问题
Regarding performance, is there any difference between doing:
$message = "The request $request has $n errors";
and
$message = sprintf('The request %s has %d errors', $request, $n);
in PHP?
I would say that calling a function involves more stuff, but I do not know what's PHP doing behind the scenes to expand variables names.
Thanks!
回答1:
In all cases the second won't be faster, since you are supplying a double-quoted string, which have to be parsed for variables as well. If you are going for micro-optimization, the proper way is:
$message = sprintf('The request %s has %d errors', $request, $n);
Still, I believe the seconds is slower (as @Pekka pointed the difference actually do not matter), because of the overhead of a function call, parsing string, converting values, etc. But please, note, the 2 lines of code are not equivalent, since in the second case $n is converted to integer. if $n is "no error" then the first line will output:
The request $request has no error errors
While the second one will output:
The request $request has 0 errors
回答2:
It does not matter.
Any performance gain would be so minuscule that you would see it (as an improvement in the hundreths of seconds) only with 10000s or 100000s of iterations - if even then.
For specific numbers, see this benchmark. You can see it has to generate 1MB+ of data using 100,000 function calls to achieve a measurable difference in the hundreds of milliseconds. Hardly a real-life situation. Even the slowest method ("sprintf() with positional params") takes only 0.00456 milliseconds vs. 0.00282 milliseconds with the fastest. For any operation requiring 100,000 string output calls, you will have other factors (network traffic, for example) that will be an order of magniture slower than the 100ms you may be able to save by optimizing this.
Use whatever makes your code most readable and maintainable for you and others. To me personally, the sprintf() method is a neat idea - I have to think about starting to use that myself.
回答3:
A performance analysis about "variable expansion vs. sprintf" was made here.
As @pekka says, "makes your code most readable and maintainable for you and others". When the performance gains are "low" (~ less than twice), ignore it.
Summarizing the benchmark: PHP is optimized for Double-quoted and Heredoc resolutions. Percentuals to respect of average time, to calculating a very long string using only,
- double-quoted resolution: 75%
- heredoc resolution: 82%
- single-quote concatenation: 93%
- sprintf formating: 117%
- sprintf formating with indexed params: 133%
Note that only sprintf do some formating task (see benchmark's '%s%s%d%s%f%s'), and as @Darhazer shows, it do some difference on output. A better test is two benchmarks, one only comparing concatenation times ('%s' formatter), other including formatting process — for example '%3d%2.2f' and functional equivalents before expand variables into double-quotes... And more one benchmark combination using short template strings.
PROS and CONS
The main advantage of sprintf is, as showed by benchmarks, the very low-cost formatter (!). For generic templating I suggest the use of the vsprintf function.
The main advantages of doubled-quoted (and heredoc) are some performance; and some readability and maintainability of nominal placeholders, that grows with the number of parameters (after 1), when comparing with positional marks of sprintf.
The use of indexed placeholders are at the halfway of maintainability with sprintf.
NOTE: not use single-quote concatenation, only if really necessary. Remember that PHP enable secure syntax, like "Hello {$user}_my_brother!", and references like "Hello {$this->name}!".
回答4:
For Injecting Multiple String variables into a String, the First one will be faster.
$message = "The request $request has $n errors";
And For a single injection, dot(.) concatenation will be faster.
$message = 'The request '.$request.' has 0 errors';
Do the iteration with a billion loop and find the difference.
For eg :
<?php
$request = "XYZ";
$n = "0";
$mtime = microtime(true);
for ($i = 0; $i < 1000000; $i++) {
$message = "The request {$request} has {$n} errors";
}
$ctime = microtime(true);
echo ($ctime-$mtime);
?>
回答5:
I am surprised, but for PHP 7.* "$variables replacement" is the fastest approach:
$message = "The request {$request} has {$n} errors";
You can simply prove it yourself:
$request = "XYZ";
$n = "0";
$mtime = microtime(true);
for ($i = 0; $i < 1000000; $i++) {
$message = "The request {$request} has {$n} errors";
}
$ctime = microtime(true);
echo '
"variable $replacement timing": '. ($ctime-$mtime);
$request = "XYZ";
$n = "0";
$mtime = microtime(true);
for ($i = 0; $i < 1000000; $i++) {
$message = 'The request '.$request.' has '.$n.' errors';
}
$ctime = microtime(true);
echo '
"concatenation" . $timing: '. ($ctime-$mtime);
$request = "XYZ";
$n = "0";
$mtime = microtime(true);
for ($i = 0; $i < 1000000; $i++) {
$message = sprintf('The request %s has %d errors', $request, $n);
}
$ctime = microtime(true);
echo '
sprintf("%s", $timing): '. ($ctime-$mtime);
The result for PHP 7.3.5:
"variable $replacement timing": 0.091434955596924
"concatenation" . $timing: 0.11175799369812
sprintf("%s", $timing): 0.17482495307922
Probably you already found recommendations like 'use sprintf instead of variables contained in double quotes, it’s about 10x faster.' What are some good PHP performance tips?
I see it was the truth but one day. Namely before the PHP 5.2.*
Here is a sample of how it was those days PHP 5.1.6:
"variable $replacement timing": 0.67681694030762
"concatenation" . $timing: 0.24738907814026
sprintf("%s", $timing): 0.61580610275269
回答6:
Ultimately the 1st is the fastest when considering the context of a single variable assignment which can be seen by looking at various benchmarks. Perhaps though, using the sprintf flavor of core PHP functions could allow for more extensible code and be better optimized for bytecode level caching mechanisms like opcache or apc. In other words, a particular sized application could use less code when utilizing the sprintf method. The less code you have to cache into RAM, the more RAM you have for other things or more scripts. However, this only matters if your scripts wouldn't properly fit into RAM using evaluation.
来源：https://stackoverflow.com/questions/7147305/performance-of-variable-expansion-vs-sprintf-in-php