📄 typedefconst2.html
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<html><!-- <2004May05.2345.scs.009@scs.ndip.eskimo.net> --><!-- Mirrored from c-faq.com/ansi/typedefconst2.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 08:02:58 GMT --><head><title></title></head><body><p>[This is]another of the differences between <TT>typedef</TT> and <TT>#define</TT>.<p>Type qualifiers like <TT>const</TT> can affect a pointer variable in two(or more) different ways: either the pointer can be qualified, orthe value pointed to. As <a href="constptrconst.html">question 11.9</a> in the C FAQ list explains,when you write<pre> int * const p;</pre>the pointer <TT>p</TT> is qualified, but when you write<pre> const int * p;</pre>the value pointed to is qualified.<p>Now, if you say<pre> #define x int*</pre>and then<pre> const x y;</pre>the result is exactly as if you had written<pre> const int* y;</pre>so it is the pointed-to value that is qualified. Thepreprocessor always does simple textual substitutions, and thesetake place before the compiler performs its parsing phase.<p>When you say<pre> typedef int * x;</pre>on the other hand, <TT>x</TT> is a new type, encapsulating the notion“pointer to <TT>int</TT>”. Now, when you say<pre> const x y;</pre>it is the variable <TT>y</TT> that is qualified, just as if you'd said<pre> const int y;</pre></body><!-- Mirrored from c-faq.com/ansi/typedefconst2.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 08:02:58 GMT --></html>⌨️ 快捷键说明
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