This chapter describes both functions that work on arbitrary arrays or blocks of memory, and functions that are specific to null-terminated arrays of characters and wide characters.
Functions that operate on arbitrary blocks of memory have names
beginning with `mem' and `wmem' (such as
wmemcpy) and invariably take an argument which specifies the size
(in bytes and wide characters respectively) of the block of memory to
operate on. The array arguments and return values for these functions
void * or
wchar_t. As a matter of style, the
elements of the arrays used with the `mem' functions are referred
to as “bytes”. You can pass any kind of pointer to these functions,
sizeof operator is useful in computing the value for the
size argument. Parameters to the `wmem' functions must be of type
wchar_t *. These functions are not really usable with anything
but arrays of this type.
In contrast, functions that operate specifically on strings and wide
character strings have names beginning with `str' and `wcs'
respectively (such as
wcscpy) and look for a
null character to terminate the string instead of requiring an explicit
size argument to be passed. (Some of these functions accept a specified
maximum length, but they also check for premature termination with a
null character.) The array arguments and return values for these
functions have type
char * and
wchar_t * respectively, and
the array elements are referred to as “characters” and “wide
In many cases, there are both `mem' and `str'/`wcs' versions of a function. The one that is more appropriate to use depends on the exact situation. When your program is manipulating arbitrary arrays or blocks of storage, then you should always use the `mem' functions. On the other hand, when you are manipulating null-terminated strings it is usually more convenient to use the `str'/`wcs' functions, unless you already know the length of the string in advance. The `wmem' functions should be used for wide character arrays with known size.
Some of the memory and string functions take single characters as
arguments. Since a value of type
char is automatically promoted
into an value of type
int when used as a parameter, the functions
are declared with
int as the type of the parameter in question.
In case of the wide character function the situation is similarly: the
parameter type for a single wide character is
wint_t and not
wchar_t. This would for many implementations not be necessary
wchar_t is large enough to not be automatically
promoted, but since the ISO C standard does not require such a
choice of types the
wint_t type is used.