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);

}