Why the first argument of fread() be cast to other type in

Question

Here is the program:

FILE *fp;
struct record rec;
while (fread((char *)&rec, sizeof(rec), 1, fp) == 1) // Here
{
    /* do something to rec */
    if (/*rec must be rewritten*/) 
    {
        fseek(fp, -(long)sizeof(rec), 1);
        fwrite((char*)&rec, sizeof(rec), 1, fp);  // And here
    }
}

Look at the notes, the author says:

It looks reasonable enough at first glance: &rec is carefully cast to char * to pass to fread and fwrite...

I can't understand the meaning.

Answer 1

Firstly, don't attempt to use SO ** markup inside code blocks. It doesn't work as intended and it only creates confusion.

Secondly, the book is apparently outdated. Back in the very old versions of C language there was no void * type and char * type was typically used instead as "generic" pointer type. The first parameter of fread was declared with char * type. For this reason it was customary to perform explicit cast of actual argument type to char * to avoid compiler warnings. It might even be necessary today, if an old version of standard library is used (one that declares fread with char * parameter).

Modern C standard library declares fread with first parameter of type void *. No cast is necessary in that case and cast to char * makes no sense at all.