PHP - string concatenation to produce a pattern

Question

I am new to PHP. I would like to generate the variable names based on the for loop condition value. This is my code.

  <?php
    for ( $i = 1; $i < $totalcolumns; $i++ ) 
{
  $pattern1 .= '\$'.'a'.$i'';
}
$pattern = str_repeat ('%d', $totalcolumns);

As per the above code, I have defined $pattern to generate %d as per the value of totalcolumns. The $pattern part is perfectly fine in the below loop.

while (fscanf ($file,'\''.$pattern.'\'','\''.$pattern1.'\''))

So if for example, my totalcolumns value is 3, the above while loop should get expanded as below.

while (fscanf ($file,'%d%d%d',$a1,$a2,$a3))

The pattern is getting expanded correctly, which I checked using echo statement. However, if I include the code for generating pattern1 my program doesn't produce any output.

I am trying to generate the pattern $a1, $a2, $a3 using the variable pattern1. I am using the string concatenation of PHP but I am not able to see any output in the screen. Can someone please guide me in the right direction?

Answer 1

<?php
$totalcolumns = 3
for ( $i = 1; $i <= $totalcolumns; $i++ ){
    $pattern1 .= '$a' . $i . ', ';
}
//remove the last comma and space.
$pattern1 = rtrim($pattern1, ", ");
echo $pattern1;
//$a1, $a2, $a3

based fully on: "I am trying to generate the pattern $a1, $a2, $a3"

I'm pretty sure you don't have to escape a dollar($) sign in single quotes either.

"\$"

'$'

Then if I wanted to do something with the output

<?php
$filledInString = str_replace('$a1', "REPLACED!", $pattern1);
$filledInString = str_replace('$a3', "AGAIN!", $filledInString);
echo $filledInString;
//REPLACED!, $a2, AGAIN!
?>

Or you could just be looking for variable variables, but maybe this is what you were after. Dunno, hope it helped :-)

Answer 2

May be try this :

<?php
// You probably might have code here to populate $totalcolumns .
// For test purpose I assumed a value .
    $totalcolumns = 3;

//  Initialize $pattern1
    $pattern1 = '';
//  Make sure weather you need $i < $totalcolumns or $i <= $totalcolumns
    for ( $i = 1; $i < $totalcolumns; $i++ ) 
    {
    //  Your line was $pattern1 .= '\$'.'a'.$i''; which has systax error due to two single quotes before the semicolon
        $pattern1 .= '\$'.'a'.$i;
    }
    echo $pattern1;

Will output :

\$a1\$a2

The above answers your ( actual ) question . But it seems that your need is to call a function with variable number of parameters . If it is the case call_user_func_array could help you in something along these lines :

call_user_func_array
Variable variables
How to pass variable number of arguments to a PHP function

<?php
// You probably might have code here to populate $totalcolumns .
// For test purpose I assumed a value .
    $totalcolumns = 3;

//  Also assuming some values for $a1, $a2, $a3 etc.
    $a1 = 'abc';
    $a2 = 'pqr';
    $a3 = 'xyz';

//  For test purpose I used a string replace it with the actual file handle
    $file = 'File handle';

//  Initialize $pattern
    $pattern = '';

//  Define an array to hold parameters for call_user_func_array
    $parameterArray = array();

//  Put first parameter of fscanf at index 0 of $parameterArray
    $parameterArray[0] = $file;

//  Initialize second parameter of fscanf at index 1 of $parameterArray
    $parameterArray[1] = $pattern;

    $parameterArrayIndex = 2;
    for ( $i = 0; $i < $totalcolumns; $i++ ) 
    {
        $pattern .= '%d';
        $parameterArray[$parameterArrayIndex] = ${"a".($i+1)};  // Variable variables
        $parameterArrayIndex++;
    }

//  Update second parameter of fscanf at index 1 of $parameterArray
    $parameterArray[1] = $pattern;

    var_dump( $parameterArray );

    while( call_user_func_array( 'fscanf', $parameterArray ) )
    {
        //  Do what ever you need to do here
    }