C++ Performance Quiz

How well do you know what the compiler does? Pick a question and find out.

• 1. Memory Layout: Array of Structs vs Struct of Arrays

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• 2. Atomic Bit Set: Need Return Value or Not

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• 3. Atomic Increment Ordering: relaxed vs. seq_cst

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• 4. Atomic Store Ordering: memory_order_release vs memory_order_seq_cst

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• 5. Lambda Capture: Value Capture vs Reference Capture

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• 6. Atomic Counter Updates: Per-Operation vs Batched Flush

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• 7. Sorted Array Search: std::lower_bound vs. Linear Scan

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• 8. Packed Bit Storage: Bit Fields vs Manual Bit Masking

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• 9. Power-of-Two Indexing: Bitwise AND vs operator%

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• 10. Bit Counting: Manual Loop vs std::popcount

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• 11. Hash Map Lookup: Bloom Filter Precheck vs Direct Lookup

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• 12. Boolean Short-Circuit: Cheap-Then-Expensive vs Expensive-Then-Cheap

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• 13. Conditional Write: Two Control-Flow Styles

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• 14. Aliasing Model: char* vs char8_t* Stores

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• 15. Lookup Table: Static Array vs. Stack Array

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• 16. Dense Integer Keys: Counting Sort vs std::sort

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• 17. Membership Checks: Dense Bitset vs Sparse Hash Set

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• 18. Integer Division: Compile-Time Constant vs. Runtime Variable

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• 19. Type Check in Hot Loop: dynamic_cast vs Explicit Tag

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• 20. std::vector Insertion: emplace_back vs push_back

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• 21. Removing Elements from a Vector: Two Approaches

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• 22. Error Handling Under Frequent Failures: Exception vs Error Code

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• 23. Cache Coherency: Packed vs Padded Thread Counters

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• 24. Free Function vs. Member Function

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• 25. Float Parsing: std::from_chars vs strtod

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• 26. API Shape: hasFailure vs hasValue

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• 27. Read-Heavy Map Lookup: unordered_map vs. Sorted Vector + Binary Search

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• 28. Map String Lookup: Two Key-Passing Styles

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• 29. Struct Layout: Combined vs Split Field Storage

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• 30. Bounded Buffer: inplace_vector vs std::vector

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• 31. Division by Constant: Integer vs Float Path

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• 32. Lambda Closure Performance in a Tight Loop

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• 33. Branch Annotation Direction: [[likely]] vs [[unlikely]]

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• 34. Searching Sorted Data: Linear Search vs Binary Search

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• 35. Container Iteration: std::list vs std::vector

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• 36. std::list Traversal: Forward vs Two-Ended

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• 37. Access Pattern: Function-local static vs Global

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• 38. Character Lower-casing: Locale-aware vs Lookup Table

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• 39. Loop-Carried Dependency: Single vs Split Accumulator

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• 40. Shared Pointer Creation: new vs make_shared

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• 41. Unique Pointer Array Init: Default vs Value Initialisation

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• 42. Map Lookup: find() vs. count() + at()

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• 43. Sorted Map Insertion: Hint vs No Hint

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• 44. Key Lookup: std::map vs std::unordered_map

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• 45. 2D Array Traversal: Row-Major vs Column-Major

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• 46. Memory Allocation: Object Pool vs Repeated new/delete

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• 47. Return Paths and NRVO: Single Local vs Multiple Locals

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• 48. Thread-Safe Counter: Two Synchronization Approaches

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• 49. std::vector Reallocation: noexcept Move Constructor

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• 50. Returning a Named Local: Plain Return vs std::move Return

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• 51. Median Selection: nth_element vs Full Sort

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• 52. One-Time Initialization: std::call_once vs Function-Local static

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• 53. Returning std::optional<Result>: Wrapper Local vs Value Local

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• 54. Top-K Selection: partial_sort vs Full Sort

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• 55. Single-Threaded Counter: Plain int vs std::atomic

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• 56. Top Element Maintenance: Priority Queue vs Sorted Insert

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• 57. Range-based for loop: copy vs reference

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• 58. std::regex: Function-Local vs. Static-Local Declaration

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• 59. std::vector Growth: reserve Before push_back vs Without

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• 60. std::vector Pre-allocation: reserve vs resize

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• 61. Small-Collection Membership: std::set vs std::unordered_set

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• 62. Shared Counter Under Contention: Sharded vs Single Atomic

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• 63. Range Loop Over shared_ptr: By-Value vs By-Reference Variable

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• 64. Smart Pointer Move: shared_ptr Copy vs. unique_ptr Move

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• 65. std::function with Large Objects: Two Capture Strategies

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• 66. std::string: Tokenization and Small String Optimization

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• 67. std::sort Comparator: Function Pointer vs Lambda

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• 68. Branch Prediction: Sorted vs. Shuffled Data

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• 69. SSE Multiply: Scalar Lane vs Packed Lanes

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• 70. Buffer Allocation: Heap Buffer vs Stack Buffer

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• 71. std::any Storage: Small Object vs Heap-backed Large Object

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• 72. Buffer Equality: std::equal vs std::memcmp

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• 73. Buffer Zero-Initialization: std::fill vs. memset

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• 74. Callback Dispatch: std::function vs Template Parameter

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• 75. Two-Word Readback Patterns

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• 76. Copy vs Move Semantics: std::string Performance

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• 77. Integer-to-String Conversion: std::to_string vs std::to_chars

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• 78. String Building: Two Concatenation Styles

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• 79. String Building: operator+ in Loop vs reserve+append

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• 80. Integer Parsing: atoi vs. std::from_chars

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• 81. Substring Extraction: Owning String vs String View

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• 82. Copying a Short String into a Large Buffer

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• 83. Struct Field Ordering and Implicit Padding

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• 84. Structured Binding: Copy vs Reference

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• 85. Dense Integer Dispatch: switch vs. Function-Pointer Table

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• 86. Tail Recursion Optimization

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• 87. Integer Formatting: std::to_chars vs snprintf

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• 88. Integer-to-String Conversion: std::to_string vs std::format

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• 89. Type Check in Loop: typeid vs Explicit Tag

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• 90. Uncontended Mutex Guard: Inside vs. Outside the Loop Body

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• 91. Hash Lookup Tuning: Two Bucket Density Settings

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• 92. Unordered Map Build: No reserve() vs reserve()

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• 93. UTF-8 Code Point Counting: Nibble Table vs Range Checks

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• 94. Polymorphic Dispatch: Virtual Functions vs std::variant

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• 95. Boolean Vector Storage: std::vector<bool> vs std::vector<uint8_t>

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• 96. Removing a Vector Element: Stable vs Swap Removal

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• 97. Element Storage: Pointer-Owned vs Value-Owned Elements

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• 98. Virtual Call Devirtualization: With and Without final

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• 99. Polymorphic Dispatch: Virtual Function vs CRTP

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• 100. Large Stack Buffer: Initialization

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