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

cli/cmdlineparser.cpp

@@ -1837,9 +1837,13 @@ 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>             Ignore files that match <str>. <str> can be a filename\n"
+        "                         or directory and can contain *,**,?. A file that is\n"
+        "                         ignored will not be checked directly (the whole\n"
+        "                         translation unit is skipped completely). Header files\n"
+        "                         are checked indirectly when they are #include'd.\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
+### Ignore 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 ignored.
 
-    cppcheck -isrc/c src
+A file that is ignored will not be checked directly (the complete translation unit is skipped). Any header #include'd from a source file which is not ignored is checked indirectly, regardless if the header is ignored.
 
-The `-i` option is not used during preprocessing, it can't be used to exclude headers that are included.
+> *Note*: If you want to filter out warnings for a header file then `-i` will not work. Use suppressions instead.
 
 You can use `**`, `*` and `?` in the pattern to specify excluded folders/files.  
 `**`: matches zero or more characters, including path separators