Is int in C Always 32

 

This is related to following question,

How to Declare a 32-bit Integer in C

Several people mentioned int is always 32-bit on most platforms. I am curious if this is true.

Do you know any modern platforms with int of a different size? Ignore dinosaur platforms with 8-bit or 16-bit architectures.

NOTE: I already know how to declare a 32-bit integer from the other question. This one is more like a survey to find out which platforms (CPU/OS/Compiler) supporting integers with other sizes.

As several people have stated, there are no guarantees that an 'int' will be 32 bits, if you want to use variables of a specific size, particularly when writing code that involves bit manipulations, you should use the 'Standard Integer Types' mandated by the c99 specification. 

int8_t
uint8_t
int32_t
uint32_t

etc...

they are generally of the form [u]intN_t, where the 'u' specifies that you want an unsigned quantity, and N is the number of bits

the correct typedefs for these should be available in stdint.h on whichever platform you are compiling for, using these allows you to write nice, portable code :-)

"is always 32-bit on most platforms" - what's wrong with that snippet? :-)

The C standard does not mandate the sizes of its variables. It does mandate relative sizes, for example, sizeof(int) >= sizeof(short) and so on. It also mandates minimum ranges but allows for multiple encoding schemes (two's complement, ones' complement, and sign/magnitude).

If you want a specific sized variable, you need to use one suitable for the platform you're running on, such as the use of #ifdef 's, something like: 

#ifdef LONG_IS_32BITS
    typedef long int32;
#else
    #ifdef INT_IS_32BITS
        typedef int int32;
    #else
        #error No 32-bit data type available
    #endif
#endif

Alternatively, C99 allows for exact width integer types intN_t and uintN_t :

  • The typedef name intN_t designates a signed integer type with width N , no padding bits, and a two's complement representation. Thus, int8_t denotes a signed integer type with a width of exactly 8 bits.
  • The typedef name uintN_t designates an unsigned integer type with width N . Thus, uint24_t denotes an unsigned integer type with a width of exactly 24 bits.
  • These types are optional. However, if an implementation provides integer types with widths of 8, 16, 32, or 64 bits, no padding bits, and (for the signed types) that have a two's complement representation, it shall define the corresponding typedef names.

    • At this moment in time, most desktop and server platforms use 32-bit integers, and even many embedded platforms (think handheld ARM or x86) use 32-bit int s. To get to a 16-bit int you have to get very small indeed: think "Berkeley mote" or some of the smaller Atmel Atmega chips. But they are out there.

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