C++ – What does the C++ standard state the size of int, long type to be


I'm looking for detailed information regarding the size of basic C++ types.
I know that it depends on the architecture (16 bits, 32 bits, 64 bits) and the compiler.

But are there any standards for C++?

I'm using Visual Studio 2008 on a 32-bit architecture. Here is what I get:

char  : 1 byte
short : 2 bytes
int   : 4 bytes
long  : 4 bytes
float : 4 bytes
double: 8 bytes

I tried to find, without much success, reliable information stating the sizes of char, short, int, long, double, float (and other types I didn't think of) under different architectures and compilers.

Best Answer

The C++ standard does not specify the size of integral types in bytes, but it specifies minimum ranges they must be able to hold. You can infer minimum size in bits from the required range. You can infer minimum size in bytes from that and the value of the CHAR_BIT macro that defines the number of bits in a byte. In all but the most obscure platforms it's 8, and it can't be less than 8.

One additional constraint for char is that its size is always 1 byte, or CHAR_BIT bits (hence the name). This is stated explicitly in the standard.

The C standard is a normative reference for the C++ standard, so even though it doesn't state these requirements explicitly, C++ requires the minimum ranges required by the C standard (page 22), which are the same as those from Data Type Ranges on MSDN:

  1. signed char: -127 to 127 (note, not -128 to 127; this accommodates 1's-complement and sign-and-magnitude platforms)
  2. unsigned char: 0 to 255
  3. "plain" char: same range as signed char or unsigned char, implementation-defined
  4. signed short: -32767 to 32767
  5. unsigned short: 0 to 65535
  6. signed int: -32767 to 32767
  7. unsigned int: 0 to 65535
  8. signed long: -2147483647 to 2147483647
  9. unsigned long: 0 to 4294967295
  10. signed long long: -9223372036854775807 to 9223372036854775807
  11. unsigned long long: 0 to 18446744073709551615

A C++ (or C) implementation can define the size of a type in bytes sizeof(type) to any value, as long as

  1. the expression sizeof(type) * CHAR_BIT evaluates to a number of bits high enough to contain required ranges, and
  2. the ordering of type is still valid (e.g. sizeof(int) <= sizeof(long)).

Putting this all together, we are guaranteed that:

  • char, signed char, and unsigned char are at least 8 bits
  • signed short, unsigned short, signed int, and unsigned int are at least 16 bits
  • signed long and unsigned long are at least 32 bits
  • signed long long and unsigned long long are at least 64 bits

No guarantee is made about the size of float or double except that double provides at least as much precision as float.

The actual implementation-specific ranges can be found in <limits.h> header in C, or <climits> in C++ (or even better, templated std::numeric_limits in <limits> header).

For example, this is how you will find maximum range for int:


#include <limits.h>
const int min_int = INT_MIN;
const int max_int = INT_MAX;


#include <limits>
const int min_int = std::numeric_limits<int>::min();
const int max_int = std::numeric_limits<int>::max();