It’s actually quite common to store a number without needing to know the exact size of the type. There are plenty of quantities in my programs that I can reasonably assume won’t exceed 2 billion, or enforce that they don’t. But that doesn’t mean I need an exact 32 bit type to store them, any … Read more
size_t is defined by the C standard to be the unsigned integer return type of the sizeof operator (C99 6.3.5.4.4), and the argument of malloc and friends (C99 7.20.3.3 etc). The actual range is set such that the maximum (SIZE_MAX) is at least 65535 (C99 7.18.3.2). However, this doesn’t let us determine sizeof(size_t). The implementation … Read more
The following could be ambiguous: sizeof int * + 1 Is that (sizeof (int*)) + 1, or (sizeof(int)) * (+1)? Obviously the C language could have introduced a rule to resolve the ambiguity, but I can imagine why it didn’t bother. With the language as it stands, a type specifier never appears “naked” in an … Read more
“…after all it’s just a pointer…”? No. Array is not a pointer. Array is an array object: a solid continuous block of memory that stores the array elements, no pointers of any kind involved. In your case array has 6 elements of size 4 each. That is why your sizeof evaluates to 24. The common … Read more
The question is not meaningful, at least not without further context. The notion of “size” in Java is only reasonably well defined for primitives: A byte is 8 bit (unsurprisingly) an int is 32 bit, a long 64bit, etc. (see e.g. http://download.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html for a full list). For object instances, it’s more complicated, because: Object instances … Read more
C++ arrays are fixed in size. If you need a “resizable array”, you’ll want to use std::vector instead of an array.
What you are trying to do is not possible to do in any elegant way. It is not possible to reliably access consecutive struct members as an array. The currently accepted answer is a hack, not a solution. The proper solution would be to switch to an array, regardless of how much work it is … Read more
It’s padding the struct to fit an 8-byte boundary. So it actually is taking 40 bytes in memory – sizeof is returning the correct value. If you want it to only take 33 bytes then specify the packed attribute: struct region { public: long long int x; long long int y; long long int width; … Read more
Yes, your assumption is correct, assuming an int and a pointer are both 4 bytes long on your machine. And no, arrays aren’t pointers. The array name sometimes decays into a pointer in certain contexts, but they aren’t the same thing. There is a whole section of the comp.lang.c FAQ dedicated to this common point … Read more
The result of pointer subtraction is in elements and not in bytes. Thus the first expression evaluates to 1 by definition. This aside, you really ought to use parentheses in macros: #define my_sizeof(x) ((&x + 1) – &x) #define my_sizeof(x) ((char *)(&x + 1) – (char *)&x) Otherwise attempting to use my_sizeof() in an expression … Read more