C++ application terminates with 143 exit code - what does it mean?

There are some exit codes which have either defined or generally agreed upon meaning.

In case of 143, which is 128 + 15, that means program died with signal 15, which is SIGTERM

According to the above table, exit codes 1 - 2, 126 - 165, and 255 have special meanings, and should therefore be avoided for user-specified exit parameters.

See the table at http://www.tldp.org/LDP/abs/html/exitcodes.html

143 usually means the application caught a SIGTERM signal, meaning the process was killed. This could be because another process killed it, or perhaps because the operating system killed it for using too much memory or some other resource, etc. Without more information, it's hard to know.