Curly braces in string in PHP

Question

What is the meaning of      curly braces  in string literals in PHP

User · Answer

Example    number   4  print  You have the   number th edition book     output   You have the 4th edition book     Without curly braces PHP would try to find a variable named  numberth  that doesn t exist

User · Answer

As for me  curly braces serve as a substitution for concatenation  they are quicker to type and code looks cleaner  Remember to use double quotes       as their content is parsed by PHP  because in single quotes       you ll get the literal name of variable provided    lt  php    a    12345       This works   echo  qwe  a rty      qwe12345rty  using braces  echo  qwe     a    rty      qwe12345rty  concatenation used     Does not work   echo  qwe  a rty      qwe  a rty  single quotes are not parsed  echo  qwe arty      qwe  because  a became  arty  which is undefined    gt

User · Answer

I ve also found it useful to access object attributes where the attribute names vary by some iterator  For example  I have used the pattern below for a set of time periods  hour  day  month    periods array  hour    day    month    foreach   periods as  period         this- gt   value    period  1      This same pattern can also be used to access class methods  Just build up the method name in the same manner  using strings and string variables   You could easily argue to just use an array for the value storage by period  If this application were PHP only  I would agree  I use this pattern when the class attributes map to fields in a database table  While it is possible to store arrays in a database using serialization  it is inefficient  and pointless if the individual fields must be indexed  I often add an array of the field names  keyed by the iterator  for the best of both worlds   class timevalues                                   Database table values      public  value hour          maps to values value hour     public  value day           maps to values value day     public  value month         maps to values value month     public  values array         public function   construct                  this- gt value hour 0           this- gt value day 0           this- gt value month 0           this- gt values array               hour   gt  this- gt value hour               day   gt  this- gt value day               month   gt  this- gt value month

User · Answer

This is the complex  curly  syntax for string interpolation  From the manual      Complex  curly  syntax      This isn t called complex because the syntax is complex  but because   it allows for the use of complex expressions       Any scalar variable  array element or object property with a string   representation can be included via this syntax  Simply write the   expression the same way as it would appear outside the string  and   then wrap it in   and    Since   can not be escaped  this syntax   will only be recognised when the   immediately follows the    Use       to get a literal     Some examples to make it clear    lt  php    Show all errors error reporting E ALL     great    fantastic       Won t work  outputs  This is   fantastic  echo  This is    great        Works  outputs  This is fantastic echo  This is   great    echo  This is   great        Works echo  This square is   square- gt width 00 centimeters broad          Works  quoted keys only work using the curly brace syntax echo  This works    arr  key           Works echo  This works    arr 4  3         This is wrong for the same reason as  foo bar  is wrong  outside a string     In other words  it will still work  but only because PHP first looks for a    constant named foo  an error of level E NOTICE  undefined constant  will be    thrown  echo  This is wrong    arr foo  3          Works  When using multi-dimensional arrays  always use braces around arrays    when inside of strings echo  This works    arr  foo   3         Works  echo  This works       arr  foo   3    echo  This works too    obj- gt values 3 - gt name     echo  This is the value of the var named  name      name      echo  This is the value of the var named by the return value of getName       getName        echo  This is the value of the var named by the return value of   object- gt getName        object- gt getName           Won t work  outputs  This is the return value of getName     getName    echo  This is the return value of getName     getName        gt     Often  this syntax is unnecessary  For example  this    a    abcd    out     a  a       abcd abcd     behaves exactly the same as this    out      a    a       same   So the curly braces are unnecessary  But this    out     aefgh     will  depending on your error level  either not work or produce an error because there s no variable named  aefgh  so you need to do    out      a efgh      or  out      a efgh

[php] Curly braces in string in PHP

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