問題描述

我讀到使用 C++ 異常進(jìn)行異常處理有一些開銷，而不是檢查返回值.我只是在談?wù)摏]有拋出異常時(shí)產(chǎn)生的開銷.我還假設(shè)您需要實(shí)現(xiàn)實(shí)際檢查返回值并執(zhí)行適當(dāng)操作的代碼，無論與 catch 塊所做的操作等效.而且，將拋出異常對象的代碼與其中包含 45 個(gè)狀態(tài)變量的代碼進(jìn)行比較，并為每個(gè)錯(cuò)誤返回一個(gè)負(fù)整數(shù)的代碼也是不公平的.

I have read that there is some overhead to using C++ exceptions for exception handling as opposed to, say, checking return values. I'm only talking about overhead that is incurred when no exception is thrown. I'm also assuming that you would need to implement the code that actually checks the return value and does the appropriate thing, whatever would be the equivalent to what the catch block would have done. And, it's also not fair to compare code that throws exception objects with 45 state variables inside to code that returns a negative integer for every error.

我不是試圖僅僅基于哪個(gè)可能執(zhí)行得更快來構(gòu)建支持或反對 C++ 異常的案例.我聽說最近有人提出這樣的案例，一旦您考慮到檢查返回值和處理錯(cuò)誤所需的所有額外簿記代碼，使用異常的代碼應(yīng)該與基于返回代碼的代碼一樣快地運(yùn)行.我錯(cuò)過了什么?

I'm not trying to build a case for or against C++ exceptions solely based on which one might execute faster. I heard someone make the case recently that code using exceptions ought to run just as fast as code based on return codes, once you take into account all the extra bookkeeping code that would be needed to check the return values and handle the errors. What am I missing?

推薦答案

某些 平臺(tái)和某些 編譯器上的異常處理會(huì)產(chǎn)生相關(guān)成本.

There is a cost associated with exception handling on some platforms and with some compilers.

也就是說，Visual Studio 在構(gòu)建 32 位目標(biāo)時(shí)，將在每個(gè)具有非平凡析構(gòu)函數(shù)的局部變量的函數(shù)中注冊一個(gè)處理程序.基本上，它設(shè)置了一個(gè) try/finally 處理程序.

Namely, Visual Studio, when building a 32-bit target, will register a handler in every function that has local variables with non-trivial destructor. Basically, it sets up a try/finally handler.

gcc 和面向 64 位的 Visual Studio 采用的另一種技術(shù)僅在拋出異常時(shí)產(chǎn)生開銷(該技術(shù)涉及遍歷調(diào)用堆棧和表抬頭).在很少拋出異常的情況下，這實(shí)際上可以產(chǎn)生更高效的代碼，因?yàn)椴槐靥幚礤e(cuò)誤代碼.

The other technique, employed by gcc and Visual Studio targeting 64-bits, only incurs overhead when an exception is thrown (the technique involves traversing the call stack and table lookup). In cases where exceptions are rarely thrown, this can actually lead to a more efficient code, as error codes don't have to be processed.

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