Fixed #14266 (documentation: clarify how -i works)

cli/cmdlineparser.cpp

@@ -1837,9 +1837,10 @@ void CmdLineParser::printHelp(bool premium) const
         "                         this is not needed.\n"
         "    --include=<file>\n"
         "                         Force inclusion of a file before the checked file.\n"
-        "    -i <str>             Exclude source files or directories matching str from\n"
-        "                         the check. This applies only to source files so header\n"
-        "                         files included by source files are not matched.\n"
+        "    -i <str>             Skip translation units whose *source filename* matches\n"
+        "                         '<str>'. '<str>' can be a filename or directory.\n"
+        "                         Note: If you want to prevent warnings in some headers,\n"
+        "                         use suppressions instead.\n"
         "    --inconclusive       Allow that Cppcheck reports even though the analysis is\n"
         "                         inconclusive.\n"
         "                         There are false positives with this option. Each result\n"

man/manual.md

@@ -126,13 +126,13 @@ Typically a `compile_commands.json` contains absolute paths. However no matter i
  * a file with relative path `src/test2.c` can be checked.
  * a file with relative path `src/test3.cpp` is not checked.
 
-### Excluding a file or folder from checking
+### Exclude files matching a given pattern
 
-The option `-i` specifies a pattern to files/folders to exclude. With this command no files in `src/c` are checked:
+With `-i <str>` you can configure filename/directory patterns that should be excluded from checking.
 
-    cppcheck -isrc/c src
+> *Note*: If you want to filter out warnings for a header file then `-i` will not work. The option `--suppress` should be used instead.
 
-The `-i` option is not used during preprocessing, it can't be used to exclude headers that are included.
+Translation units are skipped if their *source filename* matches the exclusion pattern. This filtering happens *before* preprocessing, and the exclusion patterns are not applied during preprocessing or analysis.
 
 You can use `**`, `*` and `?` in the pattern to specify excluded folders/files.  
 `**`: matches zero or more characters, including path separators