.TH TYPES 2.SH NAMEtypes \- c type system.SH SYNOPSIS.BR char , .BR short ,.BR int , .BR vlong.PP.BR uchar ,.BR ushort ,.BR uint ,.BR uvlong.PP.BR u8int ,.BR u16int ,.BR u32int ,.BR u64int.PP.B Rune.PP.BR usize ,.BR uintptr.PP.B uintmem.PP.B schar.SH DESCRIPTIONThe Plan 9 C compilers and system use a specialization of the C99 type system,which has evolved over time.The compilers are unsigned preserving, and.B charcan be assumed to be a signed value.Although the system currently makes heavy use of.BR ulong to represent exactly-32-bit integers and pointers as unsignedintegers, this practice is no longer supportable with the advent oftrue 64-bit compilers.  Having a more explicit type set permits us tobe more specific about intent and is helpful to maintain portabilityto other systems, especially Plan 9 from User Space..PPThe basic 8, 16, 32 and 64-bit types are.BR char ,.BR short ,.BR int ,and.BR vlong.Conventionally, unsigned types simply prepend a "u" to the basic type name ratherthan using the.B unsignedprefix..PPMost programs will need no more integer types than this.  Exceptionscome in two forms: the need to be specific about use to aid inporting, and type widths fixed by hardware or protcols.The system call interface does not fit the second case since the compileritself will pick the same sizes for both kernel and user space..PPTo specify an integer of a particular width, the form.BI u bits intis used.  Types for 8, 16, 32, and 64 bit-width specific unsignedintegers are available.  There are no signed variants of these as theyare not useful where size-specific types are appropriate.  As aspecial case,.B ucharis assumed to be equivalent to.BR u8int .Beware of using size-specific integers in a structure as a marshallingtechnique.  The compiler is free to pad the structure and endianconversion can easily be forgotten.  Consider using a structureof basic types (typically uchar) marshalled with functions as in.IR getbe (2)..PPThe.B Runetype stands alone.  It holds a single unicode codepoint asdescribed in.IR rune (2)and.IR utf (6)..PPThe use-specific types are.B usizeand.BR uintptr ..B Usizerepresents the type returned by the C.B sizeofoperator.  It is typically the same width as a virtual address.In order to ease the transition to 64-bits, the AMD64 compilercurrently uses a 32-bit.BR usize .An integer representation of a virtual-address pointer is represented by the type.BR uintptr ..PPThe kernel additionally needs to specify a type to represent aphysical address. Since physical addresses may be the same size,larger (PAE) or smaller than virtual addresses,.B uintmemas a physical address may be the same size, larger (PAE), or smaller than a virtual address..B Uintmemalso stores the sizes of things that.B uintmemmight address..PPFinally,.B scharis used when porting to other systems where it may matter.  It should not generally be used..SH EXAMPLESThe C library has a number of functions which are in needof conversion.  For example,.IP.EXvoid*	malloc(usize nbytes);int		segfree(void *va, usize len);uintptr	getcallerpc(void*);.EE.PPA device driver might access a 32-bit register with.IP.EXu32int regval; regval = regbase[regoff/4];.EE.PPIn the kernel we could convert between physical and virtual addressesthis way:.IP.EXuintmem	upaddr(uintptr kva);uintptr	upaddr(uintmem pa);.EE.PPThe actual functions use.B void*for kernel addresses..SH "SEE ALSO".IR 8c (1),.IR getbe (2),.IR rune (2),.IR utf (6),.brPlan 9 from User Space,.B http://swtch.com/plan9port.SH BUGSThe spirit of the original type system has faded with time.