# How to delete redundant false alarm markers

As the analyzer evolves or the analyzed code changes, a warning on false positive may stop appearing, and false alarm markers left in the source code for that warning become redundant\.

When such redundant markers accumulate, they clutter the code and can cause a new warning to go unnoticed when it appears in the same spot\.

To clean the codebase of redundant false alarm markers, PVS\-Studio distribution includes a dedicated utility: `pvs-fp-cleaner`\.

## False alarm markers for deletion

To suppress [false\-positive warnings](https://pvs-studio.com/en/docs/manual/0017/), PVS\-Studio analyzer supports control comments of the following type:

**//\-V**_warning\-number_

The `warning-number` is the_ _[diagnostic rule](https://pvs-studio.com/en/docs/warnings/) number_\._

Examples of false alarm markers:

```cpp
if (a == b && a == b && 0 / 0 == 0) //-V501 //-V609
```

If you suppress a false positive using the [hash code mechanism](https://pvs-studio.com/en/docs/manual/6630/#enable_false_alarms_with_hash), the tool also considers the following markers for removal:

**//\-VH"**_hash_**"**

The `hash` is the hash code of a line excluding comments\.

Here is an example of a marker with a hash code:

```cpp
if (a == b && a == b && 0 / 0 == 0) //-V501 //-V609 //-VH"12345678"
```

## How to collect information about redundant markers

The first step in removing redundant false alarm markers is to thoroughly analyze the project in a special mode\.


> Currently, you can collect information only using the \`pvs\-studio\-analyzer\` / \`CompilerCommandsAnalyzer\` utilities\\\.



The `pvs-studio-analyzer` / `CompilerCommandsAnalyzer` utility:

```cpp
pvs-studio-analyzer analyze --redundant-false-alarms=/path/to/report.json \
                            --sourcetree-root=/path/to/project-root \
                            ....
```

As a result, a report on redundant false alarm markers will be created\.

Required flags:

* `redundant-false-alarms` is the path to the created report on redundant false alarm markers;
* `sourcetree-root` is the flag to specify the root directory \(`/path/to/project`\) of the project for building [relative paths](https://pvs-studio.com/en/docs/manual/0027/)\.

## How to automatically delete redundant markers

To automatically delete redundant false alarm markers from the codebase, the distribution includes the `pvs-fp-cleaner` utility\.


> When you analyze code on different platforms, the analyzer may issue different warnings\\\. So, for cross\\\-platform projects, generate a separate report for each platform and pass all of these reports as input parameters to the cleanup utility\\\.



After analyzing the project and receiving the report, you can run the cleanup utility by specifying the following arguments:

```cpp
pvs-fp-cleaner cleanup \
               --sourcetree-root=/path/to/project \
               PATH...
```

where

* `cleanup` is the utility mode;
* `PATH...` is a list of paths to reports on redundant false alarm markers;
* `sourcetree-root` is the path to the project root directory for converting relative paths from reports on different platforms\.

The example:

```cpp
pvs-fp-cleaner cleanup \
               --sourcetree-root=/home/user/project \
               /home/user/windows_report.json \
               /home/user/linux_report.json \
               /home/user/macOS_report.json
```


> We recommend running the utility in the automatic cleanup mode on a codebase managed by a version control system such as Git, SVN, or Mercurial\\\. If the project does not use version control, make sure to create a backup of the source files beforehand\\\.



## How to merge reports on redundant false alarm markers

If you need to merge several reports on redundant markers, for example, for a cross\-platform project, you can also use the `pvs-fp-cleaner` utility\.

```cpp
pvs-fp-cleaner merge \
               --sourcetree-root=/path/to/project \
               --output-file=/path/to/merged_report.json \
               PATH...
```

where

* `merge` is the utility mode\.
* `sourcetree-root` is the path to the project root directory for converting relative paths from reports on different platforms\. It is also used to merge information in identical files when analyzing them from different platforms\.
* `output-file` is the path to the resulting report after merging\.
* `PATH...` is a list of paths to reports on redundant false alarm markers\.

The example:

```cpp
pvs-fp-cleaner merge \
               --sourcetree-root=/home/user/project \
               --output-file=/home/user/merged_report.json \
               /home/user/windows_report.json \
               /home/user/linux_report.json \
               /home/user/macOS_report.json
```

## How to create a report for preview

Before deleting false alarm markers, it may be useful to assess the scale of changes in the codebase\. You can use the utility to create a report for previewing the detected redundant markers\.

You can use the `report` mode to generate such a report:

```cpp
pvs-fp-cleaner report \
               --sourcetree-root=/home/user/project \
               --output-file=/home/user/report_for_IDE_plugin.json \
               PATH...
```

where

* `report` is the utility mode\.
* `sourcetree-root` is the path to the project root directory for converting relative paths from reports on different platforms\. In the `report` mode, it is mandatory only when generating a report from "raw" core reports\.
* `output-file` is the path to the resulting report\.
* `PATH...` is a list of paths to reports on redundant false alarm markers\.

You can open the created report in your IDE using the provided plugins:

![pvs-fp-cleaner/image1.png](https://import.viva64.com/docx/blog/pvs-fp-cleaner/image1.png)