Re: [PHP-DEV] preg_match() option for anchored offset?

[Rasmus Schultz]

> You are looking for the \G anchor or the A modifier.

Both of these options work great!

I've submitted a patch to the manual page with a note explaining these
options.

Thanks :-)


On Wed, Jun 7, 2017 at 10:13 PM, Nikita Popov  wrote:

> On Wed, Jun 7, 2017 at 10:03 PM, Rasmus Schultz 
> wrote:
>
>> What do you think about adding another option to preg_match() to allow the
>> $offset parameter to be treated as the start anchor?
>>
>> The manual proposes to do this:
>>
>> $subject = "abcdef";
>> $pattern = '/^def/';
>> $offset = 3;
>> preg_match($pattern, substr($subject, $offset), $matches);
>>
>> In other words, use substr() to copy the entire remainder of the string.
>>
>> I just wrote a simple SQL parser tonight, and had to use this approach,
>> which (I imagine) must be pretty inefficient?
>>
>> I'd like to be able to do the following:
>>
>> $subject = "abcdef";
>> $pattern = '/^def/';
>> $offset = 3;
>> preg_match($pattern, $subject, $matches, PREG_ANCHOR_OFFSET, $offset);
>>
>> This new option would make the ^ anchor work from the given $offset, which
>> allows me to parse the entire $subject without copying anything.
>>
>> Thoughts?
>>
>
> You are looking for the \G anchor or the A modifier.
>
> Nikita
>
>

Re: [PHP-DEV] preg_match() option for anchored offset?

[Nikita Popov]

On Wed, Jun 7, 2017 at 10:03 PM, Rasmus Schultz  wrote:

> What do you think about adding another option to preg_match() to allow the
> $offset parameter to be treated as the start anchor?
>
> The manual proposes to do this:
>
> $subject = "abcdef";
> $pattern = '/^def/';
> $offset = 3;
> preg_match($pattern, substr($subject, $offset), $matches);
>
> In other words, use substr() to copy the entire remainder of the string.
>
> I just wrote a simple SQL parser tonight, and had to use this approach,
> which (I imagine) must be pretty inefficient?
>
> I'd like to be able to do the following:
>
> $subject = "abcdef";
> $pattern = '/^def/';
> $offset = 3;
> preg_match($pattern, $subject, $matches, PREG_ANCHOR_OFFSET, $offset);
>
> This new option would make the ^ anchor work from the given $offset, which
> allows me to parse the entire $subject without copying anything.
>
> Thoughts?
>

You are looking for the \G anchor or the A modifier.

Nikita

Re: [PHP-DEV] preg_match() option for anchored offset?

[Rowan Collins]

On 07/06/2017 21:03, Rasmus Schultz wrote:

What do you think about adding another option to preg_match() to allow the
$offset parameter to be treated as the start anchor?

The manual proposes to do this:

 $subject = "abcdef";
 $pattern = '/^def/';
 $offset = 3;
 preg_match($pattern, substr($subject, $offset), $matches);

In other words, use substr() to copy the entire remainder of the string.

I just wrote a simple SQL parser tonight, and had to use this approach,
which (I imagine) must be pretty inefficient?

I'd like to be able to do the following:

 $subject = "abcdef";
 $pattern = '/^def/';
 $offset = 3;
 preg_match($pattern, $subject, $matches, PREG_ANCHOR_OFFSET, $offset);

This new option would make the ^ anchor work from the given $offset, which
allows me to parse the entire $subject without copying anything.

Thoughts?



How would you propose to implement this? Is it something PCRE already 
supports? Or would you manipulate the subject string pointer at the 
point it's passed down? The latter approach seems doable, but I'm not 
sure if there are any subtle gotchas.


Regards,

--
Rowan Collins
[IMSoP]


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[PHP-DEV] preg_match() option for anchored offset?

[Rasmus Schultz]

What do you think about adding another option to preg_match() to allow the
$offset parameter to be treated as the start anchor?

The manual proposes to do this:

$subject = "abcdef";
$pattern = '/^def/';
$offset = 3;
preg_match($pattern, substr($subject, $offset), $matches);

In other words, use substr() to copy the entire remainder of the string.

I just wrote a simple SQL parser tonight, and had to use this approach,
which (I imagine) must be pretty inefficient?

I'd like to be able to do the following:

$subject = "abcdef";
$pattern = '/^def/';
$offset = 3;
preg_match($pattern, $subject, $matches, PREG_ANCHOR_OFFSET, $offset);

This new option would make the ^ anchor work from the given $offset, which
allows me to parse the entire $subject without copying anything.

Thoughts?