The one line description: I found the difference between #include <a.h> and #include “a.h”.

I had problems finding compiling some sample C code which included

#include <__iew_api.h>

I was getting

WARNING CCN3296  #include file <__iew_api.h> not found.

There were a couple of problem. The length of the name __iew_api is more than 8 characters, so will not be in a PDS or PDSE. I found it in /usr/include.

In my JCL for comping C programs I had

LSEARCH(/usr/include/)

But still it was not found. After a cup of tea and walk down to the shops I wondered if it was the include that was causing the problems.

I changed it to

#include "__iew_api.h" 

and it found it. The documentation says

The file_path can be an absolute or relative path. If the double quotation marks are used, … the preprocessor adds the directory of the including file to the list of paths to be searched for the included file.
If the double angle brackets are used, … the preprocessor does not add the directory of the including file to the list of paths to be searched for the included file.