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

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 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

Name Length
char 1 byte
short 2 bytes
int 4 bytes
long 8 bytes
float 4 bytes
double 8 bytes
long double 8 bytes
pointer 8 bytes
ptrdiff_t 8 bytes
size_t 8 bytes
time_t 8 bytes
clock_t 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);
    For 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 we 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:

Parent topic: Coding standards on 64-bit platforms