Usage const modifier in function

Question

From the linux kernel scripts/mod/modpost.c:

static int is_vmlinux(const char *modname)
{
    const char *myname;

    myname = strrchr(modname, '/');
    if (myname)
            myname++;
    else
            myname = modname;

    return (strcmp(myname, "vmlinux") == 0) ||
           (strcmp(myname, "vmlinux.o") == 0);
}

How I understand:

This is defining the pointer to type of char and the const modifier. This pointer cannot be changed. But on the next lines we change the pointer.

Is it correct? Looks like no. :(

Why in this code use const? What doing here const? Can we write it without const?

See answer here: https://stackoverflow.com/a/1446150/8513665 — Christian Gibbons, Jul 02 '18 at 17:12
Possible duplicate of [const usage with pointers in C](https://stackoverflow.com/questions/1446120/const-usage-with-pointers-in-c) — Lion King, Jul 02 '18 at 17:41
In C, you read each variable declaration from right to left, and `*` as *"a pointer to"*. So, `const char *myname` is read as *"myname is a pointer to const char"*. On the other hand, `char *const myname` is *"myname is a const pointer to char"*. — Nominal Animal, Jul 02 '18 at 19:23

score 6 · Accepted Answer · answered Jul 02 '18 at 17:19

const char * myname;

is a pointer to constant (content). You are allowed to modify the pointer. e.g. myname = NULL, myname++, but modification of the content is not possible.

char * const myname;

is a constant pointer. The opposite is possible. You are not allowed to modify the pointer, but you are allowed to modify what it points to e.g. *myname ^= ' ', which makes letter upper case if it is lower case.

Usage const modifier in function

1 Answers1