Compatibility of pointer assignment

This title is not accurate. Today, from expert C programming, it seems that the title has been moved to unknown places, and a bunch of things have been read in disorder. Let's start with expert C programming.

Today I read the beginning of this article, mainly in section 1.9.

Foo (const char ** p ){}

Main (INT argc, char ** argv)
{
Foo (arvg );
}

A warning is displayed: The parameter does not match the prototype. That is to say, char ** and const char ** are incompatible. However, char * and const char * are compatible. Why is char * compatible with const char * (char * P2 can assign a value to const char * P1), because the objects indicated by P1 and P2 are both char and compatible; p1 has const and P2 does not, which is also compatible because it complies with the rule that "the left value of the assignment between pointers must contain all the right-value qualifiers. But for const char ** P1 and char ** P2, the situation is different. Although P1 still complies with the rule that "the left value contains all qualified words of the right value", the object that P1 points to is a pointer to the const object, the object indicated by P2 is a pointer to a non-const object. The two types are incompatible, so p1 = P2 is invalid.

(From: http://blog.csdn.net/megaboy/archive/2005/10/17/505927.aspx)

In short, the const char * and char * pointer types are incompatible.

 

What is a compatible definition? If you see one on the internet, it makes sense: the type is compatible, which means the type is different, but the system can automatically convert it. That is to say, the system cannot automatically convert char * to const char *. In fact, I think this rule is quite strange. The char * and const char * pointers do not have any qualifier, but they only point to the object with a qualifier, one pointing to Char and the other pointing to const char.

That is to say, P1 is essentially a pointer Q1, and P2 also points to a pointer Q2. It is a pointer. Why is it incompatible. If the incompatibility is because Q1 and Q2 point to different objects, this is obviously a conflict. char * Q2 and const char * Q1 are obviously compatible. Therefore, this rule is simply strange. I don't know what the starting point is.

Obviously, there will be no perfect standards, and there will always be some minor problems.