C Implementation Differences

C Implementation Differences

This section lists differences between the 32-bit and the 64-bit C implementations. Because both compilers adhere to the ANSI standard, and because C is a rigorously defined language designed to be portable, there are not many differences between the 32-bit and 64-bit compiler implementations. The only areas where differences can occur are in data types (by definition) and in areas where ANSI does not define the precise behavior of the language.

Table 2-3 summarizes the differences in data types under the 32-bit and 64-bit data type models.

Differences in Data Type Sizes
C type 32-bit 64-bit
char 8 8
short int 16 16
int 32 32
long int 32 64
long long int 64 64
pointer 32 64
float 32 32
double 64 64
long double[1] 64 128

Differences in Data Type Sizes
C type	32-bit	64-bit
char	8	8
short int	16	16
int	32	32
long int	32	64
long long int	64	64
pointer	32	64
float	32	32
double	64	64
long double[1]	64	128

Table 2-3 shows that long ints, pointers and long doubles are different under the two models.

[1] On 32-bit compiles the long double data type generates a warning message indicating that the long qualifier is not supported.

Structure and Union Layout Examples
Portability Issues