Checking for NULL field in C when using Record I/O - part 2

Hello,

thanks to Javier Mora for reminding me about this topic. :-)

Thanks to Mark's answer from last October, I found some more breadcrumbs to follow.

https://archive.midrange.com/c400-l/202410/msg00001.html

The PDF mentioned by Mark says:

When you read from a database file, the corresponding byte in the null field map is indicated with a character '1' if the field is considered null. This is specified in the null field map pointed to by the in_null_map pointer.


I changed my CGI program to decide upon said character:

if (docs_data_nullfld.SUBTITLE == '0') {
do things if field is not NULL …

Unfortunately, this never matches, and hence the "field is not NULL" code is never branched to.


Debugging. When I do a

printf("0x%0X\n", docs_data_nullfld.SUBTITLE);

Im getting a 0x1 when the field is NULL, and 0x2 when it's not. Neither in ASCII nor in EBCDIC, numerals are encoded in character positions 0x1 or 0x2.

This leaves me greatly confused.


When I do a

if (docs_data_nullfld.SUBTITLE != '1') {
do things if field is not NULL …

branches to the correct code. Duh! So I basically got it to work.


I understand that the documentation mentions just the NULL case associated with an '1', but not that a field not being NULL is actually '0'. My bad.

If someone can shed some light upon the seemingly bogus values being output by my "hex" printf, I'm most interested!

Thanks!

:wq! PoC