UNIX编程(2)-UNIX标准化

1.ISO c
2.IEEE POSIX
3.Single UNIX Specification (XSI)
4.查看系统限制的函数

#include <unistd.h>

long sysconf(int name);

long pathconf(const char *pathname, int name);

long fpathconf(int filedes, int name);


例：打印所有可能的sysconf和pathconf的值

#include "apue.h"
#include <errno.h>
#include <limits.h>

static void pr_sysconf(char *, int);
static void pr_pathconf(char *, char *, int);

int
main(int argc, char *argv[])
{
    if (argc != 2)
        err_quit("usage: a.out <dirname>");

#ifdef ARG_MAX
    printf("ARG_MAX defined to be %d\n", ARG_MAX+0);
#else
    printf("no symbol for ARG_MAX\n");
#endif
#ifdef _SC_ARG_MAX
    pr_sysconf("ARG_MAX =", _SC_ARG_MAX);
#else
    printf("no symbol for _SC_ARG_MAX\n");
#endif

/* similar processing for all the rest of the sysconf symbols... */

#ifdef MAX_CANON
    printf("MAX_CANON defined to be %d\n", MAX_CANON+0);
#else
    printf("no symbol for MAX_CANON\n");
#endif
#ifdef _PC_MAX_CANON
    pr_pathconf("MAX_CANON =", argv[1], _PC_MAX_CANON);
#else
    printf("no symbol for _PC_MAX_CANON\n");
#endif

/* similar processing for all the rest of the pathconf symbols... */

   exit(0);
}
static void
pr_sysconf(char *mesg, int name)
{
    long    val;

    fputs(mesg, stdout);
    errno = 0;
    if ((val = sysconf(name)) < 0) {
        if (errno != 0) {
            if (errno == EINVAL)
                fputs(" (not supported)\n", stdout);
            else
                err_sys("sysconf error");
        } else {
            fputs(" (no limit)\n", stdout);
        }
    } else {
        printf(" %ld\n", val);
    }
}

static void
pr_pathconf(char *mesg, char *path, int name)
{
    long    val;

    fputs(mesg, stdout);
    errno = 0;
    if ((val = pathconf(path, name)) < 0) {
        if (errno != 0) {
            if (errno == EINVAL)
                fputs(" (not supported)\n", stdout);
            else
                err_sys("pathconf error, path = %s", path);
        } else {
            fputs(" (no limit)\n", stdout);
        }
    } else {
        printf(" %ld\n", val);
    }
}

5.基本系统数据类型


caddr_t
core address 
clock_t
counter of clock ticks (process time) 
comp_t
compressed clock ticks 
dev_t
device numbers (major and minor) 
fd_set
file descriptor sets 
fpos_t
file position 
gid_t
numeric group IDs

ino_t
i-node numbers 
mode_t
file type, file creation mode
nlink_t
link counts for directory entries 
off_t
file sizes and offsets (signed)
pid_t
process IDs and process group IDs (signed)
ptrdiff_t
result of subtracting two pointers (signed)

rlim_t
resource limits
sig_atomic_t
data type that can be accessed atomically
sigset_t
signal set
size_t
sizes of objects (such as strings) (unsigned)
ssize_t
functions that return a count of bytes (signed) (read, write)

time_t
counter of seconds of calendar time 
uid_t
numeric user IDs

wchar_t
can represent all distinct character codes