宏扩展 [英] Macro Expansion

问题描述

基本问题

#define A 5
#define B 10

#define C (A*B)


int var;
var = C;

所以这里宏将如何扩大，是不是

so here how macros will be expanded, Is it

var = (5*10)

或

var = (50)

我的怀疑是对宏扩展。如果宏有一定的计算 - 在所有常数（*，/，+），然后将马可只是在网上膨胀或将评估结果，并张贴

My doubt is on the macro expansion. If macros has some calculations (*,-,/,+) on all constant,then will marco is just a in line expansion or it will evaluate the result and post it

推荐答案

宏扩展是永远只是一个文本转换输入源$ C ​​$ C的。你应该能够看到code中的pre处理器（即不宏扩展汇编的一部分）完成后，本文是编译器正确，然后对工作

Macro expansion is always just a textual transform of the input source code. You should be able to see the code after the pre-processor (the part of the compilation that does the macro expansion) is done; this text is what the compiler proper then works on.

但是，许多编译器做在编译过程中常量折叠的优化，这将优化 5 * 10 到 50 等等它并不需要在运行时计算。

But many compilers do "constant folding" optimization during compilation, that will optimize 5 * 10 to 50 so that it doesn't need to be calculated at runtime.

这篇关于宏扩展的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！