string.byte()

The string.byte() function retrieves the numeric ASCII (or Unicode) value of a character or a sequence of characters in a string. It is commonly used for encoding, debugging, and understanding character-level data.

Syntax

string.byte(s, start, end_)

Parameters

Return Value

The function returns:

• A single numeric value if only start is provided.
• Multiple numeric values if both start and end_ are provided.

Examples

Example 1: Retrieve a single ASCII value

The function retrieves the ASCII (or Unicode) value of the first character when no start is specified.

print(string.byte("Lua")) 

-- Output: 76 (ASCII for 'L')

Example 2: Retrieve values for a range of characters

The function retrieves values for all characters between the specified start and end_ positions.

local result = {string.byte("Hello, Lua!", 1, 5)}

print(table.concat(result, ", "))

-- Output: 72, 101, 108, 108, 111

Example 3: ASCII for special characters

You can extract numeric values for special characters as well.

print(string.byte("!")) -- Output: 33
print(string.byte("$")) -- Output: 36
print(string.byte("@")) -- Output: 64

Example 4: Extracting the last character's value

By specifying only the start parameter, you can extract the ASCII value of the last character in a string.

local str = "Lua is great!"
print(string.byte(str, #str)) 

-- Output: 33 (ASCII for '!')

Example 5: Decoding a sequence of characters

You can combine string.byte() with a loop to decode every character in a string into its ASCII values.

local str = "Code"
for i = 1, #str do
    print(string.byte(str, i))
end

-- Output:
-- 67 (C)
-- 111 (o)
-- 100 (d)
-- 101 (e)

Example 6: Invalid parameters

When you pass invalid parameters, the function handles them gracefully by returning nil.

print(string.byte("", 1)) -- Output: nil (empty string)
print(string.byte("Hello", 10)) -- Output: nil (out of range)

Use Cases

• Encoding: Convert strings into numeric values for processing or communication.
• Debugging: Analyze strings to understand encoding or detect invalid characters.
• Cryptography: Transform characters into numeric representations for algorithms.

See also

• string.char(): Converts numeric ASCII (or Unicode) values back into their corresponding characters. This is essentially the reverse of string.byte().
• string.sub(): Extracts substrings, which can be combined with string.byte() to analyze or process specific sections of a string.
• string.unpack(): Retrieves structured data from a packed string, which may complement string.byte() when dealing with encoded strings.