What are the conditions for tail recursion optimization of C++ functions?

The conditions for tail recursive optimization (TCO) in C are as follows: the tail recursive call must be the last action of the function. A function's parameters and local variables must remain unchanged across tail-recursive calls. The compiler must support TCO. In a practical case, TCO is used to convert the tail recursive call of the factorial calculation function into a while loop, which improves performance.

Conditions for tail recursive optimization of C functions

Tail recursive optimization (TCO) is a compiler optimization technology that will Tail-recursive function calls are converted into jump instructions, thus avoiding the additional overhead of the function call stack.

In order for the tail recursive call of a function to be optimized by the compiler, the following conditions need to be met:

• The tail recursive call must be the last action of the function.For example, the following function can be tail-recursive optimized:

int factorial(int n) { if (n <= 1) { return 1; } else { return n * factorial(n - 1); // 尾递归调用 } }

• The parameters and local variables of the function must remain unchanged across tail-recursive calls.For example, the following function cannot be tail-recursive optimized:

int sum(int n) { int result = 0; if (n > 0) { result += n; // 局部变量 result 在尾递归调用中发生变化 return sum(n - 1); } else { return result; } }

• The compiler must support TCO.Most modern C compilers, such as Clang and GCC, support TCO. However, please note that not all compilers support TCO.

Practical case

Consider the following function, which uses recursion to calculate the factorial:

int factorial(int n) { if (n == 0) { return 1; } else { return n * factorial(n - 1); } }

This function satisfies all conditions for tail-recursive optimization. We can use TCO to optimize this function and improve its performance.

int factorial(int n) { while (n > 0) { n = n * factorial(n - 1); // 转换为迭代 } return 1; }

After using TCO, the tail recursive call of the function is converted into a while loop. This eliminates the overhead of function calls and improves performance.

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