I'm from a C background and understand basics of printf function.
I came across the follwing code
<?php
printf('%4$d %2$s code for %3$3.2f %1$s', "hours", "coders", 9, 99);
?>
which prints:
99 coders code for 9.00 hours
Can anyone help me in understanding the call to the printf function.
<n>$ means "use the nth argument, instead of whatever position you are in formatting specs".
The first argument of the printf function is a String that gets altered using the other arguments:
%4d - takes the 4th item after the comma and treats it as a decimal number
%2$s - takes the 2nd item after the comma and treats it as a String
%3$3.2f - takes the 3rd itam after the comma and treats it as a floating number with two decimal places
%1$s - takes the first item after the comma and treats it as a String
Ignacio's answer is correct.
One very useful application of this feature if you're using gettext for I18N. The order of substitution might change between one language and another. (though if you're wrapping stuff in calls to gettext, you'd be using sprintf).
I'm drawing a blank on a real-world example, guess I don't speak enough natural languages.
I think some of the confusion might have been an error in the code:
%3$3.2f should read %3$.2f instead (but it works either way).
Not sure what the difficulty is, because it's fairly well documented in the manual:
The first argument is the format mask, subsequent arguments are values to insert into the format mask. Rules for masking are the same as in C. And like in C, output is sent directly to stdout
Related
I’m trying to parse some strings in some messed-up CSV files (about 100,000 rows per file). Some columns have been squished together in some rows, and I’m trying to get them unsquished back into their proper columns. Part of the logic needed there is to find whether a substring in a given colum is numeric or not.
Non-numeric strings can be anything, including strings that happen to begin with a number; numeric strings are generally written the European way, with dots used for thousand separators and commas for decimals, so without going through a bunch of string replacements, is_numeric() won’t do the trick:
\var_dump(is_numeric('3.527,25')); // bool(FALSE)
I thought – naïvely, it transpires – that the right thing to do would be to use NumberFormatter::parse(), but it seems that function doesn’t actually check whether the string given as a whole is parseable as a numeric string at all – instead it just starts at the beginning and when it reaches a character not allowed in a numeric string, cuts off the rest.
Essentially, what I’m looking for is something that will yield this:
$formatter = new \NumberFormatter('de-DE', \NumberFormatter::DECIMAL);
\var_dump($formatter->parse('3.527,25')); // float(3527.25)
\var_dump($formatter->parse('3thisisnotanumber')); // bool(FALSE)
But all I can get is this:
$formatter = new \NumberFormatter('de-DE', \NumberFormatter::DECIMAL);
\var_dump($formatter->parse('3.527,25')); // float(3527.25)
\var_dump($formatter->parse('3thisisnotanumber')); // float(3)
I figured perhaps the problem was that the LENIENT_PARSE attribute was set to true, but setting it to false ($formatter->setAttribute(\NumberFormatter::LENIENT_PARSE, 0)) has no effect; non-numeric strings still get parsed just fine as long as they begin with a number.
Since there are so many rows and each row may have as many as ten columns that need to be validated, I’m looking at upwards of a million validations per file – for that reason, I would prefer avoiding a preg_match()-based solution, since a million regex match calls would be quite expensive.
Is there some way to tell the NumberFormatter class that you would like it to please not be lenient and only treat the string as parseable if the entire string is numeric?
You can strip all the separators and check if whatever remains is a numeric value.
function customIsNumeric(string $value): bool
{
return is_numeric(str_replace(['.', ','], '', $value));
}
Live test available here.
You can use is_numeric() to check that it is only numbers before parsing. But NumberFormatter does not do what you are looking for here.
Just a note to begin I am aware that ereg_replace() is deprecated, since POSIX is no longer being used. But in "Beginning PHP and MySQL" by W Jason Gilmore, Gilmore emphasizes that although POSIX isn't to be used, an understanding is still necessary as a means of conversion to Perl. So once again I understand it's deprecated but since I'm trying to understand everything in the book I might as well understand this.
So the example is as follows:
<?php
$text = "This is a link to http://www.example.com/.";
echo ereg_replace("http://([a-zA-Z0-9./-]+)$", "\\0",
$text);
?>
//Output
This is a link to http://www.example.com/..
So I understand the majority of code in the above example, my problem lies with the ./- and the output. For the ./- I tried to think according to quantifiers where . = between, so everything between [:alnum:] and / is replaced. I also thought maybe ./- are characters within the range which would also be replaced since [:alnum:] doesn't include punctuation. For verfication I looked at the output but theres no - present. If only the / is replaced than the code would make sense, since /0 outputs http://www.example.com/ but than the problem lies with the missing - which I presume to be pertinent to the brackets rather than as a quantifier.
My other question is in regards to the output, if the function returns the string with the modified string why does the period which was present in the original string appear after the second /0, not the first, if its the original text, why does the tag follow it and not precede it?
Just for some quick background, I have a basic understanding of php,html,css,javascript,C++ and I'm reading this for a more in depth understanding of php and an introduction to MySQL, so unfortunately explanations which are entirely advanced code/concepts go right over my head.
why does the period which was present in the original string appear after the second /0, not the first
This is not the case, because the actual output is:
This is a link to http://www.example.com/.
The period is included in both the attribute as well as the tag contents.
my problem lies with the ./- and the output
When present inside a character set, ./- means to match either a period, forward slash or a dash; it's important to note that the dash must appear at the end of the character set to avoid ambiguity.
I'm working through some more PHP tutorials, specifically DevZone PHP 101, and am confused by:
echo .sprintf("%4.2f", (2 * $radius * pi()))
I found this
I think that means produce a floating-point field four positions wide with two decimal places, using the value of the first succeeding parameter.
That comes from the C/C++ line of programming languages. an sprintf() takes the first parameter as a format statement. Anything in it starting with a % is a field specifier; anything else is just printable text. So if you give a format statement with all text and no specifiers, it will print exactly the way it appears. With format specifiers, it needs data to work on.
But after trying some different values I'm still not getting it. It seems to me if the purpose of it in this case is just to limit the decimal to 2 places all I have to put is
.sprintf("%.2f", (2 * $radius * pi()))
What is the point of the 4 in the front of it? In the PHP Manual it leads me to believe it determines the total number of characters should be 4 but (a) thats not the case since the decimal point makes it 5 characters and (b) thats not the case because I tried changing it to a larger number like %8.2f and it didn't tack any zeros on to either end. Could someone please better explain this.
Thanks!
The first number %8.2f in the format specifier is for the filling length. Per default sprintf uses the space character.
You can see the effect with larger numbers:
printf("%20.2f", 1.23);
Will for example lead to:
1.23
There's 16 spaces before the number. The float takes up 4, and the fill length was set to 20 for instance. (Maybe you printed it out into the webpage, thus no padding spaces were visible..)
And there's an example further below on the sprintf manpage to use alternative padding characters:
printf("%'*20.2f", 1.23); // use the custom padding character '*'
Will result in:
****************1.23
So I am working on a simple micro language/alternative syntax for PHP.
Its syntax takes a lot from JavaScript and CoffeeScript including a few of my own concepts. I have hand written the parser (no parser generator used) in PHP to convert the code into PHP then execute it. It is more of a proof of concept/learning tool rather than anything else but I'd be lying if I said I didn't want to see it used on an actual project one day.
Anyway here is a little problem I have come across that I thought I would impose on you great intellects:
As you know in PHP the period ( . ) is used for string concatenation. However in JavaScript it is used for method chaining.
Now one thing that annoys me in PHP is having to do use that bloody arrow (->) for my method chains, so I went the JavaScript way and implemented the period (.) for use with objects.
(I think you can see the problem already)
Because I'm currently only writing a 'dumb' parser that merely does a huge search and replace, there is no way to distinguish whether a period (.) is being used for concatenation or for method chaining.
"So if you are trying to be like JavaScript, just use the addition (+) operator Franky!", I hear you scream. Well I would but because the addition (+) operator is used for math in PHP I would merely be putting myself in the same situation.
Unless I can make my parser smart enough (with a crap load of work) to know that when the addition (+) operator is working with integers then don't convert it into a period (.) for concatenation I am pretty much screwed.
But here is the cool thing. Because this is pretty much a new language. I don't have to use the period or addition operator for concatenation.
So my question is: If I was to decide to introduce a new method of string concatenation, what character would make the most sense?
Does it have to be one character? .. could work!
Any myriad of combinations, like ~~ or >: even!
If you don't want to use + or ., then I would recommend ^ because that's used in some other languages for string concatenation and I don't believe that it's used for anything in PHP.
Edit: It's been pointed out that it's used for XOR. One option would be to use ^ anyway since bitwise XOR is not commonly used and then to map something else like ^^ to XOR. Another option would be to use .. for concatenation. The problem is that the single characters are mostly taken.
Another option would be to use +, but map it to a function which concatenates when one argument is a string and adds otherwise. In order to not break things which rely on strings which are numbers being treated as their values, we should probably treat numeric strings as numbers for these purposes. Here's the function that I would use.
function smart_add($arg1,$arg2) {
if ($arg1.is_numeric() && $arg2.is_numeric()) {
return $arg1 + $arg2;
} else {
return $arg1 . $arg2;
}
}
Then a + b + c + d just gets turned into smart_add(smart_add(smart_add(a,b),c),d)
This may not be perfect in all cases, but it should work pretty well most of the time and has clear rules for use.
So my question is: If I was to decide to introduce a new method of
string concatenation, what character would make the most sense?
As you're well aware of, you'll need to chose a character that is not being used as one of PHP's operators. Since string concatenation is a common technique, I would try to avoid using characters that you need to press SHIFT to type, as those characters will be a hindrance.
Instead of trying to assign one character for string concatenation (as most are already in use), perhaps you should define your own syntax for string concatenation (or any other operation you need to overwrite with a different operator), as a shorthand operator (sort of). Something like:
[$string, $string]
Should be easy to pick up by a parser and form the resulting concatenated string.
Edit: I should also note that whether you're using literal strings or variables, there's no way (as far as I know) to confuse this syntax with any other PHP functionality, since the comma in the middle is invalid for array manipulations. So, all of the following would still be recognized as string concatenation and not something else in PHP.
["stack", "overflow"]
["stack", $overflow]
[$stack, $overflow]
Edit: Since this conflicts to JSON notation, the following alternative variations exist:
Changing the delimiter
Omitting the delimiter
Example:
[$stack $overflow $string $concatenation] // Use nothing (but really need space)
I have to replace xmlns with ns in my incomming xml in order to fix SimpleXMLElements xpath() function. Most functions do not have a performance problem. But there allways seems to be an overhead as the string grows.
E.g. preg_replace on a 2 MB string takes 50ms to process, even if I limit the replaces to 1 and the replace is done at the very beginning.
If I substr the first few characters and just replace that part it is slightly faster. But not really that what I want.
Is there any PHP method that would perform better in my problem? And if there is no option, could a simple php extension help, that just does Replace => SimpleXMLElement in C?
If you know exactly where the offending "x", "m" and "l" are, you can just use something like $xml[$x_pos] = ' '; $xml[$m_pos] = ' '; $xml[$l_pos] = ' ' to transform them into spaces. Or transform them into ns___ (where _ = space).
You're always going to get an overhead when trying to do this - you're dealing with a char array and trying to do replace multiple matching elements of the array (i.e. words).
50ms is not much of an overhead, unless (as I suspect) you're trying to do this in a loop?
50ms sounds pretty reasonable to me, for something like this. The requirement itself smells of something being wrong.
Is there any particular reason that you're using regular expressions? Why do people keep jumping to the overkill regex solution?
There is a bog-standard string replace function called str_replace that may do what you want in a fraction of the time (though whether this is right for you depends on how complex your search/replace is).
From the PHP source, as we can see, for example here:
http://svn.php.net/repository/php/php-src/branches/PHP_5_2/ext/standard/string.c
I don`t see, any copies, but I'm not expert in C. From the other hand we can see there many convert to string calls, which at 1st sight could copy values. If they copy values, then we in trouble here.
Only if we in trouble
Try to invent some str_replace wheel here with the help of string-by-char processing. For example we have string $somestring = "somevalue". In PHP we could work with it's chars by indexes as echo $somestring{0}, which will give us "s" or echo $somestring{2} which will give us "m". I'm not sure in this way, but it's possible, if official implimentations don't use references, as they should use.