PHP 面试题与答案
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相关差异对比
问题 11. How come the code <?php print "Contents: $arr[1]"; ?> works, but <?php print "Contents: $arr[1][2]"; ?> doesn't for two-dimensional array of mine? -
Any time you have an array with more than one dimension, complex parsing syntax is required. print "Contents: {$arr[1][2]}" would've worked.
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问题 12. What is the difference between characters 23 and x23?
The first one is octal 23, the second is hex 23.
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问题 13. With a heredoc syntax, do I get variable substitution inside the heredoc contents?
Yes.
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问题 14. I want to combine two variables together:
$var1 = 'Welcome to '; $var2 = 'TechInterviews.com';What will work faster? Code sample 1: -
$var 3 = $var1.$var2;Or code sample 2:
$var3 = "$var1$var2";Both examples would provide the same result - $var3 equal to "Welcome to TechInterviews.com". However, Code Sample 1 will work significantly faster. Try it out with large sets of data (or via concatenating small sets a million times or so), and you will see that concatenation works significantly faster than variable substitution.
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问题 15. For printing out strings, there are echo, print and printf. Explain the differences.
echo is the most primitive of them, and just outputs the contents following the construct to the screen. print is also a construct (so parentheses are optional when calling it), but it returns TRUE on successful output and FALSE if it was unable to print out the string. However, you can pass multiple parameters to echo, like:
<?php echo 'Welcome ', 'to', ' ', 'TechInterviews!'; ?>and it will output the string "Welcome to TechInterviews!" print does not take multiple parameters. It is also generally argued that echo is faster, but usually the speed advantage is negligible, and might not be there for future versions of PHP. printf is a function, not a construct, and allows such advantages as formatted output, but it's the slowest way to print out data out of echo, print and printf.
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