0c, 1c, 2c, 5c, 6c, 7c, 8c, kc, qc, vc – C compilers


2c [ option ... ] [ file ... ]


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 compilations 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


qc power

Power PC  

vc mips

big-endian MIPS 3000 family  

The compilers handle most preprocessing directives themselves; 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 appropriate to the current machine’s type. Plan 9 also conventionally 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).

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.  


Print warning messages about unused variables, etc.  


Accept functions without a new-style ANSI C function prototype. By default, the compilers reject functions used without a defined prototype, although ANSI C permits them.  



unhandled troff command .ns


Define the name to the preprocessor, as if by #define. If no definition is given, the name is defined as 1.  


Enable type-checking of calls to print(2) and other formatted print routines. See the discussion of extensions, below.  


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.  


Suppress automatic registerization and optimization.  


Print an assembly language version of the object code on standard output as well as generating the .O file.  


Pass type signatures on all external and global entities. The signature is based on the C signof operator.  


By default, the compilers are non-standardly lax about type equality between void* values and other pointers; this flag requires ANSI C conformance.  


Invoke a standard ANSI C preprocessor before compiling.  


Instead of compiling, print on standard output acid functions (see acid(1)) for examining structures declared in the source files.  


Like -a except suppress information about structures declared in included header files.  


When used with -a or -aa, places acid functions in file.acid for input file.c, and not on standard output.  

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 structure 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 /$objtype/lib/libbio.a; such lines, typically placed in library header files, obviate the -l option of the loaders. To help identify files in non-standard directories, within the file names in the #pragmas the string $M represents 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 compiler that the corresponding type should have its signature calculated as an incomplete type even if it is subsequently 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

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.  


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



system area for machine-independent #include directives.  


system area for machine-dependent #include directives.  



machine-independent part  

/sys/src/cmd/2c, etc.

machine-dependent part  


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”


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 implemented.

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).