компилятор C и C ++ проекта GNU (GNU project C and C++ compiler)
Параметры подробно (Options detail)
Controlling C Dialect
The following options control the dialect of C (or languages
derived from C, such as C++, Objective-C and Objective-C++) that
the compiler accepts:
-ansi
In C mode, this is equivalent to -std=c90. In C++ mode, it is
equivalent to -std=c++98.
This turns off certain features of GCC that are incompatible
with ISO C90 (when compiling C code), or of standard C++
(when compiling C++ code), such as the "asm" and "typeof"
keywords, and predefined macros such as "unix" and "vax" that
identify the type of system you are using. It also enables
the undesirable and rarely used ISO trigraph feature. For
the C compiler, it disables recognition of C++ style //
comments as well as the "inline" keyword.
The alternate keywords "__asm__", "__extension__",
"__inline__" and "__typeof__" continue to work despite -ansi.
You would not want to use them in an ISO C program, of
course, but it is useful to put them in header files that
might be included in compilations done with -ansi. Alternate
predefined macros such as "__unix__" and "__vax__" are also
available, with or without -ansi.
The -ansi option does not cause non-ISO programs to be
rejected gratuitously. For that, -Wpedantic is required in
addition to -ansi.
The macro "__STRICT_ANSI__" is predefined when the -ansi
option is used. Some header files may notice this macro and
refrain from declaring certain functions or defining certain
macros that the ISO standard doesn't call for; this is to
avoid interfering with any programs that might use these
names for other things.
Functions that are normally built in but do not have
semantics defined by ISO C (such as "alloca" and "ffs") are
not built-in functions when -ansi is used.
-std=
Determine the language standard. This option is currently
only supported when compiling C or C++.
The compiler can accept several base standards, such as c90
or c++98, and GNU dialects of those standards, such as gnu90
or gnu++98. When a base standard is specified, the compiler
accepts all programs following that standard plus those using
GNU extensions that do not contradict it. For example,
-std=c90 turns off certain features of GCC that are
incompatible with ISO C90, such as the "asm" and "typeof"
keywords, but not other GNU extensions that do not have a
meaning in ISO C90, such as omitting the middle term of a
"?:" expression. On the other hand, when a GNU dialect of a
standard is specified, all features supported by the compiler
are enabled, even when those features change the meaning of
the base standard. As a result, some strict-conforming
programs may be rejected. The particular standard is used by
-Wpedantic to identify which features are GNU extensions
given that version of the standard. For example -std=gnu90
-Wpedantic warns about C++ style // comments, while
-std=gnu99 -Wpedantic does not.
A value for this option must be provided; possible values are
c90
c89
iso9899:1990
Support all ISO C90 programs (certain GNU extensions that
conflict with ISO C90 are disabled). Same as -ansi for C
code.
iso9899:199409
ISO C90 as modified in amendment 1.
c99
c9x
iso9899:1999
iso9899:199x
ISO C99. This standard is substantially completely
supported, modulo bugs and floating-point issues (mainly
but not entirely relating to optional C99 features from
Annexes F and G). See
<http://gcc.gnu.org/c99status.html > for more information.
The names c9x and iso9899:199x are deprecated.
c11
c1x
iso9899:2011
ISO C11, the 2011 revision of the ISO C standard. This
standard is substantially completely supported, modulo
bugs, floating-point issues (mainly but not entirely
relating to optional C11 features from Annexes F and G)
and the optional Annexes K (Bounds-checking interfaces)
and L (Analyzability). The name c1x is deprecated.
c17
c18
iso9899:2017
iso9899:2018
ISO C17, the 2017 revision of the ISO C standard
(published in 2018). This standard is same as C11 except
for corrections of defects (all of which are also applied
with -std=c11) and a new value of "__STDC_VERSION__", and
so is supported to the same extent as C11.
c2x The next version of the ISO C standard, still under
development. The support for this version is
experimental and incomplete.
gnu90
gnu89
GNU dialect of ISO C90 (including some C99 features).
gnu99
gnu9x
GNU dialect of ISO C99. The name gnu9x is deprecated.
gnu11
gnu1x
GNU dialect of ISO C11. The name gnu1x is deprecated.
gnu17
gnu18
GNU dialect of ISO C17. This is the default for C code.
gnu2x
The next version of the ISO C standard, still under
development, plus GNU extensions. The support for this
version is experimental and incomplete.
c++98
c++03
The 1998 ISO C++ standard plus the 2003 technical
corrigendum and some additional defect reports. Same as
-ansi for C++ code.
gnu++98
gnu++03
GNU dialect of -std=c++98.
c++11
c++0x
The 2011 ISO C++ standard plus amendments. The name
c++0x is deprecated.
gnu++11
gnu++0x
GNU dialect of -std=c++11. The name gnu++0x is
deprecated.
c++14
c++1y
The 2014 ISO C++ standard plus amendments. The name
c++1y is deprecated.
gnu++14
gnu++1y
GNU dialect of -std=c++14. This is the default for C++
code. The name gnu++1y is deprecated.
c++17
c++1z
The 2017 ISO C++ standard plus amendments. The name
c++1z is deprecated.
gnu++17
gnu++1z
GNU dialect of -std=c++17. The name gnu++1z is
deprecated.
c++2a
The next revision of the ISO C++ standard, tentatively
planned for 2020. Support is highly experimental, and
will almost certainly change in incompatible ways in
future releases.
gnu++2a
GNU dialect of -std=c++2a. Support is highly
experimental, and will almost certainly change in
incompatible ways in future releases.
-fgnu89-inline
The option -fgnu89-inline tells GCC to use the traditional
GNU semantics for "inline" functions when in C99 mode.
Using this option is roughly equivalent to adding the
"gnu_inline" function attribute to all inline functions.
The option -fno-gnu89-inline explicitly tells GCC to use the
C99 semantics for "inline" when in C99 or gnu99 mode (i.e.,
it specifies the default behavior). This option is not
supported in -std=c90 or -std=gnu90 mode.
The preprocessor macros "__GNUC_GNU_INLINE__" and
"__GNUC_STDC_INLINE__" may be used to check which semantics
are in effect for "inline" functions.
-fpermitted-flt-eval-methods=style
ISO/IEC TS 18661-3 defines new permissible values for
"FLT_EVAL_METHOD" that indicate that operations and constants
with a semantic type that is an interchange or extended
format should be evaluated to the precision and range of that
type. These new values are a superset of those permitted
under C99/C11, which does not specify the meaning of other
positive values of "FLT_EVAL_METHOD". As such, code
conforming to C11 may not have been written expecting the
possibility of the new values.
-fpermitted-flt-eval-methods specifies whether the compiler
should allow only the values of "FLT_EVAL_METHOD" specified
in C99/C11, or the extended set of values specified in
ISO/IEC TS 18661-3.
style is either "c11" or "ts-18661-3" as appropriate.
The default when in a standards compliant mode (-std=c11 or
similar) is -fpermitted-flt-eval-methods=c11. The default
when in a GNU dialect (-std=gnu11 or similar) is
-fpermitted-flt-eval-methods=ts-18661-3.
-aux-info filename
Output to the given filename prototyped declarations for all
functions declared and/or defined in a translation unit,
including those in header files. This option is silently
ignored in any language other than C.
Besides declarations, the file indicates, in comments, the
origin of each declaration (source file and line), whether
the declaration was implicit, prototyped or unprototyped (I,
N for new or O for old, respectively, in the first character
after the line number and the colon), and whether it came
from a declaration or a definition (C or F, respectively, in
the following character). In the case of function
definitions, a K&R-style list of arguments followed by their
declarations is also provided, inside comments, after the
declaration.
-fallow-parameterless-variadic-functions
Accept variadic functions without named parameters.
Although it is possible to define such a function, this is
not very useful as it is not possible to read the arguments.
This is only supported for C as this construct is allowed by
C++.
-fno-asm
Do not recognize "asm", "inline" or "typeof" as a keyword, so
that code can use these words as identifiers. You can use
the keywords "__asm__", "__inline__" and "__typeof__"
instead. -ansi implies -fno-asm.
In C++, this switch only affects the "typeof" keyword, since
"asm" and "inline" are standard keywords. You may want to
use the -fno-gnu-keywords flag instead, which has the same
effect. In C99 mode (-std=c99 or -std=gnu99), this switch
only affects the "asm" and "typeof" keywords, since "inline"
is a standard keyword in ISO C99.
-fno-builtin
-fno-builtin-function
Don't recognize built-in functions that do not begin with
__builtin_ as prefix.
GCC normally generates special code to handle certain built-
in functions more efficiently; for instance, calls to
"alloca" may become single instructions which adjust the
stack directly, and calls to "memcpy" may become inline copy
loops. The resulting code is often both smaller and faster,
but since the function calls no longer appear as such, you
cannot set a breakpoint on those calls, nor can you change
the behavior of the functions by linking with a different
library. In addition, when a function is recognized as a
built-in function, GCC may use information about that
function to warn about problems with calls to that function,
or to generate more efficient code, even if the resulting
code still contains calls to that function. For example,
warnings are given with -Wformat for bad calls to "printf"
when "printf" is built in and "strlen" is known not to modify
global memory.
With the -fno-builtin-function option only the built-in
function function is disabled. function must not begin with
__builtin_. If a function is named that is not built-in in
this version of GCC, this option is ignored. There is no
corresponding -fbuiltin-function option; if you wish to
enable built-in functions selectively when using -fno-builtin
or -ffreestanding, you may define macros such as:
#define abs(n) __builtin_abs ((n))
#define strcpy(d, s) __builtin_strcpy ((d), (s))
-fgimple
Enable parsing of function definitions marked with
"__GIMPLE". This is an experimental feature that allows unit
testing of GIMPLE passes.
-fhosted
Assert that compilation targets a hosted environment. This
implies -fbuiltin. A hosted environment is one in which the
entire standard library is available, and in which "main" has
a return type of "int". Examples are nearly everything
except a kernel. This is equivalent to -fno-freestanding.
-ffreestanding
Assert that compilation targets a freestanding environment.
This implies -fno-builtin. A freestanding environment is one
in which the standard library may not exist, and program
startup may not necessarily be at "main". The most obvious
example is an OS kernel. This is equivalent to -fno-hosted.
-fopenacc
Enable handling of OpenACC directives "#pragma acc" in C/C++
and "!$acc" in Fortran. When -fopenacc is specified, the
compiler generates accelerated code according to the OpenACC
Application Programming Interface v2.0
<https://www.openacc.org >. This option implies -pthread, and
thus is only supported on targets that have support for
-pthread.
-fopenacc-dim=geom
Specify default compute dimensions for parallel offload
regions that do not explicitly specify. The geom value is a
triple of ':'-separated sizes, in order 'gang', 'worker' and,
'vector'. A size can be omitted, to use a target-specific
default value.
-fopenmp
Enable handling of OpenMP directives "#pragma omp" in C/C++
and "!$omp" in Fortran. When -fopenmp is specified, the
compiler generates parallel code according to the OpenMP
Application Program Interface v4.5 <https://www.openmp.org >.
This option implies -pthread, and thus is only supported on
targets that have support for -pthread. -fopenmp implies
-fopenmp-simd.
-fopenmp-simd
Enable handling of OpenMP's SIMD directives with "#pragma
omp" in C/C++ and "!$omp" in Fortran. Other OpenMP directives
are ignored.
-fgnu-tm
When the option -fgnu-tm is specified, the compiler generates
code for the Linux variant of Intel's current Transactional
Memory ABI specification document (Revision 1.1, May 6 2009).
This is an experimental feature whose interface may change in
future versions of GCC, as the official specification
changes. Please note that not all architectures are
supported for this feature.
For more information on GCC's support for transactional
memory,
Note that the transactional memory feature is not supported
with non-call exceptions (-fnon-call-exceptions).
-fms-extensions
Accept some non-standard constructs used in Microsoft header
files.
In C++ code, this allows member names in structures to be
similar to previous types declarations.
typedef int UOW;
struct ABC {
UOW UOW;
};
Some cases of unnamed fields in structures and unions are
only accepted with this option.
Note that this option is off for all targets but x86 targets
using ms-abi.
-fplan9-extensions
Accept some non-standard constructs used in Plan 9 code.
This enables -fms-extensions, permits passing pointers to
structures with anonymous fields to functions that expect
pointers to elements of the type of the field, and permits
referring to anonymous fields declared using a typedef.
This is only supported for C, not C++.
-fcond-mismatch
Allow conditional expressions with mismatched types in the
second and third arguments. The value of such an expression
is void. This option is not supported for C++.
-flax-vector-conversions
Allow implicit conversions between vectors with differing
numbers of elements and/or incompatible element types. This
option should not be used for new code.
-funsigned-char
Let the type "char" be unsigned, like "unsigned char".
Each kind of machine has a default for what "char" should be.
It is either like "unsigned char" by default or like "signed
char" by default.
Ideally, a portable program should always use "signed char"
or "unsigned char" when it depends on the signedness of an
object. But many programs have been written to use plain
"char" and expect it to be signed, or expect it to be
unsigned, depending on the machines they were written for.
This option, and its inverse, let you make such a program
work with the opposite default.
The type "char" is always a distinct type from each of
"signed char" or "unsigned char", even though its behavior is
always just like one of those two.
-fsigned-char
Let the type "char" be signed, like "signed char".
Note that this is equivalent to -fno-unsigned-char, which is
the negative form of -funsigned-char. Likewise, the option
-fno-signed-char is equivalent to -funsigned-char.
-fsigned-bitfields
-funsigned-bitfields
-fno-signed-bitfields
-fno-unsigned-bitfields
These options control whether a bit-field is signed or
unsigned, when the declaration does not use either "signed"
or "unsigned". By default, such a bit-field is signed,
because this is consistent: the basic integer types such as
"int" are signed types.
-fsso-struct=endianness
Set the default scalar storage order of structures and unions
to the specified endianness. The accepted values are big-
endian, little-endian and native for the native endianness of
the target (the default). This option is not supported for
C++.
Warning: the -fsso-struct switch causes GCC to generate code
that is not binary compatible with code generated without it
if the specified endianness is not the native endianness of
the target.
