Strings and Data

ABSTRACT

This chapter bridge the gap between abstract data types and their binary reality. We explore how C manages text through memory addresses, the pitfalls of signed data types, and the bitwise logic required to decode modern international text standards like UTF-8.

1. Bit-Level Foundations

Before handling strings, we must master the manipulation of individual bits.

• Bitwise Operators Review: Mastering AND (&), OR (|), XOR (^), and Bit-Shifting (<<, >>) to isolate or combine data.
• Signed vs Unsigned Numbers: Understanding Two’s Complement and how the most significant bit changes the numerical interpretation of a byte.
• Signedness and Bit Masks: Why char can be dangerous in comparisons and how to use unsigned char and masks to ensure logic remains consistent.

2. Memory and Strings

How C manages sequences of characters on the Stack.

• String Concatenation and Memory: Managing the Null Terminator (\0), calculating buffer sizes, and why returning local arrays leads to “Dangling Pointers.”
• Out Parameter: Learning the pattern of passing a destination buffer into a function rather than returning a new one.

3. Internationalization (Unicode)

Moving beyond the 128-character limit of ASCII into the global standard of UTF-8.

• Unicode and UTF-8 Encoding: Understanding variable-width encoding. How a single “symbol” can span 1 to 4 bytes depending on its header bits.
• UTF-8 Codepoint: The math of decoding. Stripping structural header bits and shifting payload bits to reconstruct a character’s unique Unicode identity.

4. Practical Application: String Inspection

Tools and techniques for seeing what is actually inside a string variable.

• Format Specifiers: Using %p for addresses, %hhb for binary, and %hhu for unsigned byte values.
• Decoding Logic: implementing get_size_of_symbol and codepoint_of to navigate multi-byte strings correctly.

Quick Reference: UTF-8 Header Patterns