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docs: clear notes and add examples
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‎.gitignore‎

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/.idea/editor.xml
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/.idea/misc.xml
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/.idea/vcs.xml
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# TODO: how to ignore executables WITHOUT extension?

‎reference_to_md/cpp/keywords.md‎

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‎reference_to_md/cpp/language/examples/name/README.md‎

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# _identifier_
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## := 💡sequence of digits + underscores, lowercase and uppercase Latin letters + MOST Unicode characters💡
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* [example.cpp](example.cpp)
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## requirements

‎reference_to_md/cpp/language/examples/name/example.cpp‎

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#include <iostream>
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int main() {
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// 1. with Latin letters
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int myVariable = 10;
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// 2. case-sensitive
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int MyVariable = 20;
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int MYVARIABLE = 30; // MYVARIABLE != MyVariable
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std::cout << "myVariable: " << myVariable << std::endl;
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std::cout << "MyVariable: " << MyVariable << std::endl;
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std::cout << "MYVARIABLE: " << MYVARIABLE << std::endl;
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// 3. with underscores (`_`)
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int my_variable = 40;
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int _private = 50;
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int __double_underscore = 60;
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std::cout << "my_variable: " << my_variable << std::endl;
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std::cout << "_private: " << _private << std::endl;
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// 4. with digits (NEVER as start)
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int var1 = 70;
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int variable123 = 80;
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int var_2_test = 90;
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// int 1var = 100; // ❌ ERROR: cannot start with digit
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std::cout << "var1: " << var1 << std::endl;
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std::cout << "variable123: " << variable123 << std::endl;
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// 5. arbitrarily long identifiers (every character is significant)
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int thisIsAVeryLongIdentifierNameThatIsStillValidInCppAndEveryCharacterMatter = 110;
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std::cout << "Long identifier 0: " << thisIsAVeryLongIdentifierNameThatIsStillValidInCppAndEveryCharacterMatter << std::endl;
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// 6. MOST Unicode characters are ALLOWED (implementation-dependent)
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// Common Unicode characters / USUALLY work:
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// - Latin extended characters
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// - Greek letters
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// - Some mathematical symbols
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// those / may NOT compile | ALL systems
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// int café = 120; // Latin extended
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// int α = 130; // Greek alpha
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// int β = 140; // Greek beta
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// Unicode / characters are NOT ALLOWED
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// int 你好 = 150; // ❌ May not work
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// int 😀 = 160; // ❌ Emojis are NOT allowed
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// int ∑ = 170; // ❌ Many mathematical symbols are NOT allowed
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// 7. EVERY character is significant
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int temp = 300;
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int temp_ = 310;
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int _temp = 320;
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int temp1 = 330;
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int temp_1 = 340;
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std::cout << "temp: " << temp << std::endl;
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std::cout << "temp_: " << temp_ << std::endl;
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std::cout << "_temp: " << _temp << std::endl;
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std::cout << "temp1: " << temp1 << std::endl;
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std::cout << "temp_1: " << temp_1 << std::endl;
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return 0;
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}

‎reference_to_md/cpp/language/name.md‎

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An _identifier_ is an arbitrarily long sequence of digits, underscores, lowercase and uppercase Latin letters, and most Unicode characters.
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The first character of a valid identifier must be one of the following:
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* uppercase Latin letters A-Z
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* lowercase Latin letters a-z
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* underscore
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* any Unicode character with the Unicode property [XID_Start](https://www.unicode.org/reports/tr31/#Table_Lexical_Classes_for_Identifiers)
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Any other character of a valid identifier must be one of the following:
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* digits 0-9
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* uppercase Latin letters A-Z
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* lowercase Latin letters a-z
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* underscore
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* any Unicode character with the Unicode property [XID_Continue](https://www.unicode.org/reports/tr31/#Table_Lexical_Classes_for_Identifiers)
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The lists of characters with properties XID_Start and XID_Continue can be found in [DerivedCoreProperties.txt](https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt).
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Identifiers are case-sensitive (lowercase and uppercase letters are distinct), and every character is significant. Every identifier must conform to [Normalization Form C](https://www.unicode.org/charts/normalization/).
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Note: Support of Unicode identifiers is limited in most implementations, e.g. [gcc (until 10)](https://gcc.gnu.org/wiki/FAQ#What_is_the_status_of_adding_the_UTF-8_support_for_identifier_names_in_GCC.3F).
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* _identifier_
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* := 💡sequence of digits + underscores, lowercase and uppercase Latin letters + MOST Unicode characters💡
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* arbitrarily long
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* case-sensitive
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* == lowercase letterS != uppercase letters
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* every character is significant
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* MOST Unicode characters
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* ❌!= ALL Unicode characters❌
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* == limited | MOST implementations
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* _Example:_ [gcc 10-](https://gcc.gnu.org/wiki/FAQ#What_is_the_status_of_adding_the_UTF-8_support_for_identifier_names_in_GCC.3F)
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* ⚠️requirements⚠️
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* MUST conform to [Normalization Form C](https://www.unicode.org/charts/normalization/)
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* first character MUST be one of
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* uppercase Latin letters A-Z
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* lowercase Latin letters a-z
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* underscore
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* any Unicode character / 's property [XID_Start](https://www.unicode.org/reports/tr31/#Table_Lexical_Classes_for_Identifiers)
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* _Example:_ [DerivedCoreProperties.txt](https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt)
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* any other character MUST be one of
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* digits 0-9
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* uppercase Latin letters A-Z
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* lowercase Latin letters a-z
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* underscore
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* any Unicode character / 's property [XID_Continue](https://www.unicode.org/reports/tr31/#Table_Lexical_Classes_for_Identifiers)
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* _Example:_ [DerivedCoreProperties.txt](https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt)
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## Contents
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### In declarations
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An identifier can be used [to name](declarations.html "cpp/language/declarations") objects, references, functions, enumerators, types, class members, namespaces, templates, template specializations, parameter packs(since C++11), goto labels, and other entities, with the following exceptions:
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An identifier can be used [to name](declarations.md) objects, references, functions, enumerators, types, class members, namespaces, templates, template specializations, parameter packs(since C++11), goto labels, and other entities, with the following exceptions:
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* The identifiers that are [keywords](../keywords.html "cpp/keyword") cannot be used for other purposes.
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‎reference_to_md/cpp/preprocessor/examples/replace/README.md‎

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# syntax

‎reference_to_md/cpp/preprocessor/examples/replace/syntax.cpp‎

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#include <iostream>
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#include <string>
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using namespace std;
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// ============================================================================
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// (1) Object-like macros: #define identifier replacement-list
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// ============================================================================
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#define PI 3.14159
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#define MAX_SIZE 100
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#define VERSION "1.0.0"
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#define EMPTY // replacement-list is optional (empty)
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void example1_object_like() {
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cout << "\n=== (1) Object-like macros ===\n";
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cout << "PI = " << PI << "\n";
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cout << "MAX_SIZE = " << MAX_SIZE << "\n";
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cout << "VERSION = " << VERSION << "\n";
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// EMPTY expands to nothing
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}
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// ============================================================================
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// (2) Function-like macros: #define identifier(parameters) replacement-list
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// ============================================================================
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#define SQUARE(x) ((x) * (x))
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#define MAX(a, b) ((a) > (b) ? (a) : (b))
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#define MIN(a, b) ((a) < (b) ? (a) : (b))
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void example2_function_like() {
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cout << "\n=== (2) Function-like macros ===\n";
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cout << "SQUARE(5) = " << SQUARE(5) << "\n"; // 25
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cout << "MAX(10, 20) = " << MAX(10, 20) << "\n"; // 20
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cout << "MIN(10, 20) = " << MIN(10, 20) << "\n"; // 10
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}
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// ============================================================================
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// (3) Variadic macros: #define identifier(parameters, ...) replacement-list
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// C++11 - variable number of arguments
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// ============================================================================
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#define PRINT_NUMS(first, ...) \
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cout << "First: " << first << ", Rest: " << #__VA_ARGS__ << "\n"
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#define LOG(level, msg) \
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cout << "[" << level << "] " << msg << "\n"
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void example3_variadic_with_params() {
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cout << "\n=== (3) Variadic macros (parameters, ...) ===\n";
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PRINT_NUMS(1, 2, 3, 4);
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LOG("INFO", "Server started");
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LOG("ERROR", "Connection failed");
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}
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// ============================================================================
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// (4) Variadic macros: #define identifier(...) replacement-list
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// C++11 - only variadic arguments, no fixed parameters
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// ============================================================================
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#define PRINT_ALL(...) \
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cout << "Arguments: " << #__VA_ARGS__ << "\n"
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#define DEBUG(msg) \
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cout << "[DEBUG] " << msg << "\n"
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void example4_variadic_only() {
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cout << "\n=== (4) Variadic macros (...) only ===\n";
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PRINT_ALL(1, 2, 3);
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PRINT_ALL("hello", "world");
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DEBUG("Some debug message");
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}
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// ============================================================================
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// (5) #undef directive
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// ============================================================================
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#define TEMP_VALUE 999
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void example5_undef() {
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cout << "\n=== (5) #undef directive ===\n";
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cout << "TEMP_VALUE before undef: " << TEMP_VALUE << "\n";
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#undef TEMP_VALUE
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// TEMP_VALUE is now undefined, cannot use it anymore
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// cout << TEMP_VALUE; // ERROR: TEMP_VALUE not defined
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cout << "TEMP_VALUE has been undefined\n";
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}
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// ============================================================================
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// OPERATORS: # (stringification) and ## (token pasting)
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// ============================================================================
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// # operator: converts parameter to string
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#define STRINGIFY(x) #x
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#define TO_STRING(x) STRINGIFY(x)
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// ## operator: concatenates tokens
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#define CONCAT(a, b) a##b
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#define VAR_NAME(prefix, suffix) prefix##_##suffix
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void example6_operators() {
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cout << "\n=== # operator (stringification) ===\n";
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cout << STRINGIFY(hello world) << "\n"; // "hello world"
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cout << TO_STRING(100) << "\n"; // "100"
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cout << "\n=== ## operator (token pasting) ===\n";
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int value_123 = 456;
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cout << "CONCAT(value_, 123) = " << CONCAT(value_, 123) << "\n"; // 456
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int my_variable = 789;
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cout << "VAR_NAME(my, variable) = " << VAR_NAME(my, variable) << "\n"; // 789
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}
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// ============================================================================
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// C++20: __VA_OPT__
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// ============================================================================
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#if __cplusplus >= 202002L
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#define LOG_WITH_COMMA(msg, ...) \
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cout << msg __VA_OPT__(,) __VA_ARGS__ << "\n"
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void example7_va_opt() {
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cout << "\n=== C++20: __VA_OPT__ ===\n";
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LOG_WITH_COMMA("Message"); // No comma if no args
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LOG_WITH_COMMA("Message", " extra"); // Comma if args present
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}
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#endif
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// ============================================================================
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// Scanning and Replacement example
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// ============================================================================
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#define EXAMPLE_SCAN 42
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#define USE_EXAMPLE EXAMPLE_SCAN
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void example8_scanning() {
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cout << "\n=== Scanning and Replacement ===\n";
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cout << "USE_EXAMPLE = " << USE_EXAMPLE << "\n"; // 42
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// Macro expansion: USE_EXAMPLE -> EXAMPLE_SCAN -> 42
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}
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// ============================================================================
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// MAIN
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// ============================================================================
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int main() {
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cout << "=================================================\n";
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cout << " #define SYNTAX EXAMPLES\n";
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cout << "=================================================\n";
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example1_object_like();
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example2_function_like();
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example3_variadic_with_params();
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example4_variadic_only();
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example5_undef();
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example6_operators();
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#if __cplusplus >= 202002L
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example7_va_opt();
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#else
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cout << "\n=== C++20: __VA_OPT__ ===\n";
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cout << "(Requires C++20 or later)\n";
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#endif
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example8_scanning();
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cout << "\n=================================================\n";
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cout << "Summary:\n";
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cout << "(1) Object-like: #define NAME value\n";
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cout << "(2) Function-like: #define NAME(params) replacement\n";
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cout << "(3) Variadic: #define NAME(params, ...) __VA_ARGS__\n";
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cout << "(4) Variadic only: #define NAME(...) __VA_ARGS__\n";
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cout << "(5) Undefine: #undef NAME\n";
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cout << "Operators: # (stringify), ## (concatenate)\n";
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cout << "=================================================\n";
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return 0;
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}

‎reference_to_md/cpp/preprocessor/replace.md‎

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* preprocessor
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* supports
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* text macro replacement
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* function-like text macro replacement
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* [text macro replacement](#object-like-macros)
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* [function-like text macro replacement ](#function-like-macros)
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## Contents
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* [7 See also](replace.html#See_also)
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### Syntax
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* [`identifier`](../language/name.md)
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#### (1)
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* `#define identifier replacement-list`
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* `replacement-list`
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#### Reserved macro names
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A translation unit that [includes a standard library header](../standard_library.html#Including_headers "cpp/standard library") may not #define or #undef names declared in any [standard library header](../headers.html "cpp/header").
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* translation unit /
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* [includes a standard library header](../standard_library.md#including-headers) may NOT `#define` OR `#undef` names / declared | any [standard library header](../headers.md)
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* uses ANY part of the standard library is NOT allowed to `#define` OR `#undef` names lexically identical to
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* [keywords](../keywords.md)
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* [identifiers / special meaning](../keywords.md)
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* | C+11
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* [any standard attribute token](../language/attributes.md#standard-attributes)
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* | C+11
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* EXCEPT TO: [`likely`](../language/attributes/likely.md) & [`unlikely`](../language/attributes/likely.md) defined -- as -- function-like macros
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* | C++20
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A translation unit that uses any part of the standard library is not allowed to #define or #undef names lexically identical to:
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* [keywords](../keywords.html "cpp/keyword")
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* [identifiers with special meaning](../keywords.html "cpp/keyword")
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* [any standard attribute token](../language/attributes.html#Standard_attributes "cpp/language/attributes"), except that [`likely`](../language/attributes/likely.html "cpp/language/attributes/likely") and [`unlikely`](../language/attributes/likely.html "cpp/language/attributes/likely") may be defined as function-like macros(since C++20)
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| (since C++11)
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---|---
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Otherwise, the behavior is undefined.
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#### # and ## operators

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