2C(1) 2C(1)
NAME
0c, 1c, 2c, 5c, 6c, 7c, 8c, kc, qc, vc - C compilers
SYNOPSIS
2c [ option ... ] [ file ... ]
etc.
DESCRIPTION
These commands compile the named C files into object files
for the corresponding architecture. If there are multiple C
files, the compilers will attempt to keep $NPROC compila-
tions running concurrently. Associated with each compiler
is a string objtype, for example
0c spim little-endian MIPS 3000 family
1c 68000 Motorola MC68000
2c 68020 Motorola MC68020
5c arm little-endian ARM
6c amd64 AMD64 and compatibles (e.g., Intel EM64T)
7c arm64 ARM64 (ARMv8)
8c 386 Intel i386, i486, Pentium, etc.
kc sparc Sun SPARC
qc power Power PC
vc mips big-endian MIPS 3000 family
The compilers handle most preprocessing directives them-
selves; a complete preprocessor is available in cpp(1),
which must be run separately.
Let the first letter of the compiler name be O= 0, 1, 2, 5,
6, 7, 8, k, q, or v. The output object files end in .O.
The letter is also the prefix of related programs: Oa is the
assembler, Ol is the loader. Plan 9 conventionally sets the
$objtype environment variable to the objtype string appro-
priate to the current machine's type. Plan 9 also conven-
tionally has /objtype directories, which contain among other
things: include, for machine-dependent include files; lib,
for public object code libraries; bin, for public programs;
and mkfile, for preconditioning mk(1).
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2C(1) 2C(1)
The compiler options are:
-o obj Place output in file obj (allowed only if there is
just one input file). Default is to take the last
element of the input file name, strip any trailing
.c, and append .O.
-w Print warning messages about unused variables, etc.
-B Accept functions without a new-style ANSI C function
prototype. By default, the compilers reject func-
tions used without a defined prototype, although ANSI
C permits them.
-Dname=def
-Dname Define the name to the preprocessor, as if by
`#define'. If no definition is given, the name is
defined as `1'.
-F Enable type-checking of calls to print(2) and other
formatted print routines. See the discussion of
extensions, below.
-Idir An `#include' file whose name does not begin with
slash or is enclosed in double quotes is always
sought first in the directory of the file argument.
If this fails, the -. flag is given or the name is
enclosed in <>, it is then sought in directories
named in -I options, then in /sys/include, and
finally in /$objtype/include.
-. Suppress the automatic searching for include files in
the directory of the file argument.
-N Suppress automatic registerization and optimization.
-S Print an assembly language version of the object code
on standard output as well as generating the .O file.
-T Pass type signatures on all external and global enti-
ties. The signature is based on the C signof opera-
tor.
-V By default, the compilers are non-standardly lax
about type equality between void* values and other
pointers; this flag requires ANSI C conformance.
-p Invoke a standard ANSI C preprocessor before compil-
ing.
-a Instead of compiling, print on standard output acid
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2C(1) 2C(1)
functions (see acid(1)) for examining structures
declared in the source files.
-aa Like -a except suppress information about structures
declared in included header files.
-n When used with -a or -aa, places acid functions in
file.acid for input file.c, and not on standard out-
put.
The compilers support several extensions to ANSI C:
- A structure or union may contain unnamed substructures and
subunions. The fields of the substructures or subunions
can then be used as if they were members of the parent
structure or union (the resolution of a name conflict is
unspecified). When a pointer to the outer structure or
union is used in a context that is only legal for the
unnamed substructure, the compiler promotes the type and
adjusts the pointer value to point at the substructure.
If the unnamed structure or union is of a type with a tag
name specified by a typedef statement, the unnamed struc-
ture or union can be explicitly referenced by <struct
variable>.<tagname>.
- A structure value can be formed with an expression such as
(struct S){v1, v2, v3}
where the list elements are values for the fields of
struct S.
- Array initializers can specify the indices of the array in
square brackets, as
int a[] = { [3] 1, [10] 5 };
which initializes the third and tenth elements of the
eleven-element array a.
- Structure initializers can specify the structure element
by using the name following a period, as
struct { int x; int y; } s = { .y 1, .x 5 };
which initializes elements y and then x of the structure
s. These forms also accept the new ANSI C notation, which
includes an equal sign:
int a[] = { [3] = 1, [10] = 5 };
struct { int x; int y; } s = { .y = 1, .x = 5 };
- A global variable can be dedicated to a register by
declaring it extern register in all modules and libraries.
- A #pragma of the form
#pragma lib "libbio.a"
records that the program needs to be loaded with file
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/$objtype/lib/libbio.a; such lines, typically placed in
library header files, obviate the -l option of the load-
ers. To help identify files in non-standard directories,
within the file names in the #pragmas the string $M repre-
sents the name of the architecture (e.g., mips) and $O
represents its identifying character (e.g., v).
- A #pragma of the form
#pragma varargck argpos error 2
tells the compiler that the second argument to error is a
print-like format string (see print(2)) that identifies
the handling of subsequent arguments. The #pragma
#pragma varargck type "s" char*
says that the format verb s processes an argument of type
char*. The #pragma
#pragma varargck flag 'c'
says that c is a flag character. These #pragmas are used,
if the -F option is enabled, to type-check calls to print
and other such routines.
- A #pragma with any of the following forms:
#pragma incomplete type
#pragma incomplete struct tag
#pragma incomplete union tag
where type is a typedef'd name for a structure or union
type, and tag is a structure or union tag, tells the com-
piler that the corresponding type should have its signa-
ture calculated as an incomplete type even if it is subse-
quently fully defined. This allows the type signature
mechanism to work in the presence of opaque types declared
in header files, with their full definitions visible only
to the code which manipulates them. With some imported
software it might be necessary to turn off the signature
generation completely for a large body of code (typically
at the start and end of a particular include file). If
type is the word _off_, signature generation is turned
off; if type is the word _on_, the compiler will generate
signatures.
- The C++ comment (// to end of line) is accepted as well as
the normal convention of /* */.
- The compilers accept long long variables as a 64-bit type.
The standard header typedefs this to vlong. Arithmetic on
vlong values is usually emulated by a run-time library,
though in at least 8c, only division and modulus use the
run-time library and the other operators generate in-line
code (and uvlong-expression division-or-modulus
(1<<constant) will turn into in-line bit operations, as is
done for shorter unsigned expressions).
Other differences with ANSI C include
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- The compilers use the original "unsigned preserving",
rather than ANSI C "value preserving" rules, which means
that, e.g., unsigned char gets promoted to unsigned int
rather than int.
- Parameters in macros are substituted inside of strings.
EXAMPLE
For the 68020, produce a program prog from C files main.c
and sub.c:
2c -FVw main.c sub.c
2l -o prog main.2 sub.2
FILES
/sys/include system area for machine-independent
#include directives.
/$objtype/include system area for machine-dependent
#include directives.
SOURCE
/sys/src/cmd/cc machine-independent part
/sys/src/cmd/2c, etc. machine-dependent part
SEE ALSO
2a(1), 2l(1), cpp(1), mk(1), nm(1), pcc(1), db(1), acid(1)
Rob Pike, ``How to Use the Plan 9 C Compiler''
BUGS
The list of compilers given above is only partial, not all
architectures are supported on all systems, some have been
retired and some are provided by third parties.
The default preprocessor only handles `#define', `#include',
`#undef', `#ifdef', `#line', and `#ifndef'. For a full ANSI
preprocessor, use the p option.
The default search order for include files differs to that
of cpp(1).
Some features of C99, the 1999 ANSI C standard, are imple-
mented.
switch expressions may not be either signedness of vlong on
32-bit architectures (8c at least).
The implementation of vlong assignment can use a static
location and this can be disturbed by interrupts (e.g.,
notes) (8c at least).
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