<s>
CFLAGS	B-Language
and	O
CXXFLAGS	B-Language
are	O
either	O
the	O
name	O
of	O
environment	O
variables	O
or	O
of	O
Makefile	O
variables	O
that	O
can	O
be	O
set	O
to	O
specify	O
additional	O
switches	O
to	O
be	O
passed	O
to	O
a	O
compiler	B-Language
in	O
the	O
process	O
of	O
building	O
computer	B-Application
software	I-Application
.	O
</s>
<s>
These	O
variables	O
are	O
usually	O
set	O
inside	O
a	O
Makefile	O
and	O
are	O
then	O
appended	O
to	O
the	O
command	O
line	O
when	O
the	O
compiler	B-Language
is	O
invoked	O
.	O
</s>
<s>
Tools	O
like	O
autoconf	B-Application
's	O
./configure	O
script	O
will	O
usually	O
pick	O
them	O
up	O
from	O
the	O
environment	O
and	O
write	O
them	O
into	O
the	O
generated	O
Makefiles	O
.	O
</s>
<s>
Some	O
package	O
install	O
scripts	O
,	O
like	O
SDL	O
,	O
allow	O
CFLAGS	B-Language
settings	O
to	O
override	O
their	O
normal	O
settings	O
(	O
instead	O
of	O
append	O
to	O
them	O
)	O
,	O
so	O
setting	O
CFLAGS	B-Language
can	O
cause	O
harm	O
in	O
this	O
case	O
.	O
</s>
<s>
CFLAGS	B-Language
enables	O
the	O
addition	O
of	O
switches	O
for	O
the	O
C	B-Language
compiler	B-Language
,	O
while	O
CXXFLAGS	B-Language
is	O
meant	O
to	O
be	O
used	O
when	O
invoking	O
a	O
C++	B-Language
compiler	B-Language
.	O
</s>
<s>
Similarly	O
,	O
a	O
variable	O
CPPFLAGS	B-Language
exists	O
with	O
switches	O
to	O
be	O
passed	O
to	O
the	O
C	B-Language
or	I-Language
C++	I-Language
preprocessor	I-Language
.	O
</s>
<s>
Similarly	O
,	O
FFLAGS	O
enables	O
the	O
addition	O
of	O
switches	O
for	O
a	O
Fortran	B-Application
compiler	B-Language
.	O
</s>
<s>
These	O
variables	O
are	O
most	O
commonly	O
used	O
to	O
specify	O
optimization	O
or	O
debugging	O
switches	O
to	O
a	O
compiler	B-Language
,	O
as	O
for	O
example	O
-g	O
,	O
-O2	O
or	O
(	O
GCC-specific	O
)	O
-march	O
=	O
athlon	O
.	O
</s>
