Standard data types on UNIX, Linux, and Windows

Learn about standard data types on 32-bit UNIX and Linux®, 64-bit UNIX and Linux, and 64-bit Windows applications.

32-bit UNIX and Linux applications

This section is included for comparison and is based on Solaris. Any differences with other UNIX platforms are noted:

Name	Length
char	1 byte
short	2 bytes
int	4 bytes
long	4 bytes
float	4 bytes
double	8 bytes
long double	16 bytes Note that on AIX® and Linux PPC a long double is 8 bytes.
pointer	4 bytes
ptrdiff_t	4 bytes
size_t	4 bytes
time_t	4 bytes
clock_t	4 bytes
wchar_t	4 bytes Note that on AIX a wchar_t is 2 bytes.

64-bit UNIX and Linux applications

This section is based on Solaris. Any differences with other UNIX platforms are noted:

Name	Length
char	1 byte
short	2 bytes
int	4 bytes
long	8 bytes
float	4 bytes
double	8 bytes
long double	16 bytes Note that on AIX and Linux PPC a long double is 8 bytes.
pointer	8 bytes
ptrdiff_t	8 bytes
size_t	8 bytes
time_t	8 bytes
clock_t	8 bytes Note that on the other UNIX platform a clock_t is 4 bytes.
wchar_t	4 bytes Note that on AIX a wchar_t is 2 bytes.

Windows 64-bit applications

Name	Length
char	1 byte
short	2 bytes
int	4 bytes
long	4 bytes
float	4 bytes
double	8 bytes
long double	8 bytes
pointer	8 bytes Note that all pointers are 8 bytes.
ptrdiff_t	8 bytes
size_t	8 bytes
time_t	8 bytes
clock_t	4 bytes
wchar_t	2 bytes
WORD	2 bytes
DWORD	4 bytes
HANDLE	8 bytes
HFILE	4 bytes

Coding considerations on Windows

HANDLE hf;

Use

hf = CreateFile((LPCTSTR) FileName,
                Access,
                ShareMode,
                xihSecAttsNTRestrict,
                Create,
                AttrAndFlags,
                NULL);

Do not use

HFILE hf;
hf = (HFILE) CreateFile((LPCTSTR) FileName,
                        Access,
                        ShareMode,
                        xihSecAttsNTRestrict,
                        Create,
                        AttrAndFlags,
                        NULL);

as this produces an error.

size_t len fgets

Use

size_t len
while (fgets(string1, (int) len, fp) != NULL)
len = strlen(buffer);

Do not use

int len;

while (fgets(string1, len, fp) != NULL)
len = strlen(buffer);

printf

Use

printf("My struc pointer: %p", pMyStruc);

Do not use

printf("My struc pointer: %x", pMyStruc);

If you need hexadecimal output, you have to print the upper and lower 4 bytes separately.

char *ptr

Use

char * ptr1;
char * ptr2;
size_t bufLen;

bufLen = ptr2 - ptr1;

Do not use

char *ptr1;
char *ptr2;
UINT32 bufLen;

bufLen = ptr2 - ptr1;

alignBytes

Use

alignBytes = (unsigned short) ((size_t) address % 16);

Do not use

void *address;
unsigned short alignBytes;

alignBytes = (unsigned short) ((UINT32) address % 16);

len

Use

len = (UINT32) ((char *) address2 - (char *) address1);

Do not use

void *address1;
void *address2;
UINT32 len;

len = (UINT32) ((char *) address2 - (char *) address1);

sscanf

Use

MQLONG SBCSprt;

sscanf(line, "%d", &SBCSprt);

Do not use

MQLONG SBCSprt;

sscanf(line, "%1d", &SBCSprt);

%ld tries to put an 8-byte type into a 4-byte type; only use %l if you are dealing with an actual long data type. MQLONG, UINT32 and INT32 are defined to be four bytes, the same as an int on all IBM® MQ platforms: