Page 117 - Programming Microcontrollers in C

102 Chapter 2 Advanced C Topics

The function prototype of the function malloc() is contained
in stdlib.h. This function returns a pointer to a type void. If
you will recall the rules of arithmetic for pointers, a pointer to a type
void can be assigned to any other pointer type, and vice versa. There­
fore, it is not necessary to cast the return from the malloc call to
the type char* as was done above. In fact, there are people that say
that you should not perform this cast. If you make a mistake and
do not include the header stdlib.h, then the compiler would as­
sume that the return from the malloc function call is an int. The
cast operation would introduce a bug into your code if the header
were not included. The error of the missing header file would be
identified by the compiler if there is no cast because the program
would be loathe to assign an integer to a pointer. Therefore, the code
without the cast is more robust.
I personally object to this logic. The current trend is to insist that
all operands in expressions that are not of the correct type be cast
to the correct type prior to execution of any operators. This trend
largely ignores the automatic type promotion that takes place when
there are mixed types within a single expression. In fact, many pro­
gramming standards insist that all mixed types be cast explicitly. In
such an environment, it seems rather silly that one case be singled
out and done differently.
The function talloc() also makes use of the malloc()
function. In this case, the argument of the malloc() call is the
sizeof operator. sizeof is a C operator that returns the size of
the argument. sizeof is an operator in C and requires no prototype.
/* talloc : make a tnode */
TNODE *talloc(void)
{
return (TNODE *) malloc(sizeof(TNODE));
}
The memory allocation function malloc() returns a pointer to
the basic memory size of the system. It is always necessary to cast
the return from malloc() onto the type of variable that the return
must point to. In this case, the cast is to the type pointer to TNODE.
In strsave(), the cast was to the type pointer to char. There­
fore, the statement