Formatting Strings

There's a pair of string functions that are particularly useful when you want to format data for display (such as when you're formatting numbers in string form): printf and sprintf. The printf function echoes text directly, and you assign the return value of sprintf to a string. Here's how you use these functions (items in square brackets, [ and ], in function specifications like this one are optional):

 printf (format [, args]) sprintf (format [, args]) 

The format string is composed of zero or more directives: characters that are copied directly to the result, and conversion specifications. Each conversion specification consists of a percent sign (%), followed by one or more of these elements, in order:

• An optional padding specifier that indicates which character should be used to pad the results to the correct string size. This may be a space character or a 0 (zero character). The default is to pad with spaces.

• An optional alignment specifier that indicates whether the results should be left- justified or right-justified. The default is right-justified (a - character here will make it left-justified).

• An optional number, the width specifier, specifying how many characters (minimum) this conversion should result in.

• An optional precision specifier that indicates how many decimal digits should be displayed for floating-point numbers. (There is no effect for types other than float.)

• A type specifier that says what type the argument data should be treated as.

Here are the possible type specifiers:

%	A literal percent character. No argument is required.
b	The argument is treated as an integer, and presented as a binary number.
c	The argument is treated as an integer, and presented as the character with that ASCII value.
d	The argument is treated as an integer, and presented as a (signed) decimal number.
u	The argument is treated as an integer, and presented as an unsigned decimal number.
f	The argument is treated as a float, and presented as a floating-point number.
-	The argument is treated as an integer, and presented as an octal number.
s	The argument is treated as and presented as a string.
x	The argument is treated as an integer and presented as a hexadecimal number (with lowercase letters).
X	The argument is treated as an integer and presented as a hexadecimal number (with uppercase letters).

These functions take a little getting used to, especially when you're formatting floating point values. For example, a format specifier of %6.2 means that a floating point number will be given six places in the display, with two places behind the decimal point. Here's an example that puts printf and sprintf to work:

 <?php     printf("I have %s apples and %s oranges.\n", 4, 56);     $year = 2005;     $month = 4;     $day = 28;     printf("%04d-%02d-%02d\n", $year, $month, $day);     $price = 5999.99;     printf("\$%01.2f\n", $price);     printf("%6.2f\n", 1.2);     printf("%6.2f\n", 10.2);     printf("%6.2f\n", 100.2);     $string = sprintf("Now I have %s apples and %s oranges.\n", 3, 5);     echo $string; ?> 

In this example, we're formatting simple integers as strings, aligning floating-point numbers vertically so the decimal point lines up, and so on. Here's what you see when you run this script at the command line:

 I have 4 apples and 56 oranges. 2005-04-28 $5999.99   1.20  10.20 100.20 Now I have 3 apples and 5 oranges. 

NOTE

Another function useful for formatting numbers is number_format().