long long是8个字节，什么意思？

Question

I've read the answers to the question of why sizeof(long long) is 8 on most systems, but I'm still not sure how to interpret the meaning of them.

One of the reasons given is that there is a lot of code 'out there' which assumes that sizeof(long long) <= sizeof(size_t) . That makes sense. Then there are all kinds of views on architecture conventions and brands, etc. I don't even want to get into those debates about the history of the convention. There are also reasons given that long long can be any size according to standard, but I think that is not really what concerns me.

What I want to know is how to interpret the difference now between the fact that sizeof(long long) returns 8 but that a long long actually is 16. Should it be interpreted as a historical remnant that applies only to the sizeof operator, or is there an underlying address pointer associated with that fact, so that operations on a long long are executed in 8 byte increments?

Sizeof (signed) long v4: 8 Value of (x at 2147483647)v4: 7fffffff

Sizeof long long v5: 8 Value of (x at 9223372036854775807)v5: 7fffffffffffffff

Answer 1

According to the standard, long long is at least 64 bits, or say, 8 bytes.

On most machines today, it is 8 bytes long. sizeof (BTW, an operator, not a function) returns its size, you can count on it. There's no way sizeof(long long) is 8 while the size of long long is 16 .

Answer 2

The longest standard data type is 8 bytes (64 bits) on most of the systems, Which is long long .

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In addition you can include limits.h which library contains defined values for each data type and the space it occupies on your system.

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A slight update during the fact I've encountered some level of interest over long . It is guaranteed to be at least 32 bits (or 4 bytes) long. So as long int (though in that case, long is rather a length modifier).

Answer 3

问题是您的系统的一部分已切换到 64 位，而您的系统的一部分仍在以 32 位运行。

Answer 4

Somewhere there is a confusion and I am not sure where it is, because you don't say where you get your numbers from, so I will try to clarify the basics.

sizeof returns by definition the number of bytes a type occupies. On all modern systems a byte is composed of 8 bits, but on some esoteric or old architectures a byte has other number of bits. CHAR_BIT from limits.h tells you how many bits there are in a byte. But again, on all modern architectures that's 8.

sizeof(long long) returns 8 but that a long long actually is 16.

That is not true. If sizoef(long long) is 8 then long long is 8 bytes long.

The follow-up question would be why sizeof(long) returns 8, but only holds 4bytes.

Again, not true. If sizeof (long) is 8 then long holds 8 bytes.

The question turns out to be whether we ought to anticipate the elimination of the 4byte long, or not.

Not a chance in hell. One of the pillars of C and C++ is backwards compatibility. Removing a fundamental type would break practically every program on the planet.

If you ask if there is any use of the type long when int and long long seem to cover everything then again the answer is int and long long don't cover everything. There are system like eg arduino where sizeof int == 2 , sizeof long == 4 and sizeof long long == 8 .