freebsd-dev/contrib/gcc
Ruslan Bukin a3e762571c Add a minimal gcc config for RISC-V.
This is required to build csu.

Reviewed by:	andrew
Sponsored by:	DARPA, AFRL
Sponsored by:	HEIF5
Differential Revision:	https://reviews.freebsd.org/D5039
2016-01-23 15:33:11 +00:00
..
config Add a minimal gcc config for RISC-V. 2016-01-23 15:33:11 +00:00
cp Revert r289150: 2015-10-12 02:05:25 +00:00
doc GCC: Add a new option "-fstack-protector-strong" 2015-07-30 14:31:09 +00:00
ginclude
acinclude.m4
aclocal.m4
addresses.h
alias.c
alias.h
alloc-pool.c
alloc-pool.h
attribs.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
BASE-VER * Don't give the impression that this compiler is GPLv3. 2011-10-24 20:52:41 +00:00
basic-block.h
bb-reorder.c
bitmap.c
bitmap.h
bt-load.c
builtin-attrs.def
builtin-types.def gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
builtins.c gcc: upstream alignment cleanups. 2013-11-29 18:46:02 +00:00
builtins.def gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
c-aux-info.c
c-common.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
c-common.def
c-common.h gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
c-config-lang.in
c-convert.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
c-cppbuiltin.c GCC: Add a new option "-fstack-protector-strong" 2015-07-30 14:31:09 +00:00
c-decl.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
c-dump.c
c-errors.c
c-format.c Revert r235797. GCC's mis-assumptions has led to incorrect usage of 2012-05-23 23:43:55 +00:00
c-format.h
c-gimplify.c
c-incpath.c gcc: clean some warnings from -Wformat-security 2013-12-20 20:57:13 +00:00
c-incpath.h
c-lang.c
c-lex.c Add support for "d" floating-point suffix, as defined by draft N1312 2013-05-12 15:29:35 +00:00
c-objc-common.c
c-objc-common.h gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
c-omp.c
c-opts.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
c-parser.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
c-pch.c
c-ppoutput.c gcc: Bring updates from Google's enhanced gcc-4.2.1. 2013-11-23 18:32:53 +00:00
c-pragma.c
c-pragma.h
c-pretty-print.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
c-pretty-print.h gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
c-semantics.c
c-tree.h gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
c-typeck.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
c.opt gcc: Add support for -Wmissing-prototypes in C++ 2014-01-26 02:36:06 +00:00
caller-save.c
calls.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
cfg.c gcc: clean some warnings from -Wformat-security 2013-12-20 20:57:13 +00:00
cfganal.c
cfgbuild.c
cfgcleanup.c
cfgexpand.c GCC: Add a new option "-fstack-protector-strong" 2015-07-30 14:31:09 +00:00
cfghooks.c
cfghooks.h
cfglayout.c
cfglayout.h
cfgloop.c
cfgloop.h
cfgloopanal.c
cfgloopmanip.c
cfgrtl.c
cgraph.c
cgraph.h gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
cgraphunit.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
ChangeLog Upgrade of base gcc and libstdc++ to the last GPLv2-licensed revision 2011-03-29 20:53:51 +00:00
ChangeLog-1997
ChangeLog-1998
ChangeLog-1999
ChangeLog-2000
ChangeLog-2001
ChangeLog-2002
ChangeLog-2003
ChangeLog-2004
ChangeLog-2005
ChangeLog-2006
ChangeLog.apple gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
ChangeLog.gcc43 Revert r260073; small diff reduction wrt gcc43 and Apple GCC. 2014-01-02 13:53:53 +00:00
ChangeLog.lib
ChangeLog.tree-ssa
collect2.c gcc: clean some warnings from -Wformat-security 2013-12-20 20:57:13 +00:00
collect2.h
combine.c Fix optimization bug. 2014-01-06 00:52:39 +00:00
common.opt GCC: Add a new option "-fstack-protector-strong" 2015-07-30 14:31:09 +00:00
conditions.h
config.build
config.gcc gcc: configuration fix. 2013-06-24 21:13:58 +00:00
config.host
config.in
configure gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
configure.ac gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
conflict.c
convert.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
convert.h gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
COPYING
COPYING.LIB
coretypes.h
coverage.c gcc: Bring updates from Google's enhanced gcc-4.2.1. 2013-11-23 18:32:53 +00:00
coverage.h
cppdefault.c gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
cppdefault.h
cppspec.c
crtstuff.c Mark __DTOR_LIST__, __EH_FRAME_BEGIN__ and __CTOR_END__ as used to avoid 2010-08-26 13:04:16 +00:00
cse.c Bring in a subset of gcc fixes that were back ported to 2012-05-18 19:02:39 +00:00
cselib.c
cselib.h
cstamp-h.in
DATESTAMP Upgrade of base gcc and libstdc++ to the last GPLv2-licensed revision 2011-03-29 20:53:51 +00:00
dbxout.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
dbxout.h
ddg.c
ddg.h
debug.c
debug.h
defaults.h
DEV-PHASE * Don't give the impression that this compiler is GPLv3. 2011-10-24 20:52:41 +00:00
df-core.c
df-problems.c
df-scan.c
df.h
dfp.c
dfp.h
diagnostic.c
diagnostic.def
diagnostic.h
dojump.c
dominance.c
domwalk.c
domwalk.h
double-int.c
double-int.h
dummy-checksum.c
dwarf2.h Update intree gdb/kgdb to handle 2 dwarf types: 2015-05-17 15:49:38 +00:00
dwarf2asm.c
dwarf2asm.h
dwarf2out.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
dwarf2out.h
dwarf.h
emit-rtl.c gcc: Add support for label attributes and "unavailable" attribute. 2013-12-28 20:30:31 +00:00
emit-rtl.h
emutls.c
errors.c
errors.h
et-forest.c
et-forest.h
except.c
except.h
explow.c
expmed.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
expr.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
expr.h
final.c gcc: Add support for label attributes and "unavailable" attribute. 2013-12-28 20:30:31 +00:00
fix-header.c
fixproto
flags.h gcc: upstream alignment cleanups. 2013-11-29 18:46:02 +00:00
flow.c
fold-const.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
fp-test.c
FREEBSD-deletelist
FREEBSD-libiberty
FREEBSD-upgrade
FREEBSD-Xlist
FSFChangeLog
FSFChangeLog.10
FSFChangeLog.11
function.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
function.h gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
gbl-ctors.h
gcc.c GCC: Add a new option "-fstack-protector-strong" 2015-07-30 14:31:09 +00:00
gcc.h
gccbug.in
gccspec.c
gcov-dump.c
gcov-io.c
gcov-io.h
gcov-iov.c
gcov.c gcc: warnings from -Wformat-security 2013-12-21 19:53:51 +00:00
gcse.c
gdbinit.in
gen-protos.c
genattr.c
genattrtab.c gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
genautomata.c Fix clang warnings. 2011-05-19 15:18:35 +00:00
gencheck.c
genchecksum.c
gencodes.c
genconditions.c
genconfig.c
genconstants.c
genemit.c
genextract.c
genflags.c
gengenrtl.c
gengtype-lex.l Fix clang warnings. 2011-05-19 15:18:35 +00:00
gengtype-yacc.y
gengtype.c
gengtype.h
genmddeps.c
genmodes.c Fix clang warnings. 2011-05-18 21:00:27 +00:00
genmultilib
genopinit.c gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
genoutput.c
genpeep.c
genpreds.c
genrecog.c
gensupport.c
gensupport.h
ggc-common.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
ggc-none.c
ggc-page.c
ggc-zone.c
ggc.h gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
gimple-low.c Revert r259619: 2013-12-20 18:16:02 +00:00
gimplify.c Revert r259619: 2013-12-20 18:16:02 +00:00
glimits.h
global.c
graph.c
graph.h
gstab.h
gsyms.h
gsyslimits.h
gthr-aix.h
gthr-dce.h
gthr-gnat.c
gthr-gnat.h
gthr-lynx.h
gthr-nks.h
gthr-posix95.h gcc: add some configuration and references. 2013-06-24 20:38:27 +00:00
gthr-posix.c
gthr-posix.h
gthr-rtems.h
gthr-single.h
gthr-solaris.h
gthr-tpf.h
gthr-vxworks.h
gthr-win32.h
gthr.h
haifa-sched.c
hard-reg-set.h
hooks.c
hooks.h
host-default.c
hosthooks-def.h
hosthooks.h
hwint.h
ifcvt.c
input.h
insn-addr.h
insn-notes.def
integrate.c
integrate.h
intl.c
intl.h
ipa-cp.c
ipa-inline.c
ipa-prop.c
ipa-prop.h
ipa-pure-const.c Bring in a subset of gcc fixes that were back ported to 2012-05-18 19:02:39 +00:00
ipa-reference.c
ipa-reference.h
ipa-type-escape.c
ipa-type-escape.h
ipa-utils.c Bring in a subset of gcc fixes that were back ported to 2012-05-18 19:02:39 +00:00
ipa-utils.h
ipa.c
jump.c
lambda-code.c
lambda-mat.c
lambda-trans.c
lambda.h
langhooks-def.h gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
langhooks.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
langhooks.h gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
LANGUAGES
lcm.c
libada-mk.in
libfuncs.h
libgcc2.c Upgrade our copy of llvm/clang to 3.4 release. This version supports 2014-02-16 19:44:07 +00:00
libgcc2.h Upgrade our copy of llvm/clang to 3.4 release. This version supports 2014-02-16 19:44:07 +00:00
libgcc-std.ver gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
libgcov.c
limitx.h
limity.h
lists.c
local-alloc.c
longlong.h Fix compilation of this macro under gcc-4.9 for MIPS32. 2015-06-18 13:40:08 +00:00
loop-doloop.c
loop-init.c Revert r260073; small diff reduction wrt gcc43 and Apple GCC. 2014-01-02 13:53:53 +00:00
loop-invariant.c
loop-iv.c
loop-unroll.c
loop-unswitch.c
machmode.def
machmode.h
main.c
Makefile.in gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
mips-tdump.c gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
mips-tfile.c gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
mkconfig.sh
mklibgcc.in gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
mkmap-flat.awk
mkmap-symver.awk
mode-classes.def
mode-switching.c
modulo-sched.c
omp-builtins.def
omp-low.c Revert r259619: 2013-12-20 18:16:02 +00:00
ONEWS
opt-functions.awk
opt-gather.awk
optabs.c gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
optabs.h gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
optc-gen.awk
opth-gen.awk add support to gcc for AES and PCLMUL intrinsics... This addes the 2013-09-03 17:33:29 +00:00
opts-common.c
opts.c gcc: Bring updates from Google's enhanced gcc-4.2.1. 2013-11-23 18:32:53 +00:00
opts.h
output.h Fix clang warnings. 2011-06-18 13:56:33 +00:00
params.c
params.def
params.h
passes.c
pointer-set.c
pointer-set.h
postreload-gcse.c gcc: Fix postreload-gcse treatment of call-clobbered registers. 2013-11-16 01:29:27 +00:00
postreload.c
predict.c
predict.def
predict.h
prefix.c
prefix.h
pretty-print.c
pretty-print.h
print-rtl.c gcc: Add support for label attributes and "unavailable" attribute. 2013-12-28 20:30:31 +00:00
print-tree.c gcc: Add support for label attributes and "unavailable" attribute. 2013-12-28 20:30:31 +00:00
profile.c
protoize.c
read-rtl.c
README.Portability
real.c
real.h
recog.c
recog.h
reg-notes.def
reg-stack.c
regclass.c
regmove.c
regrename.c
regs.h gcc: Fix postreload-gcse treatment of call-clobbered registers. 2013-11-16 01:29:27 +00:00
reload1.c gcc: merge small upstream change. 2013-12-27 15:15:49 +00:00
reload.c
reload.h
reorg.c
resource.c
resource.h
rtl-error.c
rtl-factoring.c
rtl.c
rtl.def gcc: Add support for label attributes and "unavailable" attribute. 2013-12-28 20:30:31 +00:00
rtl.h gcc: Add support for label attributes and "unavailable" attribute. 2013-12-28 20:30:31 +00:00
rtlanal.c gcc: Fix postreload-gcse treatment of call-clobbered registers. 2013-11-16 01:29:27 +00:00
rtlhooks-def.h
rtlhooks.c
sbitmap.c
sbitmap.h
scan-decls.c
scan-types.sh
scan.c
scan.h
sched-deps.c
sched-ebb.c
sched-int.h
sched-rgn.c
sched-vis.c gcc: more diff reductions against Apple GCC. 2013-12-20 14:56:52 +00:00
sdbout.c
sdbout.h
see.c
SERVICE
simplify-rtx.c gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
sort-protos
sreal.c
sreal.h
stab.def
statistics.h
stmt.c gcc: Add support for label attributes and "unavailable" attribute. 2013-12-28 20:30:31 +00:00
stor-layout.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
stringpool.c
struct-equiv.c
stub-objc.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
sync-builtins.def
sys-protos.h
sys-types.h
system.h
target-def.h gcc: more diff reductions against Apple GCC. 2013-12-20 14:56:52 +00:00
target.h gcc: more diff reductions against Apple GCC. 2013-12-20 14:56:52 +00:00
targhooks.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
targhooks.h Upgrade of base gcc and libstdc++ to the last GPLv2-licensed revision 2011-03-29 20:53:51 +00:00
timevar.c
timevar.def
timevar.h
tlink.c gcc: clean some warnings from -Wformat-security 2013-12-20 20:57:13 +00:00
toplev.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
toplev.h gcc: Add support for label attributes and "unavailable" attribute. 2013-12-28 20:30:31 +00:00
tracer.c
tree-browser.c
tree-browser.def
tree-cfg.c gcc: Add support for label attributes and "unavailable" attribute. 2013-12-28 20:30:31 +00:00
tree-cfgcleanup.c
tree-chrec.c
tree-chrec.h
tree-complex.c
tree-data-ref.c
tree-data-ref.h
tree-dfa.c
tree-dump.c gcc: more diff reductions against Apple GCC. 2013-12-20 14:56:52 +00:00
tree-dump.h
tree-eh.c
tree-flow-inline.h
tree-flow.h gcc: Bring updates from Google's enhanced gcc-4.2.1. 2013-11-23 18:32:53 +00:00
tree-gimple.c Revert r259619: 2013-12-20 18:16:02 +00:00
tree-gimple.h gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
tree-if-conv.c Upgrade of base gcc and libstdc++ to the last GPLv2-licensed revision 2011-03-29 20:53:51 +00:00
tree-inline.c Revert r259619: 2013-12-20 18:16:02 +00:00
tree-inline.h
tree-into-ssa.c
tree-iterator.c
tree-iterator.h
tree-loop-linear.c
tree-mudflap.c
tree-mudflap.h
tree-nested.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
tree-nomudflap.c
tree-nrv.c
tree-object-size.c
tree-optimize.c
tree-outof-ssa.c
tree-pass.h
tree-phinodes.c
tree-pretty-print.c Revert r259619: 2013-12-20 18:16:02 +00:00
tree-profile.c
tree-scalar-evolution.c
tree-scalar-evolution.h
tree-sra.c
tree-ssa-address.c Revert r260073; small diff reduction wrt gcc43 and Apple GCC. 2014-01-02 13:53:53 +00:00
tree-ssa-alias-warnings.c gcc: Bring updates from Google's enhanced gcc-4.2.1. 2013-11-23 18:32:53 +00:00
tree-ssa-alias.c Revert r259619: 2013-12-20 18:16:02 +00:00
tree-ssa-ccp.c Bring a couple of fixes for gcc optimizations. 2012-06-21 16:49:20 +00:00
tree-ssa-copy.c
tree-ssa-copyrename.c
tree-ssa-dce.c Revert r259619: 2013-12-20 18:16:02 +00:00
tree-ssa-dom.c
tree-ssa-dse.c
tree-ssa-forwprop.c
tree-ssa-live.c
tree-ssa-live.h
tree-ssa-loop-ch.c
tree-ssa-loop-im.c
tree-ssa-loop-ivcanon.c
tree-ssa-loop-ivopts.c
tree-ssa-loop-manip.c
tree-ssa-loop-niter.c
tree-ssa-loop-prefetch.c
tree-ssa-loop-unswitch.c
tree-ssa-loop.c
tree-ssa-math-opts.c
tree-ssa-operands.c Revert r259619: 2013-12-20 18:16:02 +00:00
tree-ssa-operands.h
tree-ssa-phiopt.c
tree-ssa-pre.c Bring a couple of fixes for gcc optimizations. 2012-06-21 16:49:20 +00:00
tree-ssa-propagate.c gcc: another round of merges from the gcc pre-43 branch. 2013-11-21 16:38:57 +00:00
tree-ssa-propagate.h
tree-ssa-reassoc.c
tree-ssa-sink.c
tree-ssa-structalias.c Revert r259619: 2013-12-20 18:16:02 +00:00
tree-ssa-structalias.h
tree-ssa-threadedge.c
tree-ssa-threadupdate.c
tree-ssa-uncprop.c
tree-ssa.c
tree-ssanames.c
tree-stdarg.c
tree-stdarg.h
tree-tailcall.c
tree-vect-analyze.c Upgrade of base gcc and libstdc++ to the last GPLv2-licensed revision 2011-03-29 20:53:51 +00:00
tree-vect-generic.c
tree-vect-patterns.c Fix clang warnings. 2011-05-22 22:17:06 +00:00
tree-vect-transform.c
tree-vectorizer.c
tree-vectorizer.h
tree-vn.c
tree-vrp.c gcc: Bring updates from Google's enhanced gcc-4.2.1. 2013-11-23 18:32:53 +00:00
tree.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
tree.def gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
tree.h gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
treestruct.def
tsystem.h
typeclass.h
unwind-c.c
unwind-compat.c
unwind-compat.h
unwind-dw2-fde-compat.c
unwind-dw2-fde-darwin.c
unwind-dw2-fde-glibc.c
unwind-dw2-fde.c
unwind-dw2-fde.h
unwind-dw2.c unwind-d2 build workaround for arm64 2015-03-31 13:37:32 +00:00
unwind-dw2.h
unwind-generic.h
unwind-pe.h
unwind-sjlj.c
unwind.inc
value-prof.c
value-prof.h
var-tracking.c Bring in a subset of gcc fixes that were back ported to 2012-05-18 19:02:39 +00:00
varasm.c gcc: Add support for Apple's Block extension 2014-01-05 00:43:28 +00:00
varray.c
varray.h
vec.c
vec.h
vecprim.h
version.c With the move away from GNATS, point end users to a better web page 2014-06-14 18:45:40 +00:00
version.h
vmsdbg.h
vmsdbgout.c
web.c
xcoff.h
xcoffout.c
xcoffout.h

Copyright (C) 2000, 2003 Free Software Foundation, Inc.

This file is intended to contain a few notes about writing C code
within GCC so that it compiles without error on the full range of
compilers GCC needs to be able to compile on.

The problem is that many ISO-standard constructs are not accepted by
either old or buggy compilers, and we keep getting bitten by them.
This knowledge until know has been sparsely spread around, so I
thought I'd collect it in one useful place.  Please add and correct
any problems as you come across them.

I'm going to start from a base of the ISO C90 standard, since that is
probably what most people code to naturally.  Obviously using
constructs introduced after that is not a good idea.

For the complete coding style conventions used in GCC, please read
http://gcc.gnu.org/codingconventions.html


String literals
---------------

Irix6 "cc -n32" and OSF4 "cc" have problems with constant string
initializers with parens around it, e.g.

const char string[] = ("A string");

This is unfortunate since this is what the GNU gettext macro N_
produces.  You need to find a different way to code it.

Some compilers like MSVC++ have fairly low limits on the maximum
length of a string literal; 509 is the lowest we've come across.  You
may need to break up a long printf statement into many smaller ones.


Empty macro arguments
---------------------

ISO C (6.8.3 in the 1990 standard) specifies the following:

If (before argument substitution) any argument consists of no
preprocessing tokens, the behavior is undefined.

This was relaxed by ISO C99, but some older compilers emit an error,
so code like

#define foo(x, y) x y
foo (bar, )

needs to be coded in some other way.


free and realloc
----------------

Some implementations crash upon attempts to free or realloc the null
pointer.  Thus if mem might be null, you need to write

  if (mem)
    free (mem);


Trigraphs
---------

You weren't going to use them anyway, but some otherwise ISO C
compliant compilers do not accept trigraphs.


Suffixes on Integer Constants
-----------------------------

You should never use a 'l' suffix on integer constants ('L' is fine),
since it can easily be confused with the number '1'.


			Common Coding Pitfalls
			======================

errno
-----

errno might be declared as a macro.


Implicit int
------------

In C, the 'int' keyword can often be omitted from type declarations.
For instance, you can write

  unsigned variable;

as shorthand for

  unsigned int variable;

There are several places where this can cause trouble.  First, suppose
'variable' is a long; then you might think

  (unsigned) variable

would convert it to unsigned long.  It does not.  It converts to
unsigned int.  This mostly causes problems on 64-bit platforms, where
long and int are not the same size.

Second, if you write a function definition with no return type at
all:

  operate (int a, int b)
  {
    ...
  }

that function is expected to return int, *not* void.  GCC will warn
about this.

Implicit function declarations always have return type int.  So if you
correct the above definition to

  void
  operate (int a, int b)
  ...

but operate() is called above its definition, you will get an error
about a "type mismatch with previous implicit declaration".  The cure
is to prototype all functions at the top of the file, or in an
appropriate header.

Char vs unsigned char vs int
----------------------------

In C, unqualified 'char' may be either signed or unsigned; it is the
implementation's choice.  When you are processing 7-bit ASCII, it does
not matter.  But when your program must handle arbitrary binary data,
or fully 8-bit character sets, you have a problem.  The most obvious
issue is if you have a look-up table indexed by characters.

For instance, the character '\341' in ISO Latin 1 is SMALL LETTER A
WITH ACUTE ACCENT.  In the proper locale, isalpha('\341') will be
true.  But if you read '\341' from a file and store it in a plain
char, isalpha(c) may look up character 225, or it may look up
character -31.  And the ctype table has no entry at offset -31, so
your program will crash.  (If you're lucky.)

It is wise to use unsigned char everywhere you possibly can.  This
avoids all these problems.  Unfortunately, the routines in <string.h>
take plain char arguments, so you have to remember to cast them back
and forth - or avoid the use of strxxx() functions, which is probably
a good idea anyway.

Another common mistake is to use either char or unsigned char to
receive the result of getc() or related stdio functions.  They may
return EOF, which is outside the range of values representable by
char.  If you use char, some legal character value may be confused
with EOF, such as '\377' (SMALL LETTER Y WITH UMLAUT, in Latin-1).
The correct choice is int.

A more subtle version of the same mistake might look like this:

  unsigned char pushback[NPUSHBACK];
  int pbidx;
  #define unget(c) (assert(pbidx < NPUSHBACK), pushback[pbidx++] = (c))
  #define get(c) (pbidx ? pushback[--pbidx] : getchar())
  ...
  unget(EOF);

which will mysteriously turn a pushed-back EOF into a SMALL LETTER Y
WITH UMLAUT.


Other common pitfalls
---------------------

o Expecting 'plain' char to be either sign or unsigned extending.

o Shifting an item by a negative amount or by greater than or equal to
  the number of bits in a type (expecting shifts by 32 to be sensible
  has caused quite a number of bugs at least in the early days).

o Expecting ints shifted right to be sign extended.

o Modifying the same value twice within one sequence point.

o Host vs. target floating point representation, including emitting NaNs
  and Infinities in a form that the assembler handles.

o qsort being an unstable sort function (unstable in the sense that
  multiple items that sort the same may be sorted in different orders
  by different qsort functions).

o Passing incorrect types to fprintf and friends.

o Adding a function declaration for a module declared in another file to
  a .c file instead of to a .h file.