C++ Setup on Linux
Contents
- Compiler
- Other build flags
- Debugging
- Portability Testing
- Clang sanitizers
- Heap Usage (ICU4C)
- Quick Scripts for small test programs
Compiler
For ICU4C 50 or newer the configure
script picks clang
if it is installed, or else gcc
. Clang produces superior error messages and warnings.
Most Linuxes should have clang available to install. On Ubuntu or other Debian-based systems, install it with
sudo apt-get install clang
Debug builds must use compiler option -g
and should not optimize (-O0
is the default). A future version of gcc
might support -Og
as the recommended optimization level for debugging.
Release builds can use -O3
for best performance. See http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html
clang
might even benefit from -O4
where “whole program optimization is done at link time”. See http://developer.apple.com/library/mac/#documentation/Darwin/Reference/Manpages/man1/clang.1.html
Other build flags
On a modern Linux you can configure with CPPFLAGS="-DU_CHARSET_IS_UTF8=1"
.
Debugging
gdb
should work with both out-of-source and in-source builds. If not, double-check with “make VERBOSE=1
” that both .c and .cpp files are compiled with -g
and either -O0
or no -O*anything*
at all.
kdbg
is a reasonable GUI frontend for gdb. It keeps the source code in sync and updates views of variables & memory etc.
- kdbg versions below 2.5.2 do not work with gdb 7.5; you get a message box with “GDB: Reading symbols from…”
- As a workaround,
- Create a
~/.gdbinit
file withset print symbol-loading off
- Start kdbg, open
Settings/Global options
and remove the--nx
argument to gdb.
- Create a
Portability Testing
GitHub pull requests are automatically tested on Windows, Linux with both clang & gcc, and Macintosh. The build results show up as check results on the status page.
Build errors will block the pull request. It’s also useful to check the build logs for new warnings on platforms other than the one used for development.
Clang sanitizers
Clang has built-in santizers to check for several classes of problems. Here are the configure options for building ICU with the address checker:
CPPFLAGS=-fsanitize=address LDFLAGS=-fsanitize=address ./runConfigureICU
--enable-debug --disable-release Linux/clang --disable-renaming
The other available sanitizers are thread
, memory
and undefined
behavior. At the time of this writing, thread and address run cleanly, the others show warnings that have not yet been resolved.
Heap Usage (ICU4C)
HeapTrack is a useful tool for analyzing heap usage of a test program, to check the total heap activity of a particular function or object creation, for example. It will show totals by line in the source, and can move up and down the stack to see more detail.
https://github.com/KDE/heaptrack
To install on Linux,
sudo apt install heaptrack
sudo apt install heaptrack-gui
Quick Scripts for small test programs
I use the following simple scripts to simplify building and debugging small stand-alone programs against ICU, without needing to set up makefiles. They assume a program with a single .cpp file with the same name as the directory in which it resides.
b: build
r: run
d: debug
v: run under valgrind
You will probably need to modify them to reflect where you keep your most commonly used ICU build, and whether you routinely use an out-of-source ICU build.
$ cat \`which b\`
#! /bin/sh
if \[\[ -z "${ICU_HOME}" \]\] ; then
ICU_HOME=$HOME/icu/icu4c
fi
DIR=\`pwd\`
PROG=\`basename $DIR\`
clang++ -g -I $ICU_HOME/source/common -I $ICU_HOME/source/i18n -I
$ICU_HOME/source/io -L$ICU_HOME/source/lib -L$ICU_HOME/source/stubdata -licuuc
-licui18n -licudata -o $PROG $PROG.cpp
$ cat \`which r\`
#! /bin/sh
if \[\[ -z "${ICU_HOME}" \]\] ; then
ICU_HOME=$HOME/icu/icu/icu4c
fi
DIR=\`pwd\`
PROG=\`basename $DIR\`
LD_LIBRARY_PATH=$ICU_HOME/source/lib:$ICU_HOME/source/stubdata
ICU_DATA=$ICU_HOME/source/data/out ./$PROG
cat \`which d\`
#! /bin/sh
if \[\[ -z "${ICU_HOME}" \]\] ; then
ICU_HOME=$HOME/icu/icu/icu4c
fi
DIR=\`pwd\`
PROG=\`basename $DIR\`
LD_LIBRARY_PATH=$ICU_HOME/source/lib:$ICU_HOME/source/stubdata
ICU_DATA=$ICU_HOME/source/data/out gdb ./$PROG
$ cat \`which v\`
#! /bin/sh
if \[\[ -z "${ICU_HOME}" \]\] ; then
ICU_HOME=$HOME/icu/icu/icu4c
fi
DIR=\`pwd\`
PROG=\`basename $DIR\`
LD_LIBRARY_PATH=$ICU_HOME/source/lib:$ICU_HOME/source/stubdata
ICU_DATA=$ICU_HOME/source/data/out valgrind --leak-check=full ./$PROG