   1 root     root         1092 Aug 29 21:56 compile.o
:{0}:oasis:/root/prog/>ld compile.o
:ld: warning: cannot find entry symbol _start; defaulting to 08048074
:compile.o: In function `main':
:compile.o(.text+0xc): undefined reference to `printf'
:compile.o(.text+0x19): undefined reference to `printf'
:compile.o(.text+0x26): undefined reference to `printf'
:compile.o(.text+0x37): undefined reference to `scanf'
:compile.o(.text+0x44): undefined reference to `printf'
:compile.o(.text+0x55): undefined reference to `printf'
:

   To form an executable from your object file, ld needs to resolve several
   symbols (such as printf and _start). Obviously those two are not defined
   in your object file, so the linker complains and says that it doesn't know
   where to find them (BTW, _start is an implicit initialization
   routine that is called automatically).
   
   If you wanted to link your program separately the best way to do it is to
   do:
   
   gcc -o myexecutable mysource.c

   This calls the linker with the appropiate flags and libraries.
   
   printf is part of the C library (libc.so.XXXXX) in your machine, and there
   are other initialization files that need to be linked in to form an
   executable from your object file. 
   
   If you want to see the real command that is used to link programs, you
can do:

   gcc -v -o h t.o
   
   which will give you an output similar to:
   
   gcc version 2.7.2
 /usr/i486-linux/bin/ld -m elf_i386 -dynamic-linker /lib/ld-linux.so.1 -o h
 /usr/lib/crt1.o /usr/lib/crti.o /usr/lib/crtbegin.o
 -L/usr/lib/gcc-lib/i486-linux/2.7.2 -L/usr/i486-linux/lib t.o -lgcc
 -lc -lgcc /usr/lib/crtend.o /usr/lib/crtn.o

As you can see there are lots of other things that need to be linked with
your object code to form an executable. (-lc is the c library, the crt* files
are initialization and other needed functions, ld-linux.so is the loader of
dynamic libraries, etc...)

As I said before, the best way to link the code (without compiling) is to call
gcc -o myexe mysource.o...this will take care of calling the linker with the
appropiate flags, paths, object files and libraries for your architecture.


Hope it helps......

-- 
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  Omar R.  /__ /_/ /_/ /_/ / /_/ /_/ / /_  /-_  CIS: 74040,1543
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