235 lines
14 KiB
Markdown
Vendored
235 lines
14 KiB
Markdown
Vendored
# mruby-sprintf
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This mrbgem provides `sprintf` functionality for mruby. It allows you to format strings according to a specified format string, similar to the `sprintf` function in C or other languages.
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## Functionality
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- Provides the `sprintf` kernel function.
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- Adds the `%` operator to the `String` class as an alias for `sprintf`.
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## Usage
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You can use `sprintf` or the `String#%` operator for string formatting:
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```ruby
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# Using sprintf
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str = sprintf("Hello, %s! You are %d years old.", "World", 30)
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puts str # Output: Hello, World! You are 30 years old.
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# Using String#%
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str2 = "The value is %.2f" % 12.3456
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puts str2 # Output: The value is 12.35
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# Using String#% with an array of arguments
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str3 = "%d + %d = %d" % [1, 2, 1+2]
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puts str3 # Output: 1 + 2 = 3
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```
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## Format Specifiers
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This mrbgem supports a wide range of format specifiers, flags, width, and precision options. For a comprehensive list and detailed explanation of all supported format specifiers and their behavior, please refer to the extensive comments within the C source file: [`src/sprintf.c`](src/sprintf.c).
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## Format Specifiers Details
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The `sprintf` function in this mrbgem supports a variety of field type characters that control how arguments are interpreted and formatted.
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### Integer Formats
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| Field | Description |
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| :---- | :---------------------------------------------------------------------------------------------------------------------- |
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| `b` | Convert argument as a binary number. Negative numbers will be displayed as a two's complement prefixed with `..1`. |
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| `B` | Equivalent to `b`, but uses an uppercase `0B` for prefix in the alternative format (when `#` flag is used). |
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| `d` | Convert argument as a decimal number. |
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| `i` | Identical to `d`. |
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| `o` | Convert argument as an octal number. Negative numbers will be displayed as a two's complement prefixed with `..7`. |
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| `u` | Identical to `d`. (In many `sprintf` implementations, `u` is for unsigned decimal, but here it behaves like `d`). |
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| `x` | Convert argument as a hexadecimal number. Negative numbers will be displayed as a two's complement prefixed with `..f`. |
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| `X` | Equivalent to `x`, but uses uppercase letters for hexadecimal digits (e.g., `0XFF` vs `0xff`). |
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### Float Formats
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| Field | Description |
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| :---- | :------------------------------------------------------------------------------------------------------------------------------------------------------ |
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| `e` | Convert floating-point argument into exponential notation (e.g., `[-]d.dddddde[+-]dd`). Precision specifies digits after the decimal point (default 6). |
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| `E` | Equivalent to `e`, but uses an uppercase `E` for the exponent. |
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| `f` | Convert floating-point argument as `[-]ddd.dddddd`. Precision specifies digits after the decimal point. |
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| `g` | Converts a floating-point number using `e` or `f` form based on exponent and precision. Precision specifies significant digits. |
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| `G` | Equivalent to `g`, but uses an uppercase `E` in exponent form if applicable. |
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### Other Formats
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| Field | Description |
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| :---- | :-------------------------------------------------------------------------------------------------------------- |
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| `c` | Argument is treated as the numeric code for a single character or a single character string itself. |
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| `p` | Argument's `inspect` method is called, and the result is substituted. |
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| `s` | Argument is a string to be substituted. If precision is specified, at most that many characters will be copied. |
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| `%` | A literal percent sign (`%`) itself will be displayed. No argument is taken. |
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### Flags
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Flags modify the behavior of the format specifiers:
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| Flag | Applies to | Meaning |
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| :--------- | :---------------------------------- | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| `space` | Numeric Formats (bBdiouxX, aAeEfgG) | Leave a space at the start of non-negative numbers. For `o`, `x`, `X`, `b`, `B`, uses a minus sign with absolute value for negative values. |
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| `(digit)$` | All | Specifies the absolute argument number for this field (e.g., `%2$d` uses the second argument). Cannot be mixed with relative argument numbers. |
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| `#` | bBoxX, aAeEfgG | Use an alternative format. For `o`, increases precision to make the first digit `0` if not formatted as complement. For `x`, `X`, `b`, `B` (non-zero), prefixes with `0x`, `0X`, `0b`, `0B`. For `e`, `E`, `f`, `g`, `G`, forces a decimal point. For `g`, `G`, do not remove trailing zeros. |
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| `+` | Numeric Formats | Add a leading plus sign (`+`) to non-negative numbers. For `o`, `x`, `X`, `b`, `B`, uses a minus sign with absolute value for negative values. |
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| `-` | All | Left-justify the result of this conversion. |
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| `0` (zero) | Numeric Formats | Pad with zeros, not spaces. For `o`, `x`, `X`, `b`, `B`, radix-1 is used for negative numbers formatted as complements. |
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| `*` | All | Use the next argument as the field width. If negative, left-justifies. If `*` is followed by a number and `$`, use that argument as width (e.g., `%*1$d`). |
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## Further Examples (from C source comments)
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Here are more examples illustrating the use of flags, width, and precision, adapted from the comments in `src/sprintf.c`.
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### Examples of Flags
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```ruby
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# '+' and space flag specifies the sign of non-negative numbers.
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puts sprintf("%d", 123) #=> "123"
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puts sprintf("%+d", 123) #=> "+123"
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puts sprintf("% d", 123) #=> " 123"
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# '#' flag for 'o' increases number of digits to show '0'.
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# '+' and space flag changes format of negative numbers.
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puts sprintf("%o", 123) #=> "173"
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puts sprintf("%#o", 123) #=> "0173"
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puts sprintf("%+o", -123) #=> "-173"
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puts sprintf("%o", -123) #=> "..7605"
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puts sprintf("%#o", -123) #=> "..7605"
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# '#' flag for 'x' add a prefix '0x' for non-zero numbers.
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# '+' and space flag disables complements for negative numbers.
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puts sprintf("%x", 123) #=> "7b"
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puts sprintf("%#x", 123) #=> "0x7b"
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puts sprintf("%+x", -123) #=> "-7b"
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puts sprintf("%x", -123) #=> "..f85"
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puts sprintf("%#x", -123) #=> "0x..f85" # Note: mruby's output might differ slightly for complements with #
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puts sprintf("%#x", 0) #=> "0"
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# '#' for 'X' uses the prefix '0X'.
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puts sprintf("%X", 123) #=> "7B"
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puts sprintf("%#X", 123) #=> "0X7B"
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# '#' flag for 'b' add a prefix '0b' for non-zero numbers.
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# '+' and space flag disables complements for negative numbers.
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puts sprintf("%b", 123) #=> "1111011"
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puts sprintf("%#b", 123) #=> "0b1111011"
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puts sprintf("%+b", -123) #=> "-1111011"
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puts sprintf("%b", -123) #=> "..10000101"
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puts sprintf("%#b", -123) #=> "0b..10000101" # Note: mruby's output might differ slightly for complements with #
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puts sprintf("%#b", 0) #=> "0"
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# '#' for 'B' uses the prefix '0B'.
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puts sprintf("%B", 123) #=> "1111011"
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puts sprintf("%#B", 123) #=> "0B1111011"
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# '#' for 'e' forces to show the decimal point.
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puts sprintf("%.0e", 1) #=> "1e+00"
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puts sprintf("%#.0e", 1) #=> "1.e+00"
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# '#' for 'f' forces to show the decimal point.
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puts sprintf("%.0f", 1234) #=> "1234"
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puts sprintf("%#.0f", 1234) #=> "1234."
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# '#' for 'g' forces to show the decimal point.
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# It also disables stripping lowest zeros.
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puts sprintf("%g", 123.4) #=> "123.4"
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puts sprintf("%#g", 123.4) #=> "123.400"
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puts sprintf("%g", 123456) #=> "123456"
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puts sprintf("%#g", 123456) #=> "123456."
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```
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### Examples of Width
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The width specifies the minimum number of characters that will be written.
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Padding is typically done with spaces, or with zeros if the `0` flag is used.
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```ruby
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# padding is done by spaces, width=20
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# 0 or radix-1. <------------------>
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puts sprintf("%20d", 123) #=> " 123"
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puts sprintf("%+20d", 123) #=> " +123"
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puts sprintf("%020d", 123) #=> "00000000000000000123"
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puts sprintf("%+020d", 123) #=> "+0000000000000000123"
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puts sprintf("% 020d", 123) #=> " 0000000000000000123"
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puts sprintf("%-20d", 123) #=> "123 "
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puts sprintf("%-+20d", 123) #=> "+123 "
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puts sprintf("%- 20d", 123) #=> " 123 "
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puts sprintf("%020x", -123) #=> "..ffffffffffffffff85" # Output for negative hex with 0-padding can vary
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```
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### Examples of Precision
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For numeric fields, precision controls the number of decimal places or minimum number of digits.
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For strings, it determines the maximum number of characters.
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```ruby
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# precision for 'd', 'o', 'x' and 'b' is minimum number of digits
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# <------>
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puts sprintf("%20.8d", 123) #=> " 00000123"
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puts sprintf("%20.8o", 123) #=> " 00000173"
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puts sprintf("%20.8x", 123) #=> " 0000007b"
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puts sprintf("%20.8b", 123) #=> " 01111011"
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puts sprintf("%20.8d", -123) #=> " -00000123"
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puts sprintf("%20.8o", -123) #=> " ..777605" # Complemented output
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puts sprintf("%20.8x", -123) #=> " ..ffff85" # Complemented output
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puts sprintf("%20.8b", -11) #=> " ..110101" # Complemented output
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# "0x" and "0b" for '#x' and '#b' is not counted for precision,
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# but "0" for '#o' is counted. <------>
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puts sprintf("%#20.8d", 123) #=> " 00000123"
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puts sprintf("%#20.8o", 123) #=> " 00000173" # '#' with 'o' and precision
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puts sprintf("%#20.8x", 123) #=> " 0x0000007b"
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puts sprintf("%#20.8b", 123) #=> " 0b01111011"
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puts sprintf("%#20.8d", -123) #=> " -00000123"
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puts sprintf("%#20.8o", -123) #=> " ..777605" # Complemented output
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puts sprintf("%#20.8x", -123) #=> " 0x..ffff85" # Complemented output with #
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puts sprintf("%#20.8b", -11) #=> " 0b..110101" # Complemented output with #
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# precision for 'e' is number of digits after the decimal point
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# <------>
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puts sprintf("%20.8e", 1234.56789) #=> " 1.23456789e+03"
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# precision for 'f' is number of digits after the decimal point
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# <------>
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puts sprintf("%20.8f", 1234.56789) #=> " 1234.56789000"
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# precision for 'g' is number of significant digits
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# <------->
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puts sprintf("%20.8g", 1234.56789) #=> " 1234.5679"
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# <------->
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puts sprintf("%20.8g", 123456789) #=> " 1.2345679e+08"
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# precision for 's' is maximum number of characters
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# <------>
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puts sprintf("%20.8s", "string test") #=> " string t"
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```
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### General Examples
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```ruby
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puts sprintf("%d %04x", 123, 123) #=> "123 007b"
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puts sprintf("%08b '%4s'", 123, 123) #=> "01111011 ' 123'" # Note: mruby output for %s with number might differ
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puts sprintf("%1$*2$s %2$d %1$s", "hello", 8) #=> " hello 8 hello"
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puts sprintf("%1$*2$s %2$d", "hello", -8) #=> "hello -8"
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puts sprintf("%+g:% g:%-g", 1.23, 1.23, 1.23) #=> "+1.23: 1.23:1.23"
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puts sprintf("%u", -123) #=> "-123"
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```
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### Named References
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For more complex formatting, Ruby supports a reference by name.
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`%<name>s` style uses format style, but `%{name}` style doesn't (in standard Ruby, mruby might vary).
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```ruby
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puts sprintf("%<foo>d : %<bar>f", { :foo => 1, :bar => 2.0 }) # Using a float for %f
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#=> "1 : 2.000000"
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# The %{name} style might behave differently or not be supported in the same way as CRuby.
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# Standard CRuby example:
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# puts sprintf("%{foo}f", { :foo => 1 }) # => "1f" (This specific syntax might not apply or work in mruby)
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# For mruby, stick to %<name>type for named arguments:
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puts sprintf("%<foo>s", { :foo => "test" }) #=> "test"
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```
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