将C/C++程序转换为预处理器代码

g++ -E program.cpp

<span class="com">#define</span><span class="pln"> PI </span><span class="lit">3.1415</span>
<span class="kwd">int</span><span class="pln"> main</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span>
<span class="kwd">   float</span><span class="pln"> a </span><span class="pun">=</span><span class="pln"> PI</span><span class="pun">,</span><span class="pln"> r </span><span class="pun">=</span><span class="pln"> </span><span class="lit">5</span><span class="pun">;</span>
<span class="kwd">   float</span><span class="pln"> c </span><span class="pun">=</span><span class="pln"> a </span><span class="pun">*</span><span class="pln"> r </span><span class="pun">*</span><span class="pln"> r</span><span class="pun">;</span>
<span class="kwd">   return</span><span class="pln"> </span><span class="lit">0</span><span class="pun">;</span>
<span class="pun">}</span>

$ g++ -E test_prog.cpp
int main() {
   float a = 3.1415, r = 5;
   float c = a * r * r;
   return 0;
}