PHP fprintf() Function

Topic: PHP String ReferencePrev|Next

Description

The fprintf() function writes a formatted string to a stream, usually a file.

This function takes a special format string and then any number of other arguments, which will be formatted and spliced into the specified places in the format string to generate the result.

Related functions: printf(), sprintf(), vfprintf(), vprintf() and vsprintf().

The following table summarizes the technical details of this function.

Syntax

The basic syntax of the fprintf() function is given with:

The following example shows the fprintf() function in action.

<?php
$file = "data.txt";

// Open the file for writing
$handle = fopen($file, "w") or die("ERROR: Cannot open the file.");

// Sample strings
$count = 50;
$country = "United States";
$format = "There are %d states in the %s.";

// Formatting and write the string to file
$length = fprintf($handle, $format, $count, $country);

echo "Wrote $length bytes to data.txt";
?>

The output of the above example will look something like this:

And, the text written to the file "data.txt" will be:

In the above example, if the "data.txt" file doesn't exist PHP will automatically create it and write the data. But, if the "data.txt" file already exist, PHP will erase the contents of this file, if it has any, before writing the new data. See the tutorial on PHP file system to learn more about it.

Parameters

The fprintf() function accepts the following parameters.

Conversion Specification Syntax

This section describes the syntax of conversion specification in the format string in detail.

A conversion specification begins with a percent symbol (%). You must include a conversion specification for each argument that is passed to the fprintf() function after the format string.

Alternatively, you can use the argument number followed by a dollar sign (i.e. argnum$) to apply multiple conversion specifications in the format string to the same argument. It must come immediately after the percent sign (%), before any other specifiers. See more examples section.

A conversion specification typically has the following syntax:

argnum

An integer followed by a dollar sign $, to specify which number argument to treat in the conversion.

flags

The flags consist of one or more of the following characters:

width

An integer that indicates how many characters (minimum) this conversion should result in.

precision

A period (.) followed by an integer who's meaning depends on the specifier:

• For e, E, f and F specifiers: this is the number of digits to be printed after the decimal point (by default, this is 6).
• For g and G specifiers: this is the maximum number of significant digits to be printed.
• For s specifier: it acts as a cutoff point, setting a maximum character limit to the string.

If the period is specified without an explicit value for precision, 0 is assumed.

specifier

A single character indicating how the type of the argument should be interpreted.

More Examples

Here're some more examples showing how fprintf() function actually works:

The following example shows how to apply multiple conversion specifications to the same argument.

<?php
$file = "data.txt";

// Open the file for writing
$handle = fopen($file, "w") or die("ERROR: Cannot open the file.");

// Sample string
$str = 'star';
$format = 'The polar %1$s is the brightest %1$s in the sky.';

// Formatting and write the string to file
$length = fprintf($handle, $format, $str);

echo "Wrote $length bytes to data.txt";
?>

The output of the above example will look something like this:

And, the text written to the file "data.txt" will be:

The following example shows how to format the same number with and without decimal points.

<?php
$file = "data.txt";

// Open the file for writing
$handle = fopen($file, "w") or die("ERROR: Cannot open the file.");

// Sample string
$number = 499;
$format = "The number without decimal points: %1\$d, and the number with two decimal points: %1\$.2f";

// Formatting and write the string to file
$length = fprintf($handle, $format, $number);

echo "Wrote $length bytes to data.txt";
?>

The output of the above example will look something like this:

And, the text written to the file "data.txt" will be:

By default, each conversion specification will be replaced by the formatted argument in the order they are listed inside the function. But, you can swap arguments inside the format string using argnum.

<?php
$file = "data.txt";

// Open the file for writing
$handle = fopen($file, "w") or die("ERROR: Cannot open the file.");

// Sample strings
$count = 50;
$country = "United States";
$format = "The %2\$s is a federal republic of %1\$d states.";

// Formatting and write the string to file
$length = fprintf($handle, $format, $count, $country);

echo "Wrote $length bytes to data.txt";
?>

The output of the above example will look something like this:

And, the text written to the file "data.txt" will be:

The following example simply demonstrates what would be the possible outcome when using the different format specifiers for integer values using the printf() function.

<?php
// Sample integers
$num1 = 123456789;
$num2 = -123456789;
$num3 = 65; // ASCII 65 is 'A'

// Notice the double %%, this simply prints a '%' character
printf("%%b = %b <br>", $num1); // Binary representation
printf("%%c = %c <br>", $num3); // The ASCII Character
printf("%%d = %d <br>", $num1); // Standard integer representation
printf("%%d = %d <br>", $num2); // Standard integer representation
printf("%%e = %e <br>", $num1); // Scientific notation (lowercase)
printf("%%E = %E <br>", $num1); // Scientific notation (uppercase)
printf("%%u = %u <br>", $num1); // Unsigned integer representation (positive)
printf("%%u = %u <br>", $num2); // Unsigned integer representation (negative)
printf("%%f = %f <br>", $num1); // Floating-point representation (locale aware)
printf("%%F = %F <br>", $num1); // Floating-point representation (non-locale aware)
printf("%%g = %g <br>", $num1); // Shorter of %e and %f
printf("%%G = %G <br>", $num1); // Shorter of %E and %f
printf("%%o = %o <br>", $num1); // Octal representation
printf("%%s = %s <br>", $num1); // String representation
printf("%%x = %x <br>", $num1); // Hexadecimal representation (lowercase)
printf("%%X = %X <br>", $num1); // Hexadecimal representation (uppercase)
printf("%%+d = %+d <br>", $num1); // Sign specifier (positive)
printf("%%+d = %+d <br>", $num2); // Sign specifier (negative)
?>

Similarly, the following example shows how to format a string in various ways using s specifier.

<?php
$str1 = "Hello";
$str2 = "Hello Alexander!";

printf("[%s]<br>", $str1);     // Standard string output
printf("[%10s]<br>", $str1);   // Right-justifies the string with spaces
printf("[%-10s]<br>", $str1);  // Left-justifies the string value with spaces
printf("[%010s]<br>", $str1);  // Left-pads string with zeros.
printf("[%-010s]<br>", $str1); // Right-pads string with zeros
printf("[%'#10s]<br>", $str1); // Left-pads string with '#' character
printf("[%.10s]<br>", $str2);  // Cuts off string after 10 characters
?>