参数

format

The format string is composed of zero or more directives: ordinary characters (excluding %) that are copied directly to the result, and conversion specifications, each of which results in fetching its own parameter. This applies to both sprintf() and printf().

Each conversion specification consists of a percent sign (%), followed by one or more of these elements, in order:

1. An optional sign specifier that forces a sign (- or +) to be used on a number. By default, only the - sign is used on a number if it's negative. This specifier forces positive numbers to have the + sign attached as well, and was added in PHP 4.3.0.
2. An optional padding specifier that says what character will be used for padding the results to the right string size. This may be a space character or a 0 (zero character). The default is to pad with spaces. An alternate padding character can be specified by prefixing it with a single quote ('). See the examples below.
3. An optional alignment specifier that says if the result should be left-justified or right-justified. The default is right-justified; a - character here will make it left-justified.
4. An optional number, a width specifier that says how many characters (minimum) this conversion should result in.
5. An optional precision specifier in the form of a period (`.') followed by an optional decimal digit string that says how many decimal digits should be displayed for floating-point numbers. When using this specifier on a string, it acts as a cutoff point, setting a maximum character limit to the string.

6. A type specifier that says what type the argument data should be treated as. Possible types:

   • % - 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.
   • e - the argument is treated as scientific notation (e.g. 1.2e+2). The precision specifier stands for the number of digits after the decimal point since PHP 5.2.1. In earlier versions, it was taken as number of significant digits (one less).
   • E - like %e but uses uppercase letter (e.g. 1.2E+2).
   • 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 (locale aware).
   • F - the argument is treated as a float, and presented as a floating-point number (non-locale aware). Available since PHP 4.3.10 and PHP 5.0.3.
   • g - shorter of %e and %f.
   • G - shorter of %E and %f.
   • o - 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).

The format string supports argument numbering/swapping. Here is an example:

Example #1 Argument swapping

<?php
$num = 5;
$location = 'tree';

$format = 'There are %d monkeys in the %s';
printf($format, $num, $location);
?> This will output "There are 5 monkeys in the tree". But imagine we are creating a format string in a separate file, commonly because we would like to internationalize it and we rewrite it as:

Example #2 Argument swapping

<?php
$format = 'The %s contains %d monkeys';
printf($format, $num, $location);
?> We now have a problem. The order of the placeholders in the format string does not match the order of the arguments in the code. We would like to leave the code as is and simply indicate in the format string which arguments the placeholders refer to. We would write the format string like this instead:

Example #3 Argument swapping

<?php
$format = 'The %2$s contains %1$d monkeys';
printf($format, $num, $location);
?> An added benefit here is that you can repeat the placeholders without adding more arguments in the code. For example:

Example #4 Argument swapping

<?php
$format = 'The %2$s contains %1$d monkeys.
           That's a nice %2$s full of %1$d monkeys.';
printf($format, $num, $location);
?> When using argument swapping, the n$ position specifier must come immediately after the percent sign (%), before any other specifiers, as shown in the example below.

Example #5 Position specifier with other specifiers

<?php
$format= 'The %2$s contains %1$04d monkeys';
printf($format, $num, $location);
?>

以上例程会输出：

The tree contains 0005 monkeys

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