尾递归没有发生 [英] Tail-recursion not happening

问题描述

我在C ++项目中使用 g ++（Ubuntu 4.8.2-19ubuntu1）4.8.2 。我写了一个这样的函数：

I'm using g++ (Ubuntu 4.8.2-19ubuntu1) 4.8.2 in a C++ project. I wrote a function that kind of does this:

template<typename T, T (*funct)(int) >
multiset<T> Foo(const multiset<T>& bar, int iterations) {
    if (iterations == 0) return bar; 
    multiset<T> copy_bar(bar); 

    T baz = funct(copy_bar.size());

    if (baz.attr > 0)
        return Foo<T,funct>(copy_bar, 100);
    else 
        return Foo<T,funct>(bar, iterations - 1);    
}

我得到 bad_alloc（）exception ，所以我用 gdb 测试了函数，结果发现没有尾递归发生，这是我期待的，因为<$ c $之后没有语句c> return s。

I was getting bad_alloc() exception so I tested the function with gdb and turns out that there's no tail-recursion happening, which I was expecting since there are no statements after the returns.

注意：我尝试使用-O2编译标志，但它不起作用

NOTE: I tried with -O2 compilation flag but it didn't work

推荐答案

你的函数是不是尾递归，因为递归调用之后仍有工作要做：销毁 copy_bar （它有一个非平凡的析构函数），也可能是 baz （如果类型 T 也有一个非平凡的析构函数）。

Your function is not tail-recursive, since there's still work to do after the recursive call: Destruction of copy_bar (which has a non-trivial destructor) and possibly also of baz (if the type T also has a non-trivial destructor).

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