Why value looks different with printf and echo

Question

I’m making a calculation between dates and times but when displaying the value with printf the result is one and with echo is different. With this calculation the value is displayed correctly:

 $Entrada = strtotime( '2010-05-26 08:00' );
    $Saida   = strtotime( '2010-05-26 11:15' );
    $Diferenca = $Saida - $Entrada;

    $hora = $Diferenca/3600;
    $min  = $Diferenca/60%60;

    printf( '%d:%d', $hora, $min );

The result is: 3:15

And thus the result is added a value at the end:

    $Entrada = strtotime( '2010-05-26 08:00' );
    $Saida   = strtotime( '2010-05-26 11:15' );
    $Diferenca = $Saida - $Entrada;

    $hora = $Diferenca/3600;
    $min  = $Diferenca/60%60;

    $Resultado = printf( '%d:%d', $hora, $min );
    echo $Resultado;

The result is: 3:154

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Answer 1

The printf is a function that prints a formatted string in the console and returns the string length in numbers.

For example:

// Irá mostrar a string "Luiz Felipe" antes dos três hífens.
$printedLength = printf("%s %s", "Luiz", "Felipe");

echo "\n" . "---" . "\n";

// Irá imprimir 11:
echo $printedLength;

^{See it working on Ideone.}

If you want to assign the value of a formatted string, you should use the function sprintf, which does not print to the stdout automatically:

// Irá atribuir a string "Luiz Felipe" à variável `$formated`:
$formated = sprintf("%s %s", "Luiz", "Felipe");

// Irá imprimir "Luiz Felipe" ao console:
echo $formated;

^{See it working on Ideone.}

---

That way, when you do:

$resultado = printf('%d:%d', $hora, $min);
echo $resultado;

You are printing the time to stdout and then printing the length of the formatted string (which has already been printed on the console).

In the above case, you probably want to replace the function printf for sprintf:

$resultado = sprintf('%d:%d', $hora, $min);
echo $resultado;

Reference:

• printf;
• sprintf.

Answer 2

As I noticed, when you use %d you are asking the printf to show the absolute integer, then when you put everything together in the "%d:%d", there is 0.25 minutes left of the hour, this leftover is placed in the minutes, so that, 15 + 0.25 ((60/4) minutes that represents the leftover) generate the 03:154 probably by rounding.

Use gmdate to format differently if desired.

<?php
// Inteiros com timestamp inicial.
$Entrada = strtotime('2010-05-01 08:00');
// Inteiros com timestamp finaç.
$Saida = strtotime('2010-05-01 11:15');
// diferença.
$Diferenca = $Saida - $Entrada;
// Conversão de tempos.
$hora = $Diferenca / 3600;
$min = $hora / 60 % 60;
// formatar como GMT:UTC Date/Time.
$Resultado = gmdate('H:i', $Diferenca);
// Mostrar resultado
echo $Resultado; // A saída será 03:15
?>