readn, writen和readline函数

#include <unistd.h>
#include <errno.h>

ssize_t readn(int fd, void *buf, size_t count)
{
  char *strtmp;
  ssize_t reval, realcount=0;
  strtmp = (char *)buf;
  
  while (count>0)
  {
    reval = read(fd, strtmp, count);
    if (reval<0)
      if (errno == EINTR)
        continue;
      else return -1;
    else if (reval>0)
    {
      count -= reval;
      strtmp += reval;
      realcount += reval;
      continue;
    }
    else break;
  }
  
  return realcount;
}

ssize_t writen(int fd, const void *buf, size_t count)
{
  char *strtmp;
  ssize_t reval, realcount=count;
  strtmp = (char *)buf;
  
  while(count>0)
  {
    reval = write(fd, strtmp, count);
    if (reval < 0)
      if (errno == EINTR)
        continue;
      else return -1;
      
    count -= reval;
    strtmp += reval;
  }
  
  return realcount;
}
ssize_t readline(int fd, void *buf, int size)
{
  char *strtmp;
  ssize_t reval, realcount=0;
  strtmp = (char *)buf;
 
  while(size>1)
  {
    reval = read(fd, strtmp, 1);
    if (reval<0)
      if (errno == EINTR)
        continue;
      else return -1;
    else if (reval == 0)
      break;
    else
    {
      realcount++;
      size--;
      if (*strtmp++ =='\n')
        break;
    }
  }
  *strtmp='\0';
  return realcount;
}