静态const与#define在C ++中-可执行文件大小的差异 [英] static const vs. #define in c++ - differences in executable size

问题描述

我的基本情况：我有一个包含文件，其内容类似于 #define foo（Flag1 | Flags2 | Flag3），因此它是位标志的预定义组合。为了确保类型安全，我想将这些#defines替换为静态const，即 static const int foo =（Flag1 | Flag2 | Flag3）（或类似名称）。该包含文件包含在程序的数十个位置中。

My basic situation: I have an include file that has something like #define foo (Flag1 | Flags2 | Flag3), so it's a predefined combination of bit flags. For the sake of type-safety, I wanted to replace these #defines by static consts, i.e. static const int foo = (Flag1 | Flag2 | Flag3) (or similar). This include file is included in dozens of places in the program.

现在，当我在发布版本中启用了所有相关的优化选项时（使用VS2010的C ++编译器） ），替换#defines似乎会使可执行文件增加几KiB，具体取决于我替换了多少个常量。

Now when I'm doing a release build with all relevant optimisation options enabled (using the C++ compiler of VS2010), replacing the #defines seems to increase the executable by a few KiB, depending on how many constants I replaced.

为什么会这样？据我所知，如果可能的话，应该将整数常量内联到生成的ASM代码中，而且我看不到如何使用 static const vs #define 在这里会有所作为。显然，反汇编显示该变量不是内联的：

Why does this happen? To my knowledge, integer constants are supposed to be "inlined" into the ASM code that is produced if possible, and I don't see how using a static const vs #define would make a difference here. Clearly, the variable isn't inlined as the disassembly shows:

#define:
01325041  or          eax,0FFD87FE0h
static int:
011E5451  or          eax,dword ptr [CMainFrame::s_TemplateModulePaths+38h (151F008h)]

最后一个问题是：如何避免 #define 但仍然依赖于直接将变量插入到生成的程序集中？

So the final question is: How can I avoid #define but still rely on the variable being inserted directly into the generated assembly?

推荐答案

如注释所示，类型安全运算符|我的枚举的重载似乎阻止VC ++内联ORed值。我想我会继续使用 #define 版本，因为我讨厌在没有好处的情况下增加可执行文件的大小（不，这不是过早的优化）-毕竟，它没有不会增加可读性，并且由于标记的组合已经是我的flagset枚举类型，我想我也不会失去任何类型安全性。

As seen in the comments, the typesafe operator| overloading for my enums seems to prevent VC++ from inlining the ORed value. I guess I'll keep using the #define version as I hate increasing the executable size if there's no benefits (no, this is not premature optimization) - after all, it doesn't increase readability, and since the combination of flags is already of my flagset enum type, I also don't lose any type-safety, I guess.

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