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Хостинг:
stdarg - variable argument lists
The called function must declare an object of type
va_list
which is used by the macros
va_start (,);
va_arg (,);
va_copy (,);
and
va_end (.);
The
va_start ();
macro initializes
Fa ap
for subsequent use by
va_arg ();
and
va_end (,);
and must be called first.
The parameter Fa last is the name of the last parameter before the variable argument list, i.e., the last parameter of which the calling function knows the type.
Because the address of this parameter is used in the
va_start ();
macro, it should not be declared as a register variable, or as a
function or an array type.
The
va_start ();
macro returns no value.
The
va_arg ();
macro expands to an expression that has the type and value of the next
argument in the call.
The parameter
Fa ap
is the
va_list Fa ap
initialized by
va_start (.);
Each call to
va_arg ();
modifies
Fa ap
so that the next call returns the next argument.
The parameter
Fa type
is a type name specified so that the type of a pointer to an
object that has the specified type can be obtained simply by
adding a *
to
Fa type .
If there is no next argument, or if Fa type is not compatible with the type of the actual next argument (as promoted according to the default argument promotions), random errors will occur.
The first use of the
va_arg ();
macro after that of the
va_start ();
macro returns the argument after
Fa last .
Successive invocations return the values of the remaining
arguments.
The
va_copy ();
macro copies a variable argument list, previously initialized by
va_start (,);
from
Fa src
to
Fa dest .
The state is preserved such that it is equivalent to calling
va_start ();
with the same second argument used with
Fa src ,
and calling
va_arg ();
the same number of times as called with
Fa src .
The
va_copy ();
macro returns no value.
The
va_end ();
macro handles a normal return from the function whose variable argument
list was initialized by
va_start (.);
The
va_end ();
macro returns no value.
void foo(char *fmt, ...)
{
va_list ap;
int d;
char c, *s;
va_start(ap, fmt);
while (*fmt)
switch(*fmt++) {
case 's': /* string */
s = va_arg(ap, char *);
printf("string %s\n", s);
break;
case 'd': /* int */
d = va_arg(ap, int);
printf("int %d\n", d);
break;
case 'c': /* char */
/* Note: char is promoted to int. */
c = va_arg(ap, int);
printf("char %c\n", c);
break;
}
va_end(ap);
}
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