What is undefined behavior in C?

In computer programming, undefined behavior (UB) is the result of executing a program whose behavior is prescribed to be unpredictable, in the language specification to which the computer code adheres. … In the C community, undefined behavior may be humorously referred to as “nasal demons”, after a comp. std.

What is undefined programming?

In computing (particularly, in programming), undefined value is a condition where an expression does not have a correct value, although it is syntactically correct. … In other type systems an undefined value can mean an unknown, unpredictable value, or merely a program failure on attempt of its evaluation.

Is unsigned overflow undefined behavior?

In languages like C, unsigned integer overflow reliably wraps around; e.g., UINT_MAX + 1 yields zero. … In contrast, the C standard says that signed integer overflow leads to undefined behavior where a program can do anything, including dumping core or overrunning a buffer. The misbehavior can even precede the overflow.

Does rust have undefined behavior?

Rust should not have much undefined behavior, however it may have surprising behavior.

Why is it difficult to detect and debug vulnerabilities in code that are based on undefined behavior?

Undefined behaviors may also cause security vulnerabilities, especially due the cases when array out of bound is not checked (causes buffer overflow attack). C and C++ have undefined behaviors because it allows compilers to avoid lots of checks.

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How do you know if a value is undefined?

In a JavaScript program, the correct way to check if an object property is undefined is to use the typeof operator. If the value is not defined, typeof returns the ‘undefined’ string.26 мая 2018 г.

How do you find undefined values?

A rational expression is undefined when the denominator is equal to zero. To find the values that make a rational expression undefined, set the denominator equal to zero and solve the resulting equation. Example: 0 7 2 3 x x − Is undefined because the zero is in the denominator.

How is overflow detected?

Overflow occurs with respect to the size of the data type that must accommodate the result. Overflow indicates that the result was too large or too small to fit in the original data type. When two signed 2’s complement numbers are added, overflow is detected if: both operands are positive and the result is negative, or.

Why is signed overflow undefined?

— the sign bit has the value −(2N − 1) (one’s complement). Nowadays, all processors use two’s complement representation, but signed arithmetic overflow remains undefined and compiler makers want it to remain undefined because they use this undefinedness to help with optimization.

How do you deal with overflow?


  1. Be aware of overflow!
  2. Know the range of inputs to arithmetic operations in your program.
  3. Use compiler flags to ensure wraparound semantics ( -fwrapv in clang and gcc)
  4. Use explicit saturation where appropriate.
  5. Beware of the pathological cases involving INT_MIN.

What is 1ull?

1ULL is ‘unsigned long long’. This is probably intended to be an unsigned, 64-bit number.

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What does uninitialized mean in C++?

object has not been

What does implementation mean?

11.1 Implementation-defined behavior. … This term means that the implementation is free to do what it likes, but must document its choice and stick to it. The mapping of physical source file multi-byte characters to the execution character set.

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