String Formatting
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The order for string formatting is
%[flags][width][.precision]specifier
%[flags][width][.precision]specifier
string.format(formatstring, ...)
String formatting is used, well, to format strings. This is done through the string.format function; something that requires specific instructions. These instructions follow the format %[flags][width][.precision]specifier. string.format accepts unlimited arguments.
Specifiers
The most important part of string formatting is the specifiers:
| Specifier | Accepts | Outputs | Example |
|---|---|---|---|
| c | integer | corresponding ASCII character | 3 |
| d or i | integer | decimal representation | 321 |
| e/E | float | scientific notation using lowercase e/E | 3.296e2/3.296E2 |
| f | float | 3231.1231 | |
| g/G | float | The shorter of e/E and f | 3E14/3e14 |
| o | integer | octal representation | 610 |
| q | string | Formats a string in a form suitable to be safely read back by the Lua interpreter: the string is written between double quotes, and all double quotes, newlines, embedded zeros, and backslashes in the string are correctly escaped when written. | "print(\"Hi\")" |
| s | string | Hello, World! | |
| u | positive integer | decimal representation | 3131 |
| x/X | integer | Hexadecimal representation | 7fa/7FA |
| % | A % followed by another % will return the % sign itself | % |
Examples
Flags and Width
| Flag | Description |
|---|---|
| - | Left-justify the given field width. Right justification is the default (see width below) |
| + | Forces to precede by a + or - sign, even if the number is positive. The default only shows the - sign in front of a negative number. |
| (space) | A blank space is inserted before the value |
| # | Used with o and x/X, writes a 0 (octal) or 0x/0X (hex) before the values for values other than zero. Used with e/E and f, it forces the written output to contain a decimal point even if no digits would follow. By default, if no digits follow, no decimal point is written. Used with g or G the result is the same as with e or E but trailing zeros are not removed. |
| 0 | Left-pads the number with 0s instead of empty spaces (see width below) |
| width | Description |
|---|---|
| (number) | Minimum number of characters to return. If the number of characters to be formatted is less than this number, then the result is padded with blank spaces. Otherwise, nothing happens. |
Example
print(string.format("%-10d", 300))
Output:
300 -- There are 7 spaces there. I counted :D
print(string.format("%+i is less than %i", 300, 3000)) -- First %i for the second argument, second %i for the third
Output:
+300 is less than 3000
print(string.format("You can declare a hexadecimal number by starting it with 0x, like this: %#x.", 1))
Output:
You can declare a hexadecimal number by starting it with 0x, like this: 0x1.
print(string.format("There is a% i%% chance of rain in Seattle, today.", 300))
Output:
There is a 300% chance of rain in Seattle, today.
print(string.format("%012i", 300))
Output:
000000000300
Precision
| .precision | Description |
|---|---|
| .number | For integer specifiers (d, i, o, u, x/X): precision specifies the minimum number of digits to be returned. If the value to be formatted is shorter than this number, the result is padded with leading zeros. A precision of 0 means that no character is written for the value 0. For e/E and f specifiers: this is the number of digits to be printed after the decimal point. For g/G specifiers: This is the maximum number of digits (before the e/E, if present). For s: this is the maximum number of characters to be returned. For c and q types: it has no effect. When no precision is specified, the default is 1. If the period is given without a value for precision, 0 is assumed. |
Example
print(string.format("%012.3E", 301141))
-- Pad it with 0s to make sure there are 12 digits, put 3 numbers before the E, and return it in scientific notation
Output:
0003.011E+05
print(string.format("string.format > string.sub. %.3s", "Harry Potter trolls!")) -- return first 3 letters of the string
Output:
string.format > string.sub. Har
print(string.format("Once upon a time, there was a magic pony named %s, it had %i horns, and it's location in RAM was %#.9x.", "dap300", 0, 10000000000))
Output:
Once upon a time, there was a magic pony named dap300, it had 0 horns, and it's location in RAM was 0x2540be400.
