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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><HTML><HEAD> <META NAME="GENERATOR" CONTENT="LinuxDoc-Tools 0.9.20"> <TITLE>cc65 Users Guide: Extensions</TITLE> <LINK HREF="cc65-6.html" REL=next> <LINK HREF="cc65-4.html" REL=previous> <LINK HREF="cc65.html#toc5" REL=contents></HEAD><BODY><A HREF="cc65-6.html">Next</A><A HREF="cc65-4.html">Previous</A><A HREF="cc65.html#toc5">Contents</A><HR><H2><A NAME="s5">5.</A> <A HREF="cc65.html#toc5">Extensions</A></H2><P>This cc65 version has some extensions to the ISO C standard.</P><P><UL><LI> The compiler allows // comments (like in C++ and in the proposed C9xstandard). This feature is disabled by <CODE><A HREF="cc65-2.html#option-A">-A</A></CODE>.</LI><LI> The compiler allows to insert assembler statements into the outputfile. The syntax is<BLOCKQUOTE><CODE><PRE> asm (<string literal>[, optional parameters]) ; </PRE></CODE></BLOCKQUOTE>or<BLOCKQUOTE><CODE><PRE> __asm__ (<string literal>[, optional parameters]) ; </PRE></CODE></BLOCKQUOTE>The first form is in the user namespace and is disabled if the <CODE>-A</CODE>switch is given.There is a whole section covering inline assembler statements,<A HREF="cc65-9.html#inline-asm">see there</A>.</LI><LI> There is a special calling convention named "fastcall". This callingconvention is currently only usable for functions written inassembler. The syntax for a function declaration using fastcall is<BLOCKQUOTE><CODE><PRE> <return type> fastcall <function name> (<parameter list>) </PRE></CODE></BLOCKQUOTE>or<BLOCKQUOTE><CODE><PRE> <return type> __fastcall__ <function name> (<parameter list>) </PRE></CODE></BLOCKQUOTE>An example would be<BLOCKQUOTE><CODE><PRE> void __fastcall__ f (unsigned char c) </PRE></CODE></BLOCKQUOTE>The first form of the fastcall keyword is in the user namespace and istherefore disabled in strict ANSI mode.For functions declared as <CODE>fastcall</CODE>, the rightmost parameter is notpushed on the stack but left in the primary register when the functionis called. This will reduce the cost when calling assembler functionssignificantly, especially when the function itself is rather small.</LI><LI> There are two pseudo variables named <CODE>__AX__</CODE> and <CODE>__EAX__</CODE>.Both refer to the primary register that is used by the compiler toevaluate expressions or return function results. <CODE>__AX__</CODE> is oftype <CODE>unsigned int</CODE> and <CODE>__EAX__</CODE> of type <CODE>long unsigned int</CODE>respectively. The pseudo variables may be used as lvalue and rvalue asevery other variable. They are most useful together with shortsequences of assembler code. For example, the macro<BLOCKQUOTE><CODE><PRE> #define hi(x) (__AX__=(x),asm("\ttxa\n\tldx\t#$00",__AX__) </PRE></CODE></BLOCKQUOTE>will give the high byte of any unsigned value.</LI><LI> Inside a function, the identifier <CODE>__func__</CODE> gives the name of thecurrent function as a string. Outside of functions, <CODE>__func__</CODE> isundefined.Example:<BLOCKQUOTE><CODE><PRE> #define PRINT_DEBUG(s) printf ("%s: %s\n", __func__, s); </PRE></CODE></BLOCKQUOTE>The macro will print the name of the current function plus a givenstring.</LI><LI> cc65 allows the initialization of <CODE>void</CODE> variables. This may beused to create variable structures that are more compatible withinterfaces written for assembler languages. Here is an example:<BLOCKQUOTE><CODE><PRE> void GCmd = { (char)3, (unsigned)0x2000, (unsigned)0x3000 }; </PRE></CODE></BLOCKQUOTE>This will be translated as follows:<BLOCKQUOTE><CODE><PRE> _GCmd: .byte 3 .word $2000 .word $3000 </PRE></CODE></BLOCKQUOTE>Since the variable is of type <CODE>void</CODE> you may not use it as is.However, taking the address of the variable results in a <CODE>void*</CODE>which may be passed to any function expecting a pointer.See the <A HREF="geos.html">GEOS library</A> for examples onhow to use this feature.</LI><LI> cc65 implements flexible array struct members as defined in the C99 ISOstandard. As an extension, in non ANSI mode, these fields may beinitialized. There are several exceptions, however (which is probablythe reason why the standard does not define this feature, because it ishighly unorthogonal). Flexible array members cannot be initialized...<UL><LI> ...when defining an array of structs with flexible members.</LI><LI> ...if such a struct is a member field of another struct whichis not the last field.</LI><LI> If the struct which contains a flexible array member isdeclared as <CODE>register</CODE> and the size and compiler settingsdo allow the compiler to actually place the struct into theregister bank in the zero page.</LI></UL>Please note that - as defined in the ISO C standard - the <CODE>sizeof</CODE>operator returns the struct size with the flexible array member havingsize zero, even if it is initialized.</LI></UL></P><HR><A HREF="cc65-6.html">Next</A><A HREF="cc65-4.html">Previous</A><A HREF="cc65.html#toc5">Contents</A></BODY></HTML>⌨️ 快捷键说明
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