Question

I read the man pages, and my understanding is that if write() fails and sets the errno to EAGAIN or EINTR, I may perform the write() again, so I came up with the following code:

  ret = 0;
  while(ret != count) {
    write_count = write(connFD, (char *)buf + ret,  count);
    while (write_count < 0) {
      switch(errno) {
        case EINTR:
        case EAGAIN:
          write_count = write(connFD, (char *)buf + ret,  count -ret);
          break;
        default:
          printf("\n The value of ret is : %d\n", ret);
          printf("\n The error number is : %d\n", errno);      
          ASSERT(0);
      }
    }
    ret += write_count;
  }

I am performing read() and write() on sockets and handling the read() similarly as above. I am using Linux, with gcc compiler.

Answer 1

You have a bit of a “don’t repeat yourself” problem there – there’s no need for two separate calls to write, nor for two nested loops.

My normal loop would look something like this:

for (int n = 0; n < count; ) {
    int ret = write(fd, (char *)buf + n, count - n);
    if (ret < 0) {
         if (errno == EINTR || errno == EAGAIN) continue; // try again
         perror("write");
         break;
    } else {
        n += ret;
    }
}

// if (n < count) here some error occurred