C/C++: Size of builtin types for various compilers/platforms

Question

Where can I go to get information about the size of, say, unsigned int compiling under gcc for Mac OS X (both 32 and 64 bits)? In general I'd love to have a resource I can go to with a compiler/settings/platform/type and be able to look up how big that type will be. Does anyone know of such a thing?

Update: Thanks for all the responses. I was hoping to have something more along the lines of a static table somewhere instead of a piece of code I'd have to write and run on every machine.

Answer 1

You could write a test program that uses sizeof calls on all the types you're interested in. Might also be useful to check limits.h.

Answer 2

You may query the length of a data type with the sizeof operator. For example:

#include <stdio.h> 
#include <inttypes.h> 

#define PRINT_SIZEOF(type)  printf("sizeof( " #type " ) == %zi\n", sizeof(type) )

int main(void){
  PRINT_SIZEOF( short        );
  PRINT_SIZEOF( unsigned int );
  PRINT_SIZEOF( long         );
  PRINT_SIZEOF( long long    );
  PRINT_SIZEOF( uint64_t     );
}

EDIT: %i changed to %zi

Answer 3

you could probably write some simple shell script that prompts for a type and when you enter it it compiles something like what sambowry posted and executes it to tell you what the size of it is..

Answer 4

Generic method of sambowry's method (C++):

#include <iostream>
#include <typeinfo>

template <typename T>
void print_sizeof(void)
{
    std::cout << "sizeof(" <<
        typeid(T).name() << ") == " <<
        sizeof(T) << std::endl;
}

int main(void)
{
    print_sizeof<short>();
    print_sizeof<unsigned int>();
    print_sizeof<long>();
    print_sizeof<long long>();
    print_sizeof<uint64_t>();
}

Note the compiler isn't required to give you an actual string for name, but most do.

Answer 5

If you can't write a program to find out, you should consult the ABI (Application Binary Interface) specification for the compiler/platform. It should document the sizes, alignments, endianness, etc. of the basic primitive types supported.

Answer 6

In general, you don't need to know exact sizes if you include stdint.h. There are defined several very useful types.

If you want exact size, use these:

int8_t
uint8_t
int16_t
uint16_t
int32_t
uint32_t
int64_t
uint64_t

If you want at least the specified size, use these:

int_least8_t
uint_least8_t
int_least16_t
uint_least16_t
int_least32_t
uint_least32_t
int_least64_t
uint_least64_t

If you want at least the specified size optimized for speed, use these:

int_fast8_t
uint_fast8_t
int_fast16_t
uint_fast16_t
int_fast32_t
uint_fast32_t
int_fast64_t
uint_fast64_t