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On 9/21/2010 8:03 PM, Pete Becker wrote:
> On 2010-09-21 13:52:04 -0400, Paul said:
>
>> I have a path in a string ie: std::string s =
>> "/usr/local/src/test.dat"
>>
>> Is there a string function that will locate the last "/" in a string and
>> null terminate the string on that character?
>>
>
> start with basic_string::rfind.
>

While rfind is perfectly fine I think find_last_of states in the intent
ever so slightly clearer.

std::string str = "/usr/local/src/test.dat";
std::string::size_type end = str.find_last_of('/');
if(end != str.npos)
str = str.substr(0, end+1);

If you need a null terminated string i.e. a C-string, you can use
str.c_str().

On 9/21/2010 8:21 PM, Paul wrote:
> On 2010-09-21, Stefan van Kessel<> wrote:
>> On 9/21/2010 8:03 PM, Pete Becker wrote:
>>> On 2010-09-21 13:52:04 -0400, Paul said:
>>>
>>>> I have a path in a string ie: std::string s =
>>>> "/usr/local/src/test.dat"
>>>>
>>>> Is there a string function that will locate the last "/" in a string and
>>>> null terminate the string on that character?
>>>>
>>>
>>> start with basic_string::rfind.
>>>
>>
>> While rfind is perfectly fine I think find_last_of states in the intent
>> ever so slightly clearer.
>>
>> std::string str = "/usr/local/src/test.dat";
>> std::string::size_type end = str.find_last_of('/');
>> if(end != str.npos)
>> str = str.substr(0, end+1);
>>
>> If you need a null terminated string i.e. a C-string, you can use
>> str.c_str().
> I like that method! Very clear to understand.
>
Actually str.erase(end+1) would be better than assigning the substr. I
didn't think of that before. But be sure to test if the character has
actually been found (here end!=str.npos) unless you already know for
sure it is in the string.
sbackup.replace(sbackup.rfind("/"), sbackup.length(), "");
which you wrote in the other message produces undefined behavior if
there is no "/" in the string because replace requires the first
argument to be smaller than the size of the string.

On 9/21/2010 11:14 PM, Pete Becker wrote:
> On 2010-09-21 14:11:54 -0400, Stefan van Kessel said:
>
>> On 9/21/2010 8:03 PM, Pete Becker wrote:
>>> On 2010-09-21 13:52:04 -0400, Paul said:
>>>
>>>> I have a path in a string ie: std::string s =
>>>> "/usr/local/src/test.dat"
>>>>
>>>> Is there a string function that will locate the last "/" in a string
>>>> and
>>>> null terminate the string on that character?
>>>>
>>>
>>> start with basic_string::rfind.
>>>
>>
>> While rfind is perfectly fine I think find_last_of states in the
>> intent ever so slightly clearer.
>
> Um, not hardly. And it's bigger and slower. rfind does exactly what's
> needed.
>

I'm not sure why you are convinced that it's "bigger and slower". If
there is more to it than the following, I would love to hear about it.
The standard requires the same behavior of both:
They both ought to behave as if they forward to their overload taking a
basic_string containing that one char.
(From 21.3.6
- Effects: Determines the highest position xpos, if possible, such that
both of the following conditions obtain:
rfind:
— xpos <= pos and xpos + str.size() <= size();
— at(xpos+I) == str.at(I) for all elements I of the string controlled by
str.
find_last_of:
— xpos <= pos and xpos < size();
— at(xpos) == str.at(I) for some element I of the string controlled by str.

With str.size() == 1 that amounts to the same.

In practice both the implementations that I checked: msvc10's and gcc
4.5's basic_string::find_last_of are a one line function, defined
inline, that does nothing but forward the call to rfind.

MSVC:
size_type find_last_of(_Elem _Ch, size_type _Off = npos) const
{ // look for _Ch before _Off
return (rfind((const _Elem *)&_Ch, _Off, 1));
}

While rfind('/') merely forwards to the same version of rfind, too:
size_type rfind(_Elem _Ch, size_type _Off = npos) const
{ // look for _Ch before _Off
return (rfind((const _Elem *)&_Ch, _Off, 1));
}

GCC:
* Note: equivalent to rfind(c, pos).
*/
size_type
find_last_of(_CharT __c, size_type __pos = npos) const
{ return this->rfind(__c, __pos); }


So find_last_of will not be faster than rfind but *usually* not slower
either. Anybody who doesn't agree that find_last_of might state the
intent clearer (and I don't feel strongly about that either; I admit
that it's hardly more than a bikeshed issue anyway :/) absolutely should
go with rfind but I'm not convinced that performance is a killer
argument here.

Have a nice day,
Stefan

On Sep 21, 10:14 pm, Pete Becker <p...@versatilecoding.com> wrote:
> On 2010-09-21 14:11:54 -0400, Stefan van Kessel said:

> > On 9/21/2010 8:03 PM, Pete Becker wrote:
> >> On 2010-09-21 13:52:04 -0400, Paul said:

> >>> I have a path in a string ie: std::string s =
> >>> "/usr/local/src/test.dat"

> >>> Is there a string function that will locate the last "/"
> >>> in a string and null terminate the string on that
> >>> character?

> >> start with basic_string::rfind.

> > While rfind is perfectly fine I think find_last_of states in
> > the intent ever so slightly clearer.

> Um, not hardly. And it's bigger and slower. rfind does exactly
> what's needed.

Until he has to port to Windows, and find either '/' or '\' .

(I'll admit that I don't find anything using the std::string
member functions "clearer". I have to know the algorithms in
<algorithm> anyway, for the cases where I'm dealing with some
other sort of container. Why should a learn a separate and
distinct set just for std::string?)

--
James Kanze