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Jan 24, 2021 20 tweets 17 min read Read on X
#102 The result of an infinite recursion in template instantiation is undefined behavior: eel.is/c++draft/temp.…

godbolt: godbolt.org/z/jh6bsr Image
#103 Referring to any non-static member or base class of an object in the handler for a function-try-block of a
constructor or destructor for that object results in undefined behavior: eel.is/c++draft/excep…

godbolt: godbolt.org/z/6Yzvvc Image
#104 If the token defined is generated as a result of this replacement process or use of
the defined unary operator does not match one of the two specified forms prior to macro replacement, the
behavior is undefined: eel.is/c++draft/cpp.c…

godbolt: godbolt.org/z/xrdfT4 ImageImage
#105 If there are sequences of preprocessing tokens within the list of arguments to a function-like macro
that would otherwise act as preprocessing directives, the behavior is undefined: eel.is/c++draft/cpp.r…

godbolt: godbolt.org/z/6hfxn5 ImageImage
#106 If an invalid character results from using the stringize operator the behavior is undefined: eel.is/c++draft/cpp.s…

godbolt: godbolt.org/z/jsYbqP ImageImage
#107 If an invalid preprocessing token results from using the concat operator the behavior is undefined: eel.is/c++draft/cpp.c…

godbolt: godbolt.org/z/bqxMKe ImageImage
#108 Using 0 or a number greater than 2147483647 is undefined behavior for #line directive: eel.is/c++draft/cpp.l…

godbolt: godbolt.org/z/ccxcvW ImageImage
#109 When using the pptoken variant of the #line directive, If the directive resulting after all replacements does not match one of the two previous forms, the behavior is undefined.: eel.is/c++draft/cpp.l…

godbolt: godbolt.org/z/E5qvaa ImageImage
#110 If any of the pre-defined macro names in [cpp.predefined], or the identifier defined, is the subject of a #define or a #undef preprocessing directive, the behavior is undefined: eel.is/c++draft/cpp.p…

godbolt: godbolt.org/z/vEY5hz ImageImage
#111 Twist on use of indeterminate value causing undefined behavior.

Using an indeterminate value in a return statement causes the whole branch to be ignored and we just use the return statement at the end.

h/t @rep_stosq_void

godbolt: gcc.godbolt.org/z/nrjaa1 Image
#112 Falling off the end of a coroutine function body that does not return void is undefined behavior: eel.is/c++draft/stmt.…

godbolt: godbolt.org/z/5MTcnz Image
#113 Invoking a resumption member function for a coroutine that is not suspended results in undefined behavior: eel.is/c++draft/dcl.f…

godbolt: godbolt.org/z/W4PYfdPh4 Image
#114 Invoking destroy() on a coroutine that is not suspended is undefined behavior: eel.is/c++draft/dcl.f…

godbolt: godbolt.org/z/3sWf3czPs godbolt screen shot of coro...
#115 Calling a function through an expression whose function type is different from the function type of the called function’s definition results in undefined behavior: godbolt.org/z/snjzbh6oc

[expr.call]p6 eel.is/c++draft/expr.… using f_float = int (*)(flo...
#116 If the substitution of template arguments into a requirement would always result in a substitution failure, the program is ill-formed; no diagnostic required: godbolt.org/z/eez98bfT5

[expr.prim.req]p5 eel.is/c++draft/expr.… template<typename T> concep...
#117 If, during parsing, lookup finds that a name in a template argument is bound to (part of) the declaration being parsed, the program is ill-formed. No diagnostic is required: godbolt.org/z/z354fnYGa

[stmt.ambig]p3 eel.is/c++draft/stmt.… #include <iostream> #includ...
#118 If no arguments to a constexpr function allow it to be used in a core constant expression context,
the program is ill-formed, no diagnostic required: godbolt.org/z/MdnsWe69E

[dcl.constexpr]p6 eel.is/c++draft/dcl.c… constexpr int f(bool b) { r...
#119 If no specialization of
the template would satisfy the requirements for a constexpr function when considered as a non-template
function, the template is ill-formed, no diagnostic required: godbolt.org/z/8rMd18rPj

[dcl.constexpr]p7 eel.is/c++draft/dcl.c… template <typename T> struc...
#120 If constinit is applied to any decl of a var, it shall be applied to the initializing decl. No diagnostic is required if no constinit declaration is reachable at the point of the initializing declaration: godbolt.org/z/bWMaTh8Ed

[dcl.constinit]p1 eel.is/c++draft/dcl.c… // Translation unit 1 exter...
#121 Some identifiers are reserved for use by C++ implementations and shall not be used otherwise; no
diagnostic is required: godbolt.org/z/658K4djY3

[lex.name]p3 eel.is/c++draft/lex.n… int _z;  int main() {     i...

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More from @shafikyaghmour

Sep 19, 2021
💯 Cursed code

Same code compiles in both C and C++ and can detect which version of C and C++ with language features alone.

With not be taking questions.

#cplusplus
#programming #if true #define ISC 0 #els...
I have added this to my github "determine_c_or_cpp" repo: github.com/shafik/determi…

Enjoy!
Read 4 tweets
Apr 4, 2021
#114 Invoking destroy() on a coroutine that is not suspended is undefined behavior: eel.is/c++draft/dcl.f…

godbolt: godbolt.org/z/3sWf3czPs godbolt screen shot of coro...
#115 Calling a function through an expression whose function type is different from the function type of the called function’s definition results in undefined behavior: godbolt.org/z/snjzbh6oc

[expr.call]p6 eel.is/c++draft/expr.… using f_float = int (*)(flo...
#116 If the substitution of template arguments into a requirement would always result in a substitution failure, the program is ill-formed; no diagnostic required: godbolt.org/z/eez98bfT5

[expr.prim.req]p5 eel.is/c++draft/expr.… template<typename T> concep...
Read 10 tweets
Sep 18, 2020
Structure and Interpretation of Computer Programs: SICP
By @code_report

Why SICP matters?

#CppCon
#Cplusplus Image
@code_report Pascal is for building pyramids

Lisp is for building organisms Image
@code_report "We write awful code" Image
Read 4 tweets
May 31, 2019
Let’s do this:

One Like, One Undefined Behavior.

I plan on running this through the weekend at least.

#Cplusplus
#Programming
Signed integer overflow/underflow is undefined behavior

int x1=std::numeric_limits<int>::max()+1;
int x2=std::numeric_limits<int>::min()-1;

[expr.pre]p4 eel.is/c++draft/expr#…

godbolt: godbolt.org/z/Ga-fbb
#2 Signed integer overflow/underflow is undefined behavior 2

int x3=std::numeric_limits<int>::min() / -1;

[expr.pre]p4 eel.is/c++draft/expr#…

godbolt: godbolt.org/z/ytC8oi
Read 65 tweets

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