The write() API is used to write bytes to a stream file.
The reason that I say "bytes" as opposed to saying "letters" or "words" is that a byte containing any value can be written. We are not limited to just alphanumeric strings of text. We can write the contents of a packed decimal variable, for example, or an entire data structure.
All you have to tell write() is an area of memory (and again, it doesn't care what's in that area) and length. It copies the bytes from memory to disk.
Here's what the C language prototype of write() looks like, as printed in the UNIX-type APIs manual:
Now that's a sexy looking API!
It's a "user-defined" type. It's similar in some ways to the "like" keyword in RPG. The idea is that on different platforms, the way that a byte size is stored may be different. To write code that's reusable, they have a header member called "sys/types.h" which describes the actual data types of things like "size_t", and then when you change to a different platform and use different header files, the program compiles and works on that platform as well.
On the AS/400, size_t is defined to be a 32-bit unsigned integer. In other words, it's the same as the RPG "10U 0" data type.
Now that we've covered that, here's the RPG version of the prototype. You'll want to add this to the IFSIO_H header member:
D write PR 10I 0 extproc('write') D fildes 10I 0 value D buf * value D nbyte 10U 0 value
See? Not so bad. Just a couple of integers and a pointer. no sweat.
Here's a code snippet showing a program that calls the write() API:
c eval wrdata = 'THE QUICK BROWN FOX JUMP' c if write(fd: %addr(wrdata): %size(wrdata)) c < %size(wrdata) c goto c endif