关于结构体成员指针：(*pmovie).title与*(pmovie.title)的区别求解

Hey there! This is a super common gotcha that all comes down to C++ operator precedence—the order the compiler uses to evaluate operations. Let’s break this down step by step with a concrete example to make it crystal clear.

First, let’s assume we’re working with a simple Movie struct like this:

#include <string>

struct Movie {
    std::string title;
    int release_year;
};

// And a pointer pointing to an instance of this struct:
Movie* pmovie = new Movie{"The Matrix", 1999};

1. (*pmovie).title – The Correct Way to Access a Struct Member via Pointer #

• The parentheses () force the compiler to evaluate *pmovie first. This dereferences the pointer, meaning we get the actual Movie struct object that pmovie is pointing to.
• Next, we use the . member access operator to grab the title member of that struct. This works exactly as you’d expect—we end up with the string "The Matrix".

As a handy shortcut, C++ gives us pmovie->title which does the exact same thing as (*pmovie).title—it’s the standard, cleaner way to write this in practice.

2. *(pmovie.title) – This Will (Almost Always) Fail to Compile #

Here’s where the precedence rule trips people up: the . member access operator has higher priority than the * dereference operator. That means the compiler tries to evaluate pmovie.title first, before it ever gets to the *.

But wait—pmovie is a pointer (Movie*), not a Movie struct instance. Pointers don’t have a title member! The compiler will throw an error like:

error: 'Movie*' has no member named 'title'

Even if pmovie was a struct that had a title member (say, a different struct containing a pointer), *(pmovie.title) would dereference whatever pmovie.title points to—not the title of the original Movie struct we care about. In your original context, this is almost certainly a mistake.

Key Takeaway #

Always remember: . and -> have higher precedence than *. If you’re using * to dereference a struct pointer before accessing a member, you must wrap the dereference in parentheses to override the default precedence. Or better yet, use the -> syntax—it avoids this confusion entirely.

内容的提问来源于stack exchange，提问作者Peter Ye