Clang static code analyser: The left operand of '!=' is a garbage value

[DimitriPapadopoulos]

The Clang static code analyser emits a warning:

$ scan-build clang -c ini.c 
scan-build: Using '/usr/lib/llvm-18/bin/clang' for static analysis
ini.c:164:56: warning: The left operand of '!=' is a garbage value [core.UndefinedBinaryOperatorResult]
  164 |         if (offset == max_line - 1 && line[offset - 1] != '\n') {
      |                                       ~~~~~~~~~~~~~~~~ ^
1 warning generated.
scan-build: Analysis run complete.
scan-build: 1 bug found.
scan-build: Run 'scan-view /tmp/scan-build-2026-01-05-114423-34279-1' to examine bug reports.
$ 

While it looks like a false positive, it would be nice to silence the warning message. One way to do that would be to initialise line in ini_reader_string:

#ifdef __clang_analyzer__
    memset(str, '\0', num);
#endif

See also openconnect/ocserv#437.

[benhoyt]

I do think this is a false positive. I'm not sure about silencing it with that workaround: I think the game of chasing the various linters/analysers with such workarounds is a never-ending battle, and your code starts to get littered with more and more things like this. So I'd prefer not to add this. Could you disable that warning in your build system? Is the Clang analyser being too strict?

[DimitriPapadopoulos]

Indeed, if offset is the length of line:

        offset = strlen(line);

I don't see how line[offset - 1] could be garbage:

        if (offset == max_line - 1 && line[offset - 1] != '\n') {

Why doesn't the Clang analyser complain about strlen(line) in the first place, if it thinks the contents of line are garbage?

We need to convince the Clang analyser that ini_reader_string does not terminate line/str with '\0' without setting prior characters. My hope is that it could be easily done, while clarifying the source code and thus improving maintainability.

Unfortunately, I haven't find an easy and elegant way to silence the anaylser yet.