2013-11-06



Do the C programmers know the auxilary tools, their  system  pro-
vides  for  them?  Of course, we all know grep(1), wc(1), and the
like, but do we also know the special development  tools?  Lex(1)
and  yacc(1) are often only known by name, but it's not them that
I mean. I mean size(1), nm(1)  and  ldd(1),  for  instance.  I've
heard about them, but rarely used them.

Today, I've used them to demonstrate the process  of  compilation
to some non-programmers.

1) The C source code in text form and the stored bytes:

     less foo.c
     hd foo.c  # equals: hexdump -C foo.c

2) Compiled to assembler code, displayed in text form:

     cc -S foo.c
     less foo.s

3) Compiled and linked to machine code, examined in various ways:

     cc foo.c
     less a.out
     hd a.out
     nm a.out
     size a.out
     ldd a.out

4) Comparision to the static linked executable:

     gcc --static foo.c
     nm a.out
     size a.out
     ldd a.out

If you are a programmer: Know your tools!



The non-programmers had problems to see the ones and zeros in the
hexdump.  They  simply weren't fluent in hex and didn't wanted to
simply accept that hex is just the same as binary but  more  com-
pact.  They  wanted to actually *see* the single bits. I couldn't
see how this would assure them  more  that  the  computer  really
works  with bits, but I though took five minutes to write a small
program that displays the single bits:

     #include <stdio.h>

     int
     main(int argc, char *argv[])
     {
             int c, i, bytes=0;

             while ((c = getchar()) != EOF) {
                     for (i=7; i>=0; i--) {
                             putchar((c & (1<<i)) ? '1' : '0');
                     }
                     if (++bytes == 8) {
                             bytes = 0;
                             putchar('\n');
                     } else {
                             putchar(' ');
                     }
             }
             if (bytes) {
                     putchar('\n');
             }
             return 0;
     }

The while-loop processes bytes. The  for-loop  splits  the  bytes
into bits and outputs their value. The second half of the program
only does some output formating to ease the readability.



http://marmaro.de/lue/        markus schnalke <meillo@marmaro.de>