How to dynamically create a string in PHP?

Question

I have a predefined pattern for building a string, which should be created regularly throughout the script.

$str="$first - $second @@ $third"; // pattern for building the string
$first="word1";
$second="word2";
$third="word3";
$string= ..?? // string should be built here based on the pattern

Currently, I am using eval to generate the string in place based on the pattern originally defined. However, as this happens occasionally and eval is generally bad, I wish to find another method.

NOTE that the pattern is defined only one time above all codes, and I can edit the pattern of all the script by one line only. Thus, what makes $string should not be touched for any change.

I tried create_function, but needs the same number of arguments. With eval, I can easily change the pattern, but with create-function, I need to change the entire script. For example, if changing the string pattern to

$str="$first @@ $second"; // One arg/var is dropped

eval Example:

$str="$first - $second @@ $third"; // Pattern is defined one-time before codes
$first="word1";
$second="word2";
$third="word3";
eval("\$string = \"$str\";");

create_function Example:

$str=create_function('$first,$second,$third', 'return "$first - $second @@ $third";');
$string=$str($first,$second,$third);

Could you give your example with eval please? It's a little difficult to understand what exactly you're trying to do, since the last string declaration looks like it should work for what you want. — FThompson
– FThompson, Commented Nov 6, 2012 at 5:34
Thanks, they helped clarify your question quite a bit, and I've answered the question. — FThompson
– FThompson, Commented Nov 6, 2012 at 6:00

FThompson · Accepted Answer · 2012-11-06 06:00:08Z

3

You can use the string formatting capabilities offered by sprintf or vsprintf.

$format = "%s - %s @@ %s"; // pattern for building the string
$first = "word1";
$second = "word2";
$third = "word3";
$string = sprintf($format, $first, $second, $third);

You can use vsprintf if you wish to pass an array.

$format = "%s - %s @@ %s"; // pattern for building the string
$values = array($first, $second, $third);
$string = vsprintf($format, $values);

answered Nov 6, 2012 at 6:00

FThompson

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3 Comments

Googlebot Over a year ago

subtle solution, but what if changing the order of variables in the pattern? for example: $str="$second-$first"; then, we need to change the sprintf pattern too throughout the script.

FThompson Over a year ago

You can specify in the format what argument number to refer to: $str = "%2$s-%1$s". That would place the second (third including the $format itself) argument before the first in the output order.

Googlebot Over a year ago

Now, it's a practical solution. I appreciate your subtle view to mention sprintf, which is the key function for patterning strings, but I blindly ignored.

Starx · Accepted Answer · 2012-11-06 05:41:23Z

0

Seems to be rather simple thing to me. Use str_replace() and replace based on patterns

$str="$first$ - $second$ @@ $third$"; // pattern for building the string
$first="word1";
$second="word2";
$third="word3";

$newstr = str_replace('$first$', $first, $str);
$newstr = str_replace('$second$', $second, $newstr);
$newstr = str_replace('$third$', $third, $newstr);

answered Nov 6, 2012 at 5:41

Starx

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1 Comment

Googlebot Over a year ago

1. The pattern is not always simple, 2. I want to make change only to the pattern, but by your method, I need to modify $newstr throughout the script, and many many times.

web-nomad · Accepted Answer · 2012-11-06 05:47:18Z

0

This might help, not sure.

$str = "_first_ - _second_ @@ _third_"; // pattern for building the string
// _first, _second_... are placeholders for actual values

// this function performs the string building
function buildString( $arr ) {
   global $str;

   $keys = array_keys( $arr );
   $vals = array_values( $arr );

   return eval( str_replace( $keys, $vals, $str ) );
}

while(some condition here) {
    $str = 'A new string'; // you can change your string builiding pattern here

    // this array is built in the fashion ->
    // keys of array are the variables in $str and
    // their actual values are the values of $str
    $arr=array('_first_' => $first, '_second_' => $second, '_third_' => $third);
    echo buildString( $arr );
}

answered Nov 6, 2012 at 5:47

web-nomad

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1 Comment

Googlebot Over a year ago

Currently, eval works perfectly. The point is that eval is not a good thing. I want to do this without eval, but your function is based on eval too.

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