这个功能会泄漏内存吗？

Question

The function below tests if the input string contains a double.

bool is_double(const std::string& str)
{
    char* p;
    strtod(str.c_str(), &p);
    return *p == 0;
}

What happens to pointer p after the function returns?

Answer 1

You have two variables to consider: str and p .

The string str is passed as a const reference, so it's lifetime must be managed outside the scope of this function, so it cannot be leaked by this function.

With the character pointer p , we can consider the pointer itself and what it points to. According to the documentation, it is set to "...point to the first character after the number." Meaning, it points to memory inside the string you've passed; it does not get set to newly allocated memory. Since you're already managing the lifetime of str properly, and nothing new has been allocated, you don't have to free what it points to. The pointer variable itself is created on the stack, so its lifetime is that of the function.

So, no, you're not leaking.

Answer 2

A resource leak happens when you allocate a resource that becomes unreachable outside a certain scope and you didn't free it nor can get back a reference to it, whether that resource is dynamic memory, mutexes, or any other process-bound resource.

In your case, you're creating some variables and using a function that doesn't do any dynamic memory allocation so all of your stuff are in the stack => no memory leak because it's "freed" once you return from the function.

Answer 3

由于指针在函数范围内并且未被声明为全局，我相信它将在执行函数后自动擦除。

Answer 4

pointer p will is set by the function to the next character in str after the numerical value.

so it won't leak memory

also you can use

bool is_double(const std::string& str)
{
   double d;
   d = strtod(str.c_str(), NULL);
   return d != 0.0;
}