Show error message upon error opening log file

[xrobin]

The CifCheck command fails silently when it cannot write to the *-diag.log file (eg if $PWD is read-only). ofstream::open() is unchecked and validation errors are lost. With no output and an exit code of 0, it looks exactly like the input file passed validation.

Steps to reproduce

#  Create the test directory and a minimally invalid CIF file:
mkdir -p /tmp/test_mmcif
cat > /tmp/test_mmcif/invalid.cif << 'EOF'
data_test
_invalid_category.field value
EOF

# Remove write permission on the directory:
rm invalid.cif-diag.log
chmod a-w /tmp/test_mmcif

# Run CifCheck
CifCheck -f invalid.cif -dictSdb /path/to/mmcif_pdbx_v50.sdb

Observation

Command runs successfully, no error display, exit code 0, no diagnostic file invalid.cif-diag.log

Expected output

This should have displayed an error and, preferably, exited with a non 0 exit code.

Proposed solution

I opened a pull request in rcsb/cpp-cif-file#1 with a proposed fix.