Understanding Pointers (with Lego) Part 1

Ahhh pointers.

I’ve been wanting to write a series of posts on pointers for a long time. When I’ve finished, I’ll upload a complete PDF eGuide. In the meantime, enjoy 🙂

Pointers.

A concept that some programmers avoid through fear, others abuse through ignorance, and yet others manage to use with grace and efficiency.

Every programmer who does more than dabble in C and C++ needs to understand this subject. Properly.

This is Part 1 of a multi-part series, and there will be a lovely quiz at the end, which I expect you will all get 100% on after reading my posts, right?

Let’s crack on.

Read moreUnderstanding Pointers (with Lego) Part 1

How To Compile a 32-bit Executable on 64-bit Fedora 19

You know how sometimes you just have to compile and run a 32 bit program on a 64 bit machine, and it’s really annoying that it doesn’t seem to work?

Yeah, me too.

Turns out it’s actually pretty straightforward on Fedora 19.

First of all, you need to use the -m32 build flag. Below I’m using it to compile my program ‘pointers’:

gcc -m32 pointers.c -o pointers

You may run into the following error:

/usr/include/gnu/stubs.h:7:27: fatal error: gnu/stubs-32.h: No such file or directory
# include <gnu/stubs-32.h>
^
compilation terminated.

To fix this you need to install the 32 bit glibc-devel package. You can do this by running:

yum install glibc-devel.i686

Next, you might see this error:

/usr/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-redhat-linux/4.8.2/libgcc_s.so when searching for -lgcc_s
/usr/bin/ld: cannot find -lgcc_s
collect2: error: ld returned 1 exit status

Which means you need to install the 32 bit standard C++ library package. You can do this by running:

yum install libstdc++-devel.i686

Then you can quite happily compile your executable with the -m32 flag, as above:

gcc -m32 pointers.c -o pointers

And, as if by magic, you get a 32 bit exe that runs on your 64 bit machine.

You can use the file command to admire what you’ve made:

[faye@localhost src]$ file pointers
pointers: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), 
for GNU/Linux 2.6.32, BuildID[sha1]=0x39958fed2f5c099ad97fd7512e780066acfb1231, not stripped