Consider the following code on a platform where the ABI does not insert padding into unions: union { int xi; } x; x.xi = 1; I believe that the second line exhibits undefined behaviour as it viol...

I've tried to read up on the other questions here on SO with similar titles, but they are all a tiny bit too complex for me to be able to apply the solution (or even explanation) to my own issue, w...

Assuming I have a union like this union buffer { struct { T* data; int count; int capacity; }; struct { void* data; int count; int capacity; } __type_erased; }; Will I get into trouble if I mi...

Questions: Does this code below violate strict aliasing rules? That is, would a smart compiler be allowed to print 00000 (or some other nasty effect), because a buffer first accessed as other typ...

Does the following program violate the strict aliasing rule? #include <cstdint> int main() { double d = 0.1; //std::int64_t n = *reinterpret_cast<std::int64_t*>(&d); // aliasin...

See http://pubs.opengroup.org/onlinepubs/009696699/basedefs/sys/socket.h.html (http://pubs.opengroup.org/onlinepubs/9699919799 is from Issue 7 - from 2013 and still the same!) sockaddr_stor...

I'm confused by the strict aliasing rules when it comes to casting a char array to other types. I know that it is permitted to cast any object to a char array, but I'm not sure what happens the oth...

Just a couple weeks ago, I learned that the C++ Standard had a strict aliasing rule. Basically, I had asked a question about shifting bits -- rather than shifting each byte one at a time, to maximi...

I recently was surprised to learn that the C and C++ language standards have a "strict aliasing" rule. In essence, the rule prohibits variables of differing types from referencing the same memory l...

I recently learned that the C++ standard contains "strict aliasing rules", which forbid referencing the same memory location via variables of different types. However, the standard does allows for...

I used the following piece of code to read data from files as part of a larger program. double data_read(FILE *stream,int code) { char data[8]; switch(code) { case 0x08: return (unsigned char)...

Suppose we have a pointer T* ptr; and ptr, ptr+1, … ptr+(n-1) all refer to valid objects of type T. Is it possible to access them as if they were an STL array? Or does the following code: std::ar...

I am trying to determine whether the following code invokes undefined behavior: #include <iostream> class A; void f(A& f) { char* x = reinterpret_cast<char*>(&f); for (int i...

One of the first results for strict aliasing on google is this article http://dbp-consulting.com/tutorials/StrictAliasing.html One interesting thing I noticed is this: http://goo.gl/lPtIa5 uint32_...

The Question The question of whether all pointers derived from pointers to structure types are the same, is not easy to answer. I find it to be a significant question for the following two primary...

Consider the following code (p is of type unsigned char* and bitmap->width is of some integer type, exactly which is unknown and depends on which version of some external library we're using): ...

Suppose we get some data as a sequence of bytes, and want to reinterpret that sequence as a structure (having some guarantees that the data is indeed in the correct format). For example: #include ...

Me and a colleague are trying to achieve a simple polymorphic class hierarchy. We're working on an embedded system and are restricted to only using a C compiler. We have a basic design idea that co...

I have looked at the following — related — questions, and none of them seem to address my exact issue: one, two, three. I am writing a collection of which the elements (key-value pairs) are stored...

I have a Result<T> template class that holds a union of some error_type and T. I would like to expose the common part (the error) in a base class without resorting to virtual functions. Here...

According to both C99 §6.2.5p27 and C11 §6.2.5p28: All pointers to structure types shall have the same representation and alignment requirements to each other. With a footnote (#39 and #48 re...

I'm proposing a change to a library whose public API currently looks like this: typedef size_t enh; /* handle */ int en_open(enh *handle) { struct internal *e = malloc(...); *handle = (enh)e; ...

I've got a question about strict-aliasing rules, unions and standard. Assume we have the following code: #include <stdio.h> union { int f1; short f2; } u = {0x1}; int * a = &u.f1; sh...

I am facing confusion about the C++ strict-aliasing rule and its possible implications. Consider the following code: int main() { int32_t a = 5; float* f = (float*)(&a); *f = 1.0f; int32_...

I've been trying to understand a particular aspect of strict aliasing recently, and I think I have made the smallest possible interesting piece of code. (Interesting for me, that is!) Update: Base...