All Undefined Behavior Solutions on Gang of Coders

Total of 64 Undefined Behavior Solutions

Undefined behavior and sequence points

C++Undefined BehaviorC++ FaqSequence Points

What is the strict aliasing rule?

C++CUndefined BehaviorStrict AliasingType Punning

Why are these constructs using pre and post-increment undefined behavior?

CIncrementUndefined BehaviorOperator PrecedenceSequence Points

Undefined, unspecified and implementation-defined behavior

C++CUndefined BehaviorUnspecified BehaviorImplementation Defined-Behavior

Does the C++ standard allow for an uninitialized bool to crash a program?

C++LlvmUndefined BehaviorAbiLlvm Codegen

Is uninitialized local variable the fastest random number generator?

C++CUndefined BehaviorGarbage

Why is f(i = -1, i = -1) undefined behavior?

C++Language LawyerUndefined Behavior

Why is unsigned integer overflow defined behavior but signed integer overflow isn't?

C++CUndefined BehaviorInteger Overflow

Why does this for loop exit on some platforms and not on others?

CDebuggingUndefined BehaviorBuffer Overflow

What are all the common undefined behaviours that a C++ programmer should know about?

C++UndefinedUndefined BehaviorC++ Faq

Why does this loop produce "warning: iteration 3u invokes undefined behavior" and output more than 4 lines?

C++GccUndefined Behavior

In practice, why would different compilers compute different values of int x = ++i + ++i;?

C++Undefined Behavior

Optimizing away a "while(1);" in C++0x

C++LoopsC++11Language LawyerUndefined Behavior

Why does the enhanced GCC 6 optimizer break practical C++ code?

C++GccCompiler OptimizationUndefined Behavior

Accessing inactive union member and undefined behavior?

C++Undefined BehaviorLanguage LawyerUnions

Why does integer overflow on x86 with GCC cause an infinite loop?

C++CGccX86Undefined Behavior

When does invoking a member function on a null instance result in undefined behavior?

C++Undefined BehaviorLanguage LawyerStandards ComplianceNull Pointer

Is the "struct hack" technically undefined behavior?

CUndefined BehaviorC89

How did I get a value larger than 8 bits in size from an 8-bit integer?

C++GccUndefined Behavior

Is passing a C++ object into its own constructor legal?

C++ClassConstructorLanguage LawyerUndefined Behavior

Does "Undefined Behavior" really permit *anything* to happen?

C++CLanguage LawyerUndefined Behavior

Is using malloc for int undefined behavior until C++20

C++MallocUndefined BehaviorC++20

Detecting signed overflow in C/C++

C++CUndefined BehaviorSignedInteger Overflow

(Why) is using an uninitialized variable undefined behavior?

CUndefined BehaviorInitialization

Printing null pointers with %p is undefined behavior?

CLanguage LawyerC99Undefined BehaviorC11

Why does the first element outside of a defined array default to zero?

C++ArraysInitializationUndefined BehaviorZero Initialization

Can branches with undefined behavior be assumed unreachable and optimized as dead code?

C++Language LawyerUndefined BehaviorDead CodeUnreachable Code

Why does printf("%f",0); give undefined behavior?

C++CPrintfImplicit ConversionUndefined Behavior

Is signed integer overflow still undefined behavior in C++?

C++C++11Undefined BehaviorInteger Overflow

At what point in the loop does integer overflow become undefined behavior?

C++CUndefined BehaviorInteger Overflow

Undefined behavior and sequence points reloaded

C++Undefined BehaviorC++ FaqSequence Points

Is it legal for source code containing undefined behavior to crash the compiler?

C++Language LawyerUndefined Behavior

Program behaving strangely on online IDEs

C++Undefined BehaviorInteger Overflow

Why doesn't 'd /= d' throw a division by zero exception when d == 0?

C++Compiler OptimizationUndefined BehaviorDivisionDivide by-Zero

Is a^a or a-a undefined behaviour if a is not initialized?

CUndefined Behavior

Is masking before unsigned left shift in C/C++ too paranoid?

C++CLanguage LawyerUndefined BehaviorInteger Arithmetic

why does long long 2147483647 + 1 = -2147483648?

C++CUndefined BehaviorInteger OverflowTwos Complement

C++ compilation bug?

C++GccUndefined Behavior

What are the common undefined/unspecified behavior for C that you run into?

CLanguage LawyerUndefined BehaviorUnspecified Behavior

Is copying 2D arrays with "memcpy" technically undefined behaviour?

C++CMultidimensional ArrayLanguage LawyerUndefined Behavior

Multithreading program stuck in optimized mode but runs normally in -O0

C++MultithreadingThread SafetyUndefined BehaviorData Race

A C++ implementation that detects undefined behavior?

C++Undefined Behavior

In C++, does initializing a global variable with itself have undefined behaviour?

C++Language LawyerUndefined Behavior

Has C++ standard changed with respect to the use of indeterminate values and undefined behavior in C++14?

C++C++11Language LawyerUndefined BehaviorC++14

Why can't the C compiler optimize changing the value of a const pointer assuming that two pointers to the same variable would be illegal/UB?

CRustUndefined BehaviorStrict Aliasing

Is accessing a global array outside its bound undefined behavior?

CUndefined Behavior

Why is this an undefined behavior?

C++CUndefined Behavior

Signed overflow in C++ and undefined behaviour (UB)

C++Undefined Behavior

Is ++x %= 10 well-defined in C++?

C++Language LawyerUndefined BehaviorEvaluation

Does initialization entail lvalue-to-rvalue conversion? Is `int x = x;` UB?

C++InitializationUndefined BehaviorLanguage Lawyer

Why is a = (a+b) - (b=a) a bad choice for swapping two integers?

C++CSwapUndefined BehaviorSequence Points

Why would code explicitly call a static method via a null pointer?

C++PointersStatic MembersUndefined BehaviorDereference

Does a[a[0]] = 1 produce undefined behavior?

CLanguage LawyerC99Undefined Behavior

The behaviour of floating point division by zero

C++Floating PointLanguage LawyerUndefined BehaviorDivide by-Zero

In C99, is f()+g() undefined or merely unspecified?

CC99Undefined BehaviorSequence PointsUnspecified Behavior

When is it valid to access a pointer to a "dead" object?

CPointersLanguage LawyerUndefined Behavior

Is std::memcpy between different trivially copyable types undefined behavior?

C++Language LawyerC++17Undefined BehaviorStrict Aliasing

Code with undefined behavior in C#

C#C++Undefined Behavior

Why do constant expressions have an exclusion for undefined behavior?

C++C++11Undefined BehaviorSfinaeConstexpr

Do std::min(0.0, 1.0) and std::max(0.0, 1.0) yield undefined behavior?

C++Floating PointLanguage LawyerUndefined BehaviorC++ Standard-Library

Is undefined behavior only an issue if you are deploying on several platforms?

C++Undefined Behavior

Why does left shift operation invoke Undefined Behaviour when the left side operand has negative value?

C++CLanguage LawyerUndefined BehaviorBit Shift

Operation on ... may be undefined?

CUndefined Behavior

Does sscanf("123456789123456789123456789", "%d", &n) have defined behavior?

CScanfUndefined Behavior