- 2.1 Representing Ordinary Strings
- 2.2 Representing Strings with Alternate Notations
- 2.3 Using Here-Documents
- 2.4 Finding the Length of a String
- 2.5 Processing a Line at a Time
- 2.6 Processing a Byte at a Time
- 2.7 Performing Specialized String Comparisons
- 2.8 Tokenizing a String
- 2.9 Formatting a String
- 2.10 Using Strings As IO Objects
- 2.11 Controlling Uppercase and Lowercase
- 2.12 Accessing and Assigning Substrings
- 2.13 Substituting in Strings
- 2.14 Searching a String
- 2.15 Converting Between Characters and ASCII Codes
- 2.16 Implicit and Explicit Conversion
- 2.17 Appending an Item Onto a String
- 2.18 Removing Trailing Newlines and Other Characters
- 2.19 Trimming Whitespace from a String
- 2.20 Repeating Strings
- 2.21 Embedding Expressions Within Strings
- 2.22 Delayed Interpolation of Strings
- 2.23 Parsing Comma-Separated Data
- 2.24 Converting Strings to Numbers (Decimal and Otherwise)
- 2.25 Encoding and Decoding rot13 Text
- 2.26 Encrypting Strings
- 2.27 Compressing Strings
- 2.28 Counting Characters in Strings
- 2.29 Reversing a String
- 2.30 Removing Duplicate Characters
- 2.31 Removing Specific Characters
- 2.32 Printing Special Characters
- 2.33 Generating Successive Strings
- 2.34 Calculating a 32-Bit CRC
- 2.35 Calculating the MD5 Hash of a String
- 2.36 Calculating the Levenshtein Distance Between Two Strings
- 2.37 Encoding and Decoding base64 Strings
- 2.38 Encoding and Decoding Strings (uuencode/uudecode)
- 2.39 Expanding and Compressing Tab Characters
- 2.40 Wrapping Lines of Text
- 2.41 Conclusion
This chapter is from the book
This chapter is from the book
This chapter is from the book
2.24 Converting Strings to Numbers (Decimal and Otherwise)
Basically there are two ways to convert strings to numbers: the Kernel method Integer and Float and the to_i and to_f methods of String. (Capitalized method names such as Integer are usually reserved for special data conversion functions like this.)
The simple case is trivial, and these are equivalent:
x = "123".to_i # 123
y = Integer("123") # 123
When a string is not a valid number, however, their behaviors differ:
x = "junk".to_i # silently returns 0
y = Integer("junk") # error
to_i stops converting when it reaches a non-numeric character, but Integer raises an error:
x = "123junk".to_i # 123
y = Integer("123junk") # error
Both allow leading and trailing whitespace:
x = " 123 ".to_i # 123
y = Integer(" 123 ") # 123
Floating point conversion works much the same way:
x = "3.1416".to_f # 3.1416
y = Float("2.718") # 2.718
Both conversion methods honor scientific notation:
x = Float("6.02e23") # 6.02e23
y = "2.9979246e5".to_f # 299792.46
to_i and Integer also differ in how they handle different bases. The default, of course, is decimal or base ten; but we can work in other bases also. (The same is not true for floating point.)
When talking about converting between numeric bases, strings always are involved. After all, an integer is an integer, and they are all stored in binary.
Base conversion, therefore, always means converting to or from some kind of string. Here we're looking at converting from a string. (For the reverse, see section 5.18 "Performing Base Conversions" and section 5.5 "Formatting Numbers for Output.")
When a number appears in program text as a literal numeric constant, it may have a "tag" in front of it to indicate base. These tags are 0b for binary, a simple 0 for octal, and 0x for hexadecimal.
These tags are honored by the Integer method but not by the to_i method:
x = Integer("0b111") # binary - returns 7
y = Integer("0111") # octal - returns 73
z = Integer("0x111") # hexadecimal - returns 291
x = "0b111".to_i # 0
y = "0111".to_i # 0
z = "0x111".to_i # 0
to_i, however, allows an optional second parameter to indicate base. Typically, the only meaningful values are 2, 8, 10 (the default), and 16. However, tags are not recognized even with the base parameter.
x = "111".to_i(2) # 7 y = "111".to_i(8) # octal - returns 73 z = "111".to_i(16) # hexadecimal - returns 291 x = "0b111".to_i # 0 y = "0111".to_i # 0 z = "0x111".to_i # 0
Because of the "standard" behavior of these methods, a digit that is inappropriate for the given base will be treated differently:
x = "12389".to_i(8) # 123 (8 is ignored)
y = Integer("012389") # error (8 is illegal)
Although it might be of limited usefulness, to_i handles bases up to 36, using all letters of the alphabet. (This may remind you of the base64 encoding; for information on that, see section 2.37, "Encoding and Decoding base64 Strings.")
x = "123".to_i(5) # 66 y = "ruby".to_i(36) # 1299022
It's also possible to use the scanf standard library to convert character strings to numbers. This library adds a scanf method to Kernel, to IO, and to String:
str = "234 234 234"
x, y, z = str.scanf("%d %o %x") # 234, 156, 564
The scanf methods implement all the meaningful functionality of their C counterparts scanf, sscanf, and fscanf. It does not handle binary.