[Original] const and pointer usage in C language, original const

[Original] const and pointer usage in C language, original const

I have been preparing for the written examination recently to make up for my class in arrears. I encountered this question when I reviewed the C language:

 

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int a=248, b=4;int const c=21;const int *d=&a; int *const e=&b;int const * const f =&a;

 

Which of the following expressions will be forbidden by the compiler?

A：*c=32

B:*d=43

C: e = &

D: f = 0x321f

E: d = & B

F: * e = 34


The following are analyzed one by one
The first line of code is not mentioned. The second line,int const c=21; And const int c = 21; indicates that c is modified to const, that is, the value of c cannot be changed. So A must be wrong. c is not A pointer;
Row 3:const int * D = & a; indicates that the value pointed to by d cannot be changed through the pointer, So B: * d = 43 is incorrect. The direction of d is variable. HERE d = & a, E: d = & B is also correct;
Row 4:int *const E = & B; indicates that the point of pointer e cannot be changed, so C is wrong. However, the point value can be changed. * e = 34 is correct, and F is correct;
Fifth line:int const * const F = & a; indicates that neither the pointing or pointing content of pointer f can be changed. D is incorrect.
The answer is ABCD.

Here, Baidu encyclopedia introduces a method:

If the const is on the left side of *, the value of the variable pointed to by the pointer cannot be changed directly through the pointer (it can be changed through other means); if the value is on the right side of *, the pointer cannot be changed. Note: "Left value, right direction"

However, be sure to note that int * const p; int const * const p; or const int * const p; the Pointer Points cannot be changed and an address must be initialized during definition.

Basically, const is okay ~