Day 38 — Literals, Raw Strings, Unicode, Attributes, Alignment, and thread_local

1. Problem It Solves

C++11 adds notation and metadata for domain values, readable text, encoded strings, compiler-visible intent, memory alignment, and per-thread state. It makes an important constraint visible instead of leaving readers to guess. This lesson keeps only the C++11 core that fits one focused day.

2. Prerequisites

The ideas from Day 37, plus basic variables, functions, and output already introduced.

3. Core Idea

Mental model: C++11 adds notation and metadata for domain values, readable text, encoded strings, compiler-visible intent, memory alignment, and per-thread state. Identify the relevant value or state, who owns it, and whether the rule acts during compilation or execution.

4. Minimal Syntax

2_kb; R"(raw text)"; u8"text"; [[noreturn]]; alignas(16); thread_local int n;

5. How It Works

The example creates a tiny fixed state with no keyboard input.
C++11 or the standard-library contract applies today's rule.
The program prints the important result so it can be checked against the source.

6. Common Mistakes

A UTF-8 string is still a sequence of code units, so byte indexing is not the same as indexing user-perceived characters.

7. When to Use It

Use it when syntax should express units, text, storage constraints, or thread-local state directly.
Avoid it when it hides ownership, lifetime, type, ordering, or cost.

8. Simple Example

One compact program uses a _kb literal, raw path, UTF-8 text, [[noreturn]], alignas/alignof, and a thread_local counter. The .cpp keeps the data fixed and avoids unrelated abstraction.

Complete sample code

Source file

cpp11/38_literals_raw_strings_unicode_attributes_alignment_thread_local/main.cpp

C++

#include <cstddef>
#include <iostream>

constexpr unsigned long long operator"" _kb(unsigned long long value) {
    return value * 1024ULL;
}

thread_local int calls = 0;

struct alignas(16) Block {
    char bytes[16];
};

[[noreturn]] void stop() {
    throw 1;
}

int main() {
    const char* path = R"(C:\ticks\day1)";
    const char* text = u8"Giá";
    ++calls;

    std::cout << "bytes=" << 2_kb << '\n';
    std::cout << "path=" << path << '\n';
    std::cout << "text=" << text << '\n';
    std::cout << "alignment=" << alignof(Block) << " calls=" << calls << '\n';

    try { stop(); } catch (int) { std::cout << "caught\n"; }
}

9. Key Takeaways

The feature is part of the C++11 scope used in this course.
Understand its lifetime, ownership, type, and ordering consequences.
Compile with warnings and prefer the smallest form that makes the rule obvious.

10. Self-Check Questions

Easy — In C++11, what different needs do R"(C:\ticks)", alignas(16), and thread_local int calls address?
Medium — Read the small example described above. What value or state should it print, and which rule produces that result?
Hard — Find and explain the subtle bug in this situation: A UTF-8 string is still a sequence of code units, so byte indexing is not the same as indexing user-perceived characters. What is the smallest C++11-safe correction?

Practice this lesson's cards

#include <cstddef> #include <iostream> constexpr unsigned long long operator"" _kb(unsigned long long value) { return value * 1024ULL; } thread_local int calls = 0; struct alignas(16) Block { char bytes[16]; }; [[noreturn]] void stop() { throw 1; } int main() { const char* path = R"(C:\ticks\day1)"; const char* text = u8"Giá"; ++calls; std::cout << "bytes=" << 2_kb << '\n'; std::cout << "path=" << path << '\n'; std::cout << "text=" << text << '\n'; std::cout << "alignment=" << alignof(Block) << " calls=" << calls << '\n'; try { stop(); } catch (int) { std::cout << "caught\n"; } }

10. Self-Check Questions

Easy — In C++11, what different needs do R"(C:\ticks)", alignas(16), and thread_local int calls address?
Medium — Read the small example described above. What value or state should it print, and which rule produces that result?
Hard — Find and explain the subtle bug in this situation: A UTF-8 string is still a sequence of code units, so byte indexing is not the same as indexing user-perceived characters. What is the smallest C++11-safe correction?