#include <stdio.h> #include <sys/types.h> int main() { printf(“pid_t: %zu\n”, sizeof(pid_t)); printf(“uid_t: %zu\n”, sizeof(uid_t)); printf(“gid_t: %zu\n”, sizeof(gid_t)); } EDIT: Per popular request (and because, realistically, 99% of the people coming to this question are going to be running x86 or x86_64)… On an i686 and x86_64 (so, 32-bit and 64-bit) processor running Linux >= 3.0.0, the … Read more
TL;DR – sizeof works on the type of the operand. sizeof(ch) == sizeof (char)——————-(1) sizeof(‘a’) == sizeof(int) ——————–(2) sizeof (‘a’+ ‘b’ + ‘c’) == sizeof(int) —(3) sizeof (“a”) == sizeof (char [2]) ———-(4) Let’s see each case now. ch is defined to be of char type, so , pretty straightforward. In C, sizeof(‘a’) is the … Read more
sizeof and strlen() do different things. In this case, your declaration char string[] = “october”; is the same as char string[8] = “october”; so the compiler can tell that the size of string is 8. It does this at compilation time. However, strlen() counts the number of characters in the string at run time. So, … Read more
In C ‘a’ is an integer constant (!?!), so 4 is correct for your architecture. It is implicitly converted to char for the assignment. sizeof(char) is always 1 by definition. The standard doesn’t say what units 1 is, but it is often bytes.
The keyword int aliases System.Int32 which still requires 4 bytes, even on a 64-bit machine.
A union always takes up as much space as the largest member. It doesn’t matter what is currently in use. union { short x; int y; long long z; } An instance of the above union will always take at least a long long for storage. Side note: As noted by Stefano, the actual space … Read more
From 5.3.2 [expr.sizeof] When applied to a class, the result [of sizeof] is the number of bytes in an object of that class including any padding required for placing objects of that type in an array. The size of a most derived class shall be greater than zero (1.8). From 1.8 [intro.object] Unless it is … Read more
The standard says that SIZE_MAX must be at least 65535. It specifies no upper bound, and gcc’s implementation is perfectly valid. Quoting the reference you cited (emphasis added): Its implementation-defined value shall be equal to or greater in magnitude (absolute value) than the corresponding value given below, with the same sign.
It’s necessary to satisfy an invariant from the C++ standard: every C++ object of the same type needs to have a unique address to be identifiable. If objects took up no space, then items in an array would share the same address.
void() is a function type (it’s a function which takes no arguments and returns nothing), so it’s not a valid type in sizeof().