ID Number: Q73850
5.10 6.00 6.00a 6.00ax 7.00 | 5.10 6.00 6.00a
MS-DOS | OS/2
Summary:
SYMPTOMS
In Microsoft C versions 5.1, 6.0, 6.0a, 6.0ax, and C/C++ 7.0,
variables may be declared as local to a switch statement by
defining them within the braces that make up the switch. They
then have visibility and life for the duration of the switch
statement. However, because of the design of a switch block,
they will not be initialized when declared unless the variable
is static or is declared after a case label.
RESOLUTION
If you must declare an initialized variable that is local to the
switch statement and transient in duration, use brackets before and
after the switch and place the declaration outside the switch
statement.
More Information:
The ANSI Standard (Section 3.6.4.2) states:
A "switch" statement causes control to jump to, into, or past
the statement that is the switch body, depending on the value
of a controlling expression, and on the presence of a "default"
label and the values of any "case" labels on or in the switch
body. A "case" or "default" label is accessible only within the
closest enclosing "switch" statement.
The integral promotions are performed on the controlling
expression. The constant expression in each "case" label is
converted to the promoted type of the controlling expression.
If a converted value matches that of the promoted controlling
expression, control jumps to the statement following the
matched "case" label. Otherwise, if there is a "default" label,
control jumps to the labeled statement. If no converted case
constant expression matches and there is no default label, no
part of the switch body is executed.
The sample code below illustrates this. To have the variable
local_int initialized to the correct value (5 in this case), you have
two choices. If it must be an automatic variable, you have to either
declare it outside the switch statement (with parentheses to limit
scope) or after each case that you wish to use it. If the variable
does not have to be automatic, merely declare it as static.
Sample Code
-----------
/* Compile options needed: none
*/
int _cdecl printf(const char *, ...);
void switch_func(int);
int main(void);
int rc = 0;
int main(void)
{
switch_func(100);
if (rc)
printf("Failed\n");
else
printf("Passed\n");
return(rc);
}
void switch_func(int param)
{
switch (param)
{
int local_int = 5;
case 100:
local_int+=5;
rc = (local_int == 10 ? 0 : 1);
break;
default:
break;
}
}
Additional reference words: QuickC 2.0 2.00 2.01 2.5 2.50 2.51 6.0
6.00 6.0a 6.00a 6.0ax 6.00ax 7.00