alx‭

What does it mean that we can use memcmp(3) on invalid values? ISO C allows comparing an invalid value through memcmp(3), because it doesn't read the value, but rather its representation, and "rea...

2 answers  ·  posted 2y ago by alx‭  ·  last activity 2y ago by Lundin‭

Is it valid to partly allocate an object, as long as you only use the allocated part of it? #include <stdio.h> #include <stdlib.h> struct s { int i[100]; }; int main(void) {...

1 answer  ·  posted 2y ago by alx‭  ·  last activity 2y ago by Lundin‭

It's a long story. Once upon a time, there were three ways to express a null pointer constant: NULL 0 ((char *) 0) This was true at least as far back as Unix V7 (1979). Maybe even further...

posted 2mo ago by alx‭  ·  edited 26d ago by alx‭

How can we use git-send-email(1) to sign patches (emails) with the gpg(1) keyring? I've heard it can be done, but couldn't find anything in the git-send-email(1) documentation nor in a web search.

3 answers  ·  posted 2y ago by alx‭  ·  last activity 8mo ago by alx‭

Let's consider the following code: const char a[][4] = {"aa", "aaa"}; const char *b[] = {"bb", "bbb"}; const char *const c[] = {"cc", "ccc"}; For shared libraries, both b and c arrays require...

0 answers  ·  posted 2y ago by alx‭  ·  edited 2y ago by alx‭

Is it legal ISO C to declare a function as noreturn with a non-void return type (but of course not actually returning)? As far as I can read from the standard, it seems legal. Example: noreturn ...

1 answer  ·  posted 3y ago by alx‭  ·  edited 3y ago by alx‭

char *p, *q; p = malloc(1); free(p); q = p; // lvalue conversion Is the last lvalue conversion (= p;) Undefined Behavior or not? We didn't take the address of the local p. C11::6.3.2.1...

2 answers  ·  posted 1y ago by alx‭  ·  last activity 1y ago by Dirk Herrmann‭

Let's say we have an object, we store it in a union (into some other narrower type, but with memcpy(3), so it's allowed --I guess--), and then read it from the union via it's original type (so no a...

2 answers  ·  posted 1y ago by alx‭  ·  last activity 1y ago by Lundin‭

I've seen macros use parentheses to enclose its arguments. Most of these make sense, as in #define sum(a, b) ((a) + (b)) The outer prevents the following: #define sum_bad(a, b) (a) + (b) ...

2 answers  ·  posted 1y ago by alx‭  ·  last activity 1y ago by Lundin‭

Is -isystem/path/to/sys/includes a standard compiler option, or is it a compiler extension implemented by gcc, clang, and maybe other compilers? Can I rely on its availability? I couldn't find th...

1 answer  ·  posted 2y ago by alx‭  ·  last activity 2y ago by deleted user

How to write a macro that discards the const qualifier, for any type? I hope some combination of typeof and a cast will do, but haven't found the combination. I tried this, without luck: #define...

2 answers  ·  posted 2y ago by alx‭  ·  last activity 2y ago by alx‭

I'd like to assert that some code can be optimized out, and is not present in the final binary object. #define CONSTANT 0 #if (!CONSTANT) [[landmine_A]] #endif static int foo(void); void...

1 answer  ·  posted 2y ago by alx‭  ·  last activity 2y ago by alx‭

Let's analyze this code, assuming an architecture where the alignment of int64_t is the same as that of double: void bar(double *f, int64_t *j) { *(int64_t *)f = *j; } void foo(void) ...

1 answer  ·  posted 2y ago by alx‭  ·  edited 2y ago by Lundin‭

strcpy(3) can be safe. Some compilers, such as GCC and Clang, use a feature test macro, _FORTIFY_SOURCE, (see feature_test_macros(7) https://man7.org/linux/man-pages/man7/feature_test_macros.7.htm...

posted 1y ago by alx‭

I was directed a few days ago to a post about a string copy function, which IMO improves the commonly known string copy functions, including strlcpy(3BSD), strlcat(3BSD), and strscpy(9). It define...

2 answers  ·  posted 3y ago by alx‭  ·  last activity 2y ago by alx‭