It’s difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center. Closed 8 years ago. Locked. This question and its answers are locked … Read more
I have recently started to learn C and I am taking a class with C as the subject. I’m currently playing around with loops and I’m running into some odd behaviour which I don’t know how to explain. #include <stdio.h> int main() { int array[10],i; for (i = 0; i <=10 ; i++) { array[i]=0; … Read more
Unsigned integer overflow is well defined by both the C and C++ standards. For example, the C99 standard (§6.2.5/9) states A computation involving unsigned operands can never overflow, because a result that cannot be represented by the resulting unsigned integer type is reduced modulo the number that is one greater than the largest value that … Read more
I was reading about order of evaluation violations, and they give an example that puzzles me. 1) If a side effect on a scalar object is un-sequenced relative to another side effect on the same scalar object, the behavior is undefined. // snip f(i = -1, i = -1); // undefined behavior In this context, … Read more
I know the uninitialized local variable is undefined behaviour(UB), and also the value may have trap representations which may affect further operation, but sometimes I want to use the random number only for visual representation and will not further use them in other part of program, for example, set something with random color in a … Read more
I know that an “undefined behaviour” in C++ can pretty much allow the compiler to do anything it wants. However, I had a crash that surprised me, as I assumed that the code was safe enough. In this case, the real problem happened only on a specific platform using a specific compiler, and only if … Read more
What is undefined behavior (UB) in C and C++? What about unspecified behavior and implementation-defined behavior? What is the difference between them? 9 s 9 Undefined behavior is one of those aspects of the C and C++ language that can be surprising to programmers coming from other languages (other languages try to hide it better). … Read more
#include <stdio.h> int main(void) { int i = 0; i = i++ + ++i; printf(“%d\n”, i); // 3 i = 1; i = (i++); printf(“%d\n”, i); // 2 Should be 1, no ? volatile int u = 0; u = u++ + ++u; printf(“%d\n”, u); // 1 u = 1; u = (u++); printf(“%d\n”, u); … Read more
When asking about common undefined behavior in C, people sometimes refer to the strict aliasing rule. What are they talking about? 1Best Answer 11 A typical situation where you encounter strict aliasing problems is when overlaying a struct (like a device/network msg) onto a buffer of the word size of your system (like a pointer … Read more
What are “sequence points”? What is the relation between undefined behaviour and sequence points? I often use funny and convoluted expressions like a[++i] = i;, to make myself feel better. Why should I stop using them? If you’ve read this, be sure to visit the follow-up question Undefined behavior and sequence points reloaded. (Note: This … Read more
