Menu
I've seen both (size_t)-1 and ~0 used to represent large numbers, or numbers with all their bits flipped.
Is there any difference between the two? If so, what is it?
I found this question: What is the difference between -1 and ~0, however it did not answer my question because I'm dealing with unsigned integers (such as size_t), as opposed to signed integers (such as int).
688
The size_t data type is never negative.
The type's size is chosen so that it could store the maximum size of a theoretically possible array of any type. On a 32-bit system size_t will take 32 bits, on a 64- bit one 64 bits. In other words, a variable of size_t type can safely store a pointer.
size_t is the unsigned integer type of the result of sizeof , _Alignof (since C11) and offsetof, depending on the data model. The bit width of size_t is not less than 16.
It is okay to compare a size_t value with an int value, the int value will be implicitly converted to unsigned type. Some compilers will issue a warning when you mix signed and unsigned types in comparisons.
In C++, int is considered the basic signed integer type. It’s understood that int will be at least 16 bits wide. On the other hand, size_t is considered an unsigned integer featuring enough bytes to accommodate any size type.
The size_t data type is never negative. Therefore many C library functions like malloc, memcpy and strlen declare their arguments and return type as size_t. For instance, size_t or any unsigned type might be seen used as loop variable as loop variables are typically greater than or equal to 0.
No, size 4 is not the same as 5T. It is a size smaller than 5T. 5T will be longer and broader than size 4 and can accommodate a diaper. The bottom of size 4 will not be big enough to accommodate a diaper. Thus, only a fully potty trained toddler can use size 4. If your child is not potty trained or has a bigger build, you should opt for 5T.
An array is also declared with the size x. size_t is a datatype of unsigned integral variable x. It is calculating the size of variable a in bytes. printf ("SIZE_MAX = %lu ", SIZE_MAX); size_t size = sizeof (a);
What's the difference between (size_t)-1 and ~0?
Type and value differ.
(size_t)-1 is the same value as SIZE_MAX and has a type of size_t.
~0 is often -1 and has the type of int.
Assigning both of those to a size_t will result in SIZE_MAX.
size_t a = (size_t)-1;
size_t b = ~0;
In the 2nd case, -1 is assigned to a b and undergoes a conversion first, wrapping around the -1 to the maximum size_t value.
161
(size_t)-1 is of type size_t. It typically has a value of 232-1 or 264-1 (4294967295 or 18446744073709551615).
~0 is of type int, and has the value -1 on a 2's-complement system (i.e., just about everywhere).
Both are likely to have the same bit pattern -- if int and size_t are the same size, which they very commonly are not.
If you want the maximum value of type size_t, you can use the SIZE_MAX macro, defined in <stdint.h>. If you're using an older implementation (pre-C99) that doesn't provide SIZE_MAX, (size_t)-1 will work. I'm not sure why you'd want to write ~0 rather than -1 -- unless perhaps you're considering non-two's-complement systems.
21
Note that the previous answers assume a 2's complement machine (very likely to be the case these days, but not guaranteed).
If you had a sign-magnitude machine then -1 would have a sign bit and least significant bit set with all others clear, if you had a 1's complement machine then -1 would have all bits but the LSB set.
In all of these cases (including the common 2's complement machine), ~0 has all bits set.
39
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
