📄 rawmemadr.html
字号:
<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN"><!-- This collection of hypertext pages is Copyright 1995-2005 by Steve Summit. --><!-- Content from the book "C Programming FAQs: Frequently Asked Questions" --><!-- (Addison-Wesley, 1995, ISBN 0-201-84519-9) is made available here by --><!-- permission of the author and the publisher as a service to the community. --><!-- It is intended to complement the use of the published text --><!-- and is protected by international copyright laws. --><!-- The on-line content may be accessed freely for personal use --><!-- but may not be published or retransmitted without explicit permission. --><!-- --><!-- this page built Sat Dec 24 21:47:47 2005 by faqproc version 2.7 --><!-- from source file osdepmem.sgml dated Sat Feb 14 21:25:34 2004 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/osdep/rawmemadr.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:59:03 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 19.25</title><link href="dgroup.html" rev=precedes><link href="endiantest.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="dgroup.html" rev=precedes><img src="../images/buttonleft.gif" alt="prev"></a><a href="index.html" rev=subdocument><img src="../images/buttonup.gif" alt="up"></a><a href="endiantest.html" rel=precedes><img src="../images/buttonright.gif" alt="next"></a> <a href="../index-2.html"><img src="../images/buttontop.gif" alt="top/contents"></a><a href="../search.html"><img src="../images/buttonsrch.gif" alt="search"></a><hr><p><!-- qbegin --><h1>comp.lang.c FAQ list<font color=blue>·</font><!-- qtag -->Question 19.25</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>How can I access memory(a memory-mapped device,or graphics memory)located at a certain address?<br>How can I do PEEK and POKE in C?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Set a pointer,of the appropriate type,to the right number(using an explicit castto assure the compilerthat you really do intend this nonportable conversion):<pre> unsigned int *magicloc = (unsigned int *)0x12345678;</pre>Then, <TT>*magicloc</TT> refers to the location you want.<a href="fn92.html" rel=subdocument>[footnote]</a>If the location is a memory-mapped I/O register,you will probably also want to usethe <TT>volatile</TT> qualifier:``<TT>volatile unsigned int *magicloc</TT>''.(If you want to refer to a byte at a certain addressrather than a word,use <TT>unsigned char *</TT>.)</p><p>UnderMS-DOS,you may find a macro like <TT>MK_FP()</TT>handyfor working with segments andoffsets.As suggested by Gary Blaine,you can also declare tricky array pointers which allow you to access screen memory using arraynotation.For example,on an MS-DOS machinein an 80x25 text mode,given the declaration<pre>unsigned short (far * videomem)[80] = (unsigned short (far *)[80])0xb8000000;</pre>you can access the character and attribute byteat row <TT>i</TT>, column <TT>j</TT>with <TT>videomem[i][j]</TT>.</p><p>Manyoperating systems execute user-mode programsin a protected modewhere direct access to I/O devices(or to <em>any</em> address outside the running process)is simply not possible.In such cases youwillhave to ask the operating systemto carry out I/O operations for you.</p><p>See also questions<a href="../ptrs/int2ptr.html">4.14</a>and<a href="../null/accessloc0.html">5.19</a>.</p><p>References:K&R1 Sec. A14.4 p. 210<br>K&R2 Sec. A6.6 p. 199<br>ISO Sec. 6.3.4<br>Rationale Sec. 3.3.4<br>H&S Sec. 6.2.7 pp. 171-2<br></p><!-- aend --><p><hr><a href="dgroup.html" rev=precedes><img src="../images/buttonleft.gif" alt="prev"></a><a href="index.html" rev=subdocument><img src="../images/buttonup.gif" alt="up"></a><a href="endiantest.html" rel=precedes><img src="../images/buttonright.gif" alt="next"></a> <a href="../questions.html"><img src="../images/buttontop.gif" alt="contents"></a><a href="../search.html"><img src="../images/buttonsrch.gif" alt="search"></a><br><!-- lastfooter --><a href="../about.html">about this FAQ list</a> <a href="../eskimo.html">about eskimo</a> <a href="../search.html">search</a> <a href="../feedback.html">feedback</a> <a href="copyright.html">copyright</a><p>Hosted by<a href="http://www.eskimo.com/"><img src="../../www.eskimo.com/img/link/eskitiny.gif" alt="Eskimo North"></a></body><!-- Mirrored from c-faq.com/osdep/rawmemadr.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:59:03 GMT --></html>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -