Is an int a 64-bit integer in 64-bit C#?_问答_开发者

In my C# source code I may have declared integers as:

int i = 5;

Int32 i = 5;

In the currently prevalent 32-bit world they are equivalent. However, as we move into a 64-bit world, am I correct in saying that the following will become the same?

int i开发者_运维技巧 = 5;
Int64 i = 5;

No. The C# specification rigidly defines that int is an alias for System.Int32 with exactly 32 bits. Changing this would be a major breaking change.

The int keyword in C# is defined as an alias for the System.Int32 type and this is (judging by the name) meant to be a 32-bit integer. To the specification:

CLI specification section 8.2.2 (Built-in value and reference types) has a table with the following:

System.Int32 - Signed 32-bit integer

C# specification section 8.2.1 (Predefined types) has a similar table:

int - 32-bit signed integral type

This guarantees that both System.Int32 in CLR and int in C# will always be 32-bit.

Will sizeof(testInt) ever be 8?

No, sizeof(testInt) is an error. testInt is a local variable. The sizeof operator requires a type as its argument. This will never be 8 because it will always be an error.

VS2010 compiles a c# managed integer as 4 bytes, even on a 64 bit machine.

Correct. I note that section 18.5.8 of the C# specification defines sizeof(int) as being the compile-time constant 4. That is, when you say sizeof(int) the compiler simply replaces that with 4; it is just as if you'd said "4" in the source code.

Does anyone know if/when the time will come that a standard "int" in C# will be 64 bits?

Never. Section 4.1.4 of the C# specification states that "int" is a synonym for "System.Int32".

If what you want is a "pointer-sized integer" then use IntPtr. An IntPtr changes its size on different architectures.

int is always synonymous with Int32 on all platforms.

It's very unlikely that Microsoft will change that in the future, as it would break lots of existing code that assumes int is 32-bits.

I think what you may be confused by is that int is an alias for Int32 so it will always be 4 bytes, but IntPtr is suppose to match the word size of the CPU architecture so it will be 4 bytes on a 32-bit system and 8 bytes on a 64-bit system.

According to the C# specification ECMA-334, section "11.1.4 Simple Types", the reserved word int will be aliased to System.Int32. Since this is in the specification it is very unlikely to change.

No matter whether you're using the 32-bit version or 64-bit version of the CLR, in C# an int will always mean System.Int32 and long will always mean System.Int64.

The following will always be true in C#:

sbyte signed 8 bits, 1 byte

byte unsigned 8 bits, 1 byte

short signed 16 bits, 2 bytes

ushort unsigned 16 bits, 2 bytes

int signed 32 bits, 4 bytes

uint unsigned 32 bits, 4 bytes

long signed 64 bits, 8 bytes

ulong unsigned 64 bits, 8 bytes

An integer literal is just a sequence of digits (eg 314159) without any of these explicit types. C# assigns it the first type in the sequence (int, uint, long, ulong) in which it fits. This seems to have been slightly muddled in at least one of the responses above.

Weirdly the unary minus operator (minus sign) showing up before a string of digits does not reduce the choice to (int, long). The literal is always positive; the minus sign really is an operator. So presumably -314159 is exactly the same thing as -((int)314159). Except apparently there's a special case to get -2147483648 straight into an int; otherwise it'd be -((uint)2147483648). Which I presume does something unpleasant.

Somehow it seems safe to predict that C# (and friends) will never bother with "squishy name" types for >=128 bit integers. We'll get nice support for arbitrarily large integers and super-precise support for UInt128, UInt256, etc. as soon as processors support doing math that wide, and hardly ever use any of it. 64-bit address spaces are really big. If they're ever too small it'll be for some esoteric reason like ASLR or a more efficient MapReduce or something.

Yes, as Jon said, and unlike the 'C/C++ world', Java and C# aren't dependent on the system they're running on. They have strictly defined lengths for byte/short/int/long and single/double precision floats, equal on every system.

int without suffix can be either 32bit or 64bit, it depends on the value it represents.

as defined in MSDN: