Rainer Weikusat <[email protected]> writes:
> Didier Kryn <[email protected]> writes:
>
> [...]
>
>>> A multi-line version could look like this:
>>>
>>> while (c = *r) {
>>> ++r;
>>> if (c == '/') n = r;
>>> }
>>>
>>
>> It might be done with a for loop. eg:
>>
>> for ( ; *r ; ++r) if(*r=='/') n=r;
>> n++;
>
> [...]
>
>> The for loop is the best construct for a loop with an incremental
>> cursor.
>
> That's nicely exemplified by the fact that the code above does a
> redundant increment (or did a redundant increment would it work, the {}
> are missing) solely to work around
[...]
> the "for loop
While making fun of other people's statements in this way may be ... well
... fun, it's not very nice and also not exactly useful.
A C 'for loop' is a pretty strange control construct (one could call it
'overly generic'). It's definition (from K&R 2nd ed) is
for (expression1; expression2; expression3) statement
is equivalent to
expression1;
while (expression2) {
statement
expression3;
}
[in absence of a continue in 'statement']
That's a generalization of a loop with the abstract structure
<init stmts>;
while (<test expr>) {
<body stmts>;
<step stmts>;
}
with
<init stmts>
Sequence of statements intializing a set of loop control
variables.
<test expr>
Test expression. Used to compare loop control variables or
values depending on loop control variables with a termination
condition (or 'continuation condition' for C). If the loop
should execute once more, the
<body stmts>,
a sequence of statements making up the loop body, are
executed. These may perform operation depending on the current
value of loop control variables but don't modify them
themselves.
<step stmts>
Sequence of statements changing the loop control variables
possibly based on results from the <body stmts> to 'the next
state' prior to evualting the <test expr> again.
but the C for (;;;) doesn't enforce any of these semantic conventions
but is really more of a macro which tranposes the text inside the (;;;)
as indicated above. Each of the expressions of a for (;;;) may contain
arbitrary C expressions, ie, anything except C control constructs.
If one happens to be writing a loop following the abstract description
given above, for (;;;) can be used to express it fairly
straight-forwardly if it isn't too complicated. The 'classic' example
would be the C-approximation of a counting loop,
for (int i = 0; i < 10; i++) printf("%d\n", i);
But the loop in
static char const *get_name(char const *arg0)
{
char const *n, *r;
n = r = arg0;
while (*r) if (*r++ == '/') n = r;
return n;
}
is not of this type. It contains an init-statement,
n = r = arg0;
followed by a test expression,
while (*r)
followed by another test of the same value,
if (*r == '/')
followed by a step-statement,
if (*r++ == '/)
followed by an assignment which should only be executed if the test was
true but which should use the value modified by the step expression.
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