php, sprintf and Memory Usage
I was going through some legacy code for a client and ran across a whole bunch of calls to sprintf(). The calls were all similiar to the below:
$query = sprintf('SELECT * FROM table WHERE field1 = "%s" AND field2 = "%s" LIMIT 1',$var1, $var2);
It seemed an odd use to call the above instead of the straight forward, and low impact, way of declaring the variable.
$query = "SELECT * FROM table WHERE field1 = '$var1' AND field2 = '$var2' LIMIT 1";
I've never really had the need to use sprintf() so I'm not familiar with it enough to know much so I asked a colleague of mine, Devin, "What process would require the use of sprintf?". According to Devin, sprintf is used for complicated and dynamic formatting. Here's an example from the php manual on the subject:
<?php $n = 43951789; $u = -43951789; $c = 65; // ASCII 65 is 'A' // notice the double %%, this prints a literal '%' character printf("%%b = '%b'\n", $n); // binary representation printf("%%c = '%c'\n", $c); // print the ascii character, same as chr() function printf("%%d = '%d'\n", $n); // standard integer representation printf("%%e = '%e'\n", $n); // scientific notation printf("%%u = '%u'\n", $n); // unsigned integer representation of a positive integer printf("%%u = '%u'\n", $u); // unsigned integer representation of a negative integer printf("%%f = '%f'\n", $n); // floating point representation printf("%%o = '%o'\n", $n); // octal representation printf("%%s = '%s'\n", $n); // string representation printf("%%x = '%x'\n", $n); // hexadecimal representation (lower-case) printf("%%X = '%X'\n", $n); // hexadecimal representation (upper-case) printf("%%+d = '%+d'\n", $n); // sign specifier on a positive integer printf("%%+d = '%+d'\n", $u); // sign specifier on a negative integer ?>
The above outputs:
%b = '10100111101010011010101101' %c = 'A' %d = '43951789' %e = '4.39518e+7' %u = '43951789' %u = '4251015507' %f = '43951789.000000' %o = '247523255' %s = '43951789' %x = '29ea6ad' %X = '29EA6AD' %+d = '+43951789' %+d = '-43951789'
Pretty cool, but I'm not still not sure what the purpose of using sprintf() like the first example demonstrated would accomplish. Surely, there must be some sort of performance penalty, right? According to a programmer Devin used to work, there's a HUGE penalty for using sprintf. To find out I wrote a simple test script, that's the farthest thing from scientific, to just get a generic baseline on memory usage and sprintf().
<?php for($i=0;$i<100000;$i++){ //Call sprintf } echo filesize_format(memory_get_usage()); echo '<br>'; echo filesize_format(memory_get_peak_usage()); function filesize_format($bytes, $format = '%01.5lf %s', $force = '') { $force = strtoupper($force); $defaultFormat = '%01d %s'; if (strlen($format) == 0) $format = $defaultFormat; $bytes = max(0, (int) $bytes); $units = array('B', 'KB', 'MB', 'GB', 'TB', 'PB'); $power = array_search($force, $units); if ($power === false) { $power = $bytes > 0 ? floor(log($bytes, 1024)) : 0; } return sprintf($format, $bytes / pow(1024, $power), $units); } ?>
First the baseline. This is without running the loop.
/*
Baseline of 0 loops just php start stop:
Total: 71.39062 KB
Peak: 76.84375 KB
*/Next, I did a run of sprintf() calls like the below:
/* Total: 73.76562 KB Peak: 77.22656 KB */ for($i=0;$i<100000;$i++){ $t = 'SELECT col1,col2,col3 FROM table WHERE col1="1" AND col2="2" LIMIT 1'; }
Followed by a straight variable declaration:
/* Total: 72.82812 KB Peak: 77.17969 KB */ for($i=0;$i<100000;$i++){ $t = 'SELECT col1,col2,col3 FROM table WHERE col1="1" AND col2="2" LIMIT 1'; }
Huh... the numbers don't really add up to all that much. I really thought it'd be more of a difference than that. Well, just to be sure I ran two more tests like the above, except with 4 variables being created instead of 1.
/* Peak: 76.69531 KB Peak: 78.28125 KB */ for($i=0;$i<100000;$i++){ $t = sprintf('SELECT col1,col2,col3 FROM table WHERE col1="%s" AND col2="%s" LIMIT 1','1', '2'); $r = sprintf('SELECT col1,col2,col3 FROM table WHERE col1="%s" AND col2="%s" LIMIT 1','1', '2'); $k = sprintf('SELECT col1,col2,col3 FROM table WHERE col1="%s" AND col2="%s" LIMIT 1','1', '2'); $o = sprintf('SELECT col1,col2,col3 FROM table WHERE col1="%s" AND col2="%s" LIMIT 1','1', '2'); }
And
/* Peak: 73.95312 KB Peak: 77.48438 KB */ for($i=0;$i<100000;$i++){ $t = 'SELECT col1,col2,col3 FROM table WHERE col1="1" AND col2="2" LIMIT 1'; $r = 'SELECT col1,col2,col3 FROM table WHERE col1="1" AND col2="2" LIMIT 1'; $k = 'SELECT col1,col2,col3 FROM table WHERE col1="1" AND col2="2" LIMIT 1'; $o = 'SELECT col1,col2,col3 FROM table WHERE col1="1" AND col2="2" LIMIT 1'; }
Look at that; nothing. There doesn't appear to be any significant increase in memory in relation to usage. For a loop that runs 100,000 times compared to a memory increase of only about 1 KB this really isn't bad. Use sprintf if you want to.
Oh yeah, Devin you were lied to 
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I wonder if I was lied to…..appears from your testing that there is not a big hit in memory. Anyone else ?
Using your example as a base I ran a trial using sprintf to format a string that was about nine megs. Over 1000 loops sprintf wound up using over six more megs than using simple string concatenation.
I guess sprintf really shouldn’t be used with data that large.
It undoubtedly does take quite some time to find fantastic data like this. Thanks a lot. Best Regards http://lifecellskin.org/free-cosmetic-samples/