Home  >  Article  >  Backend Development  >  Why does a modified constant variable retain its original value at compile time, even though a non-const pointer allows for modification of its actual value?

Why does a modified constant variable retain its original value at compile time, even though a non-const pointer allows for modification of its actual value?

Mary-Kate Olsen
Mary-Kate OlsenOriginal
2024-11-01 19:33:02561browse

Why does a modified constant variable retain its original value at compile time, even though a non-const pointer allows for modification of its actual value?

Modifying a Constant through a Non-Const Pointer

In the given code, a constant variable e is initialized to 2. A non-const pointer w is then cast to point to the address of e, implicitly removing the const-ness of the variable. By dereferencing w and assigning a new value to it, the value at the address of e is modified from 2 to 5.

However, when the values of *w and e are printed, they appear different:

<code class="cpp">cout << *w << endl; // Outputs 5
cout << e << endl; // Outputs 2</code>

This behavior can be explained by considering the different ways in which *w and e are evaluated:

  • *w is being evaluated at runtime: The compiler recognizes that *w is a non-const pointer and dynamically retrieves the value at the address pointed to by w. Since the value at that address has been modified to 5, *w correctly outputs 5.
  • e is being treated as a compile-time constant: The compiler recognizes that e is a constant variable and evaluates its value at compile time. Since the value of e has not been modified at compile time, the compiler continues to treat it as 2.

Therefore, the difference in values arises from the distinct evaluation times of *w and e. Despite the modification to the value at the address of e, the constant variable itself remains unmodified at compile time. However, the non-const pointer w allows for modification of the value at the address it points to, resulting in the output of 5 for *w.

The above is the detailed content of Why does a modified constant variable retain its original value at compile time, even though a non-const pointer allows for modification of its actual value?. For more information, please follow other related articles on the PHP Chinese website!

Statement:
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn