Solaris系统编程 基本的文件IO

 from：《Solaris系统编程》Rich Teer : 93.

处理网络设备，终端和streams设备上的IO程序：

#include <unistd.h>

#include <errno.h>

 

ssize_t readn (int fd, void *buf, size_t num)

{

         ssize_t res;

         size_t n;

         char *ptr;

 

         n = num;

         ptr = buf;

         while (n > 0) {

                   if ((res = read (fd, ptr, n)) == -1) {

                            if (errno == EINTR)

                                     res = 0;

                            else

                                     return (-1);

                   }

                   else if (res == 0)

                            break;

 

                   ptr += res;

                   n -= res;

         }

 

         return (num - n);

}

 

ssize_t writen (int fd, const void *buf, size_t num)

{

         ssize_t res;

         size_t n;

         const char *ptr;

 

         n = num;

         ptr = buf;

         while (n > 0) {

                   if ((res = write (fd, ptr, n)) <= 0) {

                            if (errno == EINTR)

                                     res = 0;

                            else

                                     return (-1);

                   }

 

                   ptr += res;

                   n -= res;

         }

 

         return (num);

}