# Cppcheck 1.83

2018-01-21

## Introduction

Cppcheck is an analysis tool for C/C++ code. Unlike C/C++ compilers and many other analysis tools, it doesn't detect syntax errors. Instead, Cppcheck detects the types of bugs that the compilers normally fail to detect. The goal is no false positives.

Supported code and platforms:

- You can check non-standard code that includes various compiler extensions, inline assembly code, etc.

- Cppcheck should be compilable by any C++ compiler that handles the latest C++ standard.

- Cppcheck should work on any platform that has sufficient CPU and memory.

Please understand that there are limits of Cppcheck. Cppcheck is rarely wrong about reported errors. But there are many bugs that it doesn't detect.

You will find more bugs in your software by testing your software carefully, than by using Cppcheck. You will find more bugs in your software by instrumenting your software, than by using Cppcheck. But Cppcheck can still detect some of the bugs that you miss when testing and instrumenting your software.

## Getting started (GUI)

Start the GUI.

### New Project

It is not required but creating a new project file is a good first step. You do so through `File` and `New project file.`

### New Project - Paths and Defines

What kind of project do you have? If it is a Visual Studio project or if you can generate a compile database (cmake/qbs/etc), then you can import the project.

Otherwise you can configure the paths and defines manually. In this screenshot below, a Visual Studio project file is imported:

### New Project - Project

In the Project tab it is highly recommended that a `Cppcheck build dir` is configured. This will be used by Cppcheck to store various analysis information. It gives you whole program analysis, incremental analysis, statistics, etc. Each project should have its own unique build dir. In the screenshot below the build dir is configured as `cppcheck-build-dir`. The path is relative to the project file.

You should also choose all the libraries that you use. In the screenshot below the microsoft_sal and windows libraries are selected. You can read more about libraries in this manual.

### New Project - Addons

We skip the `Exclude` and `Suppressions` tabs now, they can be used later to tweak the results.

In the Addons tab you can add extra analysis. The addons require python.

### Analyze

Click the `OK` button in the dialog. Analysis will start immediately.

All warnings are activated and therefore it is pretty noisy. There are likely various warnings that you don't care about. You can fix that easily, right click on messages and choose `Hide` or `Suppress`. Hiding messages is not permanent, they will be shown after next analysis. Suppressing messages is permanent, suppressed ids are stored in the project file and those will not be shown again.

## Getting started (command line)

### First test

Here is a simple code

    int main()
    {
        char a[10];
        a[10] = 0;
        return 0;
    }

If you save that into `file1.c` and execute:

    cppcheck file1.c

The output from cppcheck will then be:

    Checking file1.c...
    [file1.c:4]: (error) Array 'a[10]' index 10 out of bounds

### Checking all files in a folder

Normally a program has many source files. And you want to check them all. Cppcheck can check all source files in a directory:

    cppcheck path

If "path" is a folder then cppcheck will recursively check all source files in this folder.

    Checking path/file1.cpp...
    1/2 files checked 50% done
    Checking path/file2.cpp...
    2/2 files checked 100% done

### Check files manually or use project file

With Cppcheck you can check files manually, by specifying files/paths to check and settings. Or you can use a project file (cmake/visual studio).

Using the project file is quicker since it requires very little configuration from you.

Checking files manually gives you better control of the analysis.

We don't know which approach will give you the best results. It is recommended that you try both. It is possible that you will get different results so that to find most bugs you need to use both approaches.

Later chapters will describe this in more detail.

### Excluding a file or folder from checking

To exclude a file or folder, there are two options. The first option is to only provide the paths and files you want to check.

    cppcheck src/a src/b

All files under `src/a` and `src/b` are then checked.

The second option is to use -i, with it you specify files/paths to ignore. With this command no files in `src/c` are checked:

    cppcheck -isrc/c src

This option does not currently work with the --project option and is only valid when supplying an input directory.To ignore multiple directories supply the -i multiple times. The following command ignores both the src/b and src/c directories.

    cppcheck -isrc/b -isrc/c

### Severities

The possible severities for messages are:

error

  used when bugs are found

warning

  suggestions about defensive programming to prevent bugs

style

  stylistic issues related to code cleanup (unused functions, redundant code, constness, and such)

performance

  Suggestions for making the code faster. These suggestions are only based on common knowledge. It is not certain you'll get any measurable difference in speed by fixing these messages.

portability

  portability warnings. 64-bit portability. code might work different on different compilers. etc.

information

  Configuration problems. The recommendation is to only enable these during configuration.

### Enable messages

By default only error messages are shown. Through the --enable command more checks can be enabled.

    # enable warning messages
    cppcheck --enable=warning file.c

    # enable performance messages
    cppcheck --enable=performance file.c

    # enable information messages
    cppcheck --enable=information file.c

    # For historical reasons, --enable=style enables warning, performance,
    # portability and style messages. These are all reported as "style" when
    # using the old xml format.
    cppcheck --enable=style file.c

    # enable warning and performance messages
    cppcheck --enable=warning,performance file.c

    # enable unusedFunction checking. This is not enabled by --enable=style
    # because it doesn't work well on libraries.
    cppcheck --enable=unusedFunction file.c

    # enable all messages
    cppcheck --enable=all

Please note that `--enable=unusedFunction` should only be used when the whole program is scanned. Therefore, `--enable=all` should also only be used when the whole program is scanned. The reason is that the unusedFunction checking will warn if a function is not called. There will be noise if function calls are not seen.

#### Inconclusive checks

By default Cppcheck only writes error messages if it is certain. With --inconclusive error messages will also be written when the analysis is inconclusive.

    cppcheck --inconclusive path

This can of course cause false warnings, it might be reported that there are bugs even though there are not. Only use this command if false warnings are acceptable.

### Saving results in file

Many times you will want to save the results in a file. You can use the normal shell redirection for piping error output to a file.

    cppcheck file1.c 2> err.txt

### Multithreaded checking

The option `-j` is used to specify the number of threads you want to use. For example, to use 4 threads to check the files in a folder:

    cppcheck -j 4 path

Please note that this will disable unusedFunction checking.

### Platform

You should use a platform configuration that match your target.

By default Cppcheck uses native platform configuration that works well if your code is compiled and executed locally.

Cppcheck has builtin configurations for `unix` and `windows` targets. You can easily use these with the `--platform` command line flag.

You can also create your own custom platform configuration in a xml file. Here is an example:

    <?xml version="1"?>
    <platform>
      <char_bit>8</char_bit>
      <default-sign>signed</default-sign>
      <sizeof>
        <short>2</short>
        <int>4</int>
        <long>4</long>
        <long-long>8</long-long>
        <float>4</float>
        <double>8</double>
        <long-double>12</long-double>
        <pointer>4</pointer>
        <size_t>4</size_t>
        <wchar_t>2</wchar_t>
      </sizeof>
    </platform>

## Project

When you use CMake or Visual Studio you can use `--project` to analyse your project.

It will give you quick and easy results. There is not much configuration you need to do. But it is hard to say if this will give you the best results, it is recommended that you try it and also try to analyse your source code without `--project` and see which option works best for you.

### CMake

Cppcheck can understand compile databases. You can generate these with CMake.

Example:

    $ cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=ON .

The file `compile_commands.json` is created in the current folder.

Now run Cppcheck like this:

    $ cppcheck --project=compile_commands.json

### Visual Studio

You can run Cppcheck on individual project files (*.vcxproj) or on a whole solution (*.sln)

    # run cppcheck on a whole solution
    $ cppcheck --project=foobar.sln

    # run cppcheck on a individual project
    $ cppcheck --project=foobar.vcxproj

Please note that there is also a Visual Studio plugin that allows you to run cppcheck inside Visual Studio.

## Preprocessor settings

If you use `--project` then Cppcheck will use the preprocessor settings from the project file.

Otherwise you'll probably want to configure the include paths, defines etc.

### Defines

Here is a file that has 2 configurations (with A defined and without A):

    #ifdef A
        x = y;
    #else
        x = z;
    #endif

By default Cppcheck will check all preprocessor configurations (except those that have #error in them). So the above code will be analysed both when A is defined and when it is not.

You can use -D to change this. When you use -D, cppcheck will by default only check the given configuration and nothing else. This is how compilers work. But you can use `--force` or `--max-configs` to override the number of configurations.

    # check all configurations
    cppcheck file.c

    # only check the configuration A
    cppcheck -DA file.c

    # check all configurations when macro A is defined
    cppcheck -DA --force file.c

Another useful flag might be -U. It undefines a symbol. Example usage:

    cppcheck -UX file.c

That will mean that X is not defined. Cppcheck will not check what happens when X is defined.

### Include paths

To add an include path, use -I, followed by the path.

Cppcheck's preprocessor basically handles includes like any other preprocessor. However, while other preprocessors stop working when they encounter a missing header, cppcheck will just print an information message and continues parsing the code.

The purpose of this behaviour is that cppcheck is meant to work without necessarily seeing the entire code. Actually, it is recommended to not give all include paths. While it is useful for cppcheck to see the declaration of a class when checking the implementation of its members, passing standard library headers is highly discouraged because it will result in worse results and longer checking time. For such cases, .cfg files (see below) are the better way to provide information about the implementation of functions and types to cppcheck.

## XML output

Cppcheck can generate output in `XML` format. Use --xml to enable this format.

A sample command to check a file and output errors in the `XML` format:

    cppcheck --xml file1.cpp

Here is a sample report:

    <?xml version="1.0" encoding="UTF-8"?>
    <results version="2">
      <cppcheck version="1.66">
      <errors>
        <error id="someError" severity="error" msg="short error text"
               verbose="long error text" inconclusive="true" cwe="312">
          <location file0="file.c" file="file.h" line="1"/>
        </error>
      </errors>
    </results>

### The <error> element

Each error is reported in a `<error>` element. Attributes:

id

  id of error. These are always valid symbolnames.

severity

  either: `error`, `warning`, `style`, `performance`, `portability` or `information`

msg

  the error message in short format

verbose

  the error message in long format.

inconclusive

  This attribute is only used when the message is inconclusive.

cwe

  CWE ID for message. This attribute is only used when the CWE ID for the message is known.

### The <location> element

All locations related to an error is listed with `<location>` elements. The primary location is listed first.

Attributes:

file

  filename. Both relative and absolute paths are possible

file0

  name of the source file (optional)

line

  a number

info

  short information message for each location (optional)

## Reformatting the output

If you want to reformat the output so it looks different you can use templates.

To get Visual Studio compatible output you can use --template=vs:

    cppcheck --template=vs gui/test.cpp

This output will look like this:

    Checking gui/test.cpp...
    gui/test.cpp(31): error: Memory leak: b
    gui/test.cpp(16): error: Mismatching allocation and deallocation: k

To get gcc compatible output you can use --template=gcc:

    cppcheck --template=gcc gui/test.cpp

The output will look like this:

    Checking gui/test.cpp...
    gui/test.cpp:31: error: Memory leak: b
    gui/test.cpp:16: error: Mismatching allocation and deallocation: k

You can write your own pattern (for example a comma-separated format):

    cppcheck --template="{file},{line},{severity},{id},{message}" gui/test.cpp

The output will look like this:

    Checking gui/test.cpp...
    gui/test.cpp,31,error,memleak,Memory leak: b
    gui/test.cpp,16,error,mismatchAllocDealloc,Mismatching allocation and deallocation: k

The following format specifiers are supported:

callstack

  callstack - if available

file

  filename

id

  message id

line

  line number

message

  verbose message text

severity

  a type/rank of message

The escape sequences \b (backspace), \n (newline), \r (formfeed) and \t (horizontal tab) are supported.

## Misra

Cppcheck has an addon that checks for `MISRA` C 2012 compliance.

### Requirements

You need:

- Python 2.X or 3.X

- `The MISRA C 2012` PDF. You can buy this from http://www.misra.org.uk (costs 15-20 pounds)

### MISRA Text file

It is not allowed to publish the `MISRA` rule texts. Therefore the `MISRA` rule texts are not available directly in the addon. Instead, the addon can read the rule texts from a text file. If you copy/paste all text in "Appendix A Summary of guidelines" from the MISRA pdf, then you have all the rule texts.

If you have installed `xpdf`, such text file can be generated on the command line (using `pdftotext` that is included in `xpdf`):

    pdftotext misra-c-2012.pdf output.txt

The output might not be 100% perfect so you might need to make minor tweaks manually.

Other pdf-to-text utilities might work also.

To create the text file manually, copy paste Appendix A "Summary of guidelines" from the MISRA PDF. Format:

    Appendix A Summary of guidelines
    Rule 1.1
    Rule text
    Rule 1.2
    Rule text
    ...

Rules that you want to disable does not need to have a rule text. Rules that don't have rule text will be suppressed by the addon.

## Suppressions

If you want to filter out certain errors you can suppress these.

### Suppressing a certain error type

You can suppress certain types of errors. The format for such a suppression is one of:

    [error id]:[filename]:[line]
    [error id]:[filename2]
    [error id]

The error id is the id that you want to suppress. The easiest way to get it is to use the --xml command line flag. Copy and paste the id string from the XML output. This may be `*` to suppress all warnings (for a specified file or files).

The filename may include the wildcard characters `*` or `?`, which match any sequence of characters or any single character respectively. It is recommended that you use "/" as path separator on all operating systems.

#### Command line suppression

The --suppress= command line option is used to specify suppressions on the command line. Example:

    cppcheck --suppress=memleak:src/file1.cpp src/

#### Listing suppressions in a file

You can create a suppressions file. Example:

    // suppress memleak and exceptNew errors in the file src/file1.cpp
    memleak:src/file1.cpp
    exceptNew:src/file1.cpp

    // suppress all uninitvar errors in all files
    uninitvar

Note that you may add empty lines and comments in the suppressions file.

You can use the suppressions file like this:

    cppcheck --suppressions-list=suppressions.txt src/

### Inline suppressions

Suppressions can also be added directly in the code by adding comments that contain special keywords. Before adding such comments, consider that the code readability is sacrificed a little.

This code will normally generate an error message:

    void f() {
        char arr[5];
        arr[10] = 0;
    }

The output is:

    # cppcheck test.c
    Checking test.c...
    [test.c:3]: (error) Array 'arr[5]' index 10 out of bounds

To suppress the error message, a comment can be added:

    void f() {
        char arr[5];

        // cppcheck-suppress arrayIndexOutOfBounds
        arr[10] = 0;
    }

Now the --inline-suppr flag can be used to suppress the warning. No error is reported when invoking cppcheck this way:

    cppcheck --inline-suppr test.c

## Library configuration

When external libraries are used, such as WinAPI, POSIX, gtk, Qt, etc, `Cppcheck` doesn't know how the external functions behave. `Cppcheck` then fails to detect various problems such as leaks, buffer overflows, possible null pointer dereferences, etc. But this can be fixed with configuration files.

Cppcheck already contains configurations for several libraries. They can be loaded as described below. Note that the configuration for the standard libraries of C and C++, `std.cfg`, is always loaded by cppcheck. If you create or update a configuration file for a popular library, we would appreciate if you upload it to us.

### Using your own custom .cfg file

You can create and use your own .cfg files for your projects. Use `--check-library` and `--enable=information` to get hints about what you should configure.

It is recommended that you use the `Library Editor` in the `Cppcheck GUI` to edit configuration files. It is available in the `View` menu. All settings are not documented in this manual.

If you have a question about the `.cfg` file format it is recommended you ask in the forum (http://sourceforge.net/p/cppcheck/discussion/).

The command line cppcheck will try to load custom .cfg files from the working path - execute cppcheck from the path where the .cfg files are.

The cppcheck GUI will try to load custom .cfg files from the project file path. The custom .cfg files should be shown in the `Edit Project File` dialog that you open from the `File` menu.

### Memory/resource leaks

Cppcheck has configurable checking for leaks, e.g. you can specify which functions allocate and free memory or resources and which functions do not affect the allocation at all.

#### alloc and dealloc

Here is an example program:

    void test()
    {
        HPEN pen = CreatePen(PS_SOLID, 1, RGB(255,0,0));
    }

The code example above has a resource leak - `CreatePen()` is a WinAPI function that creates a pen. However, Cppcheck doesn't assume that return values from functions must be freed. There is no error message:

    # cppcheck pen1.c
    Checking pen1.c...

If you provide a configuration file then `Cppcheck` detects the bug:

    # cppcheck --library=windows.cfg pen1.c
    Checking pen1.c...
    [pen1.c:3]: (error) Resource leak: pen

Here is a minimal `windows.cfg` file:

    <?xml version="1.0"?>
    <def>
      <resource>
        <alloc>CreatePen</alloc>
        <dealloc>DeleteObject</dealloc>
      </resource>
    </def>

The allocation and deallocation functions are organized in groups. Each group is defined in a `<resource>` or `<memory>` tag and is identified by its `<dealloc>` functions. This means, groups with overlapping `<dealloc>` tags are merged.

#### leak-ignore and use

Often the allocated pointer is passed to functions. Example:

    void test()
    {
        char *p = malloc(100);
        dostuff(p);
    }

If Cppcheck doesn't know what `dostuff` does, without configuration it will assume that `dostuff` takes care of the memory so there is no memory leak.

To specify that `dostuff` doesn't take care of the memory in any way, use `leak-ignore` in the `<function>` tag (see next section):

    <?xml version="1.0"?>
    <def>
      <function name="dostuff">
        <leak-ignore/>
        <arg nr="1"/>
      </function>
    </def>

If instead `dostuff` takes care of the memory then this can be configured with:

    <?xml version="1.0"?>
    <def>
      <memory>
        <dealloc>free</dealloc>
        <use>dostuff</use>
      </memory>
    </def>

The `<use>` configuration has no logical purpose. You will get the same warnings without it. Use it to silence `--check-library` information messages.

### Function behaviour

To specify the behaviour of functions and how they should be used, `<function>` tags can be used. Functions are identified by their name, specified in the `name` attribute and their number of arguments. The name is a comma-separated list of function names. For functions in namespaces or classes, just provide their fully qualified name. For example: `<function name="memcpy,std::memcpy">`. If you have template functions then provide their instantiated names `<function name="dostuff<int>">`.

#### Function arguments

The arguments a function takes can be specified by `<arg>` tags. Each of them takes the number of the argument (starting from 1) in the `nr` attribute, `nr="any"` for arbitrary arguments, or `nr="variadic"` for variadic arguments. Optional arguments can be specified by providing a default value: `default="value"`. The specifications for individual arguments override this setting.

##### Not bool

Here is an example program with misplaced comparison:

    void test()
    {
        if (MemCmp(buffer1, buffer2, 1024==0)) {}
    }

`Cppcheck` assumes that it is fine to pass boolean values to functions:

    # cppcheck notbool.c
    Checking notbool.c...

If you provide a configuration file then Cppcheck detects the bug:

    # cppcheck --library=notbool.cfg notbool.c
    Checking notbool.c...
    [notbool.c:5]: (error) Invalid MemCmp() argument nr 3. A non-boolean value is required.

Here is the minimal notbool.cfg

    <?xml version="1.0"?>
    <def>
      <function name="MemCmp">
        <arg nr="1"/>
        <arg nr="2"/>
        <arg nr="3">
          <not-bool/>
        </arg>
      </function>
    </def>

##### Uninitialized memory

Here is an example program:

    void test()
    {
        char buffer1[1024];
        char buffer2[1024];
        CopyMemory(buffer1, buffer2, 1024);
    }

The bug here is that buffer2 is uninitialized. The second argument for CopyMemory needs to be initialized. However, `Cppcheck` assumes that it is fine to pass uninitialized variables to functions:

    # cppcheck uninit.c
    Checking uninit.c...

If you provide a configuration file then Cppcheck detects the bug:

    # cppcheck --library=windows.cfg uninit.c
    Checking uninit.c...
    [uninit.c:5]: (error) Uninitialized variable: buffer2

Note that this implies for pointers that the memory they point at has to be initialized, too.

Here is the minimal `windows.cfg`:

    <?xml version="1.0"?>
    <def>
      <function name="CopyMemory">
        <arg nr="1"/>
        <arg nr="2">
          <not-uninit/>
        </arg>
        <arg nr="3"/>
      </function>
    </def>

##### Null pointers

Cppcheck assumes it's ok to pass NULL pointers to functions. Here is an example program:

    void test()
    {
        CopyMemory(NULL, NULL, 1024);
    }

The MSDN documentation is not clear if that is ok or not. But let's assume it's bad. Cppcheck assumes that it's ok to pass NULL to functions so no error is reported:

    # cppcheck null.c
    Checking null.c...

If you provide a configuration file then `Cppcheck` detects the bug:

    cppcheck --library=windows.cfg null.c
    Checking null.c...
    [null.c:3]: (error) Null pointer dereference

Note that this implies `<not-uninit>` as far as values are concerned. Uninitialized memory might still be passed to the function.

Here is a minimal `windows.cfg` file:

    <?xml version="1.0"?>
    <def>
      <function name="CopyMemory">
        <arg nr="1">
          <not-null/>
        </arg>
        <arg nr="2"/>
        <arg nr="3"/>
      </function>
    </def>

##### Format string

You can define that a function takes a format string. Example:

    void test()
    {
        do_something("%i %i\n", 1024);
    }

No error is reported for that:

    # cppcheck formatstring.c
        Checking formatstring.c...

A configuration file can be created that says that the string is a format string. For instance:

    <?xml version="1.0"?>
    <def>
      <function name="do_something">
        <formatstr type="printf"/>
        <arg nr="1">
          <formatstr/>
        </arg>
      </function>
    </def>

Now Cppcheck will report an error:

    cppcheck --library=test.cfg formatstring.c
    Checking formatstring.c...
    [formatstring.c:3]: (error) do_something format string requires 2 parameters but only 1 is given.

The `type` attribute can be either:

- printf - format string follows the printf rules

- scanf - format string follows the scanf rules

##### Value range

The valid values can be defined. Imagine:

    void test()
    {
        do_something(1024);
    }

No error is reported for that:

    # cppcheck valuerange.c
    Checking valuerange.c...

A configuration file can be created that says that 1024 is out of bounds. For instance:

    <?xml version="1.0"?>
    <def>
      <function name="do_something">
        <arg nr="1">
          <valid>0:1023</valid>
        </arg>
      </function>
    </def>

Now Cppcheck will report an error:

    cppcheck --library=test.cfg range.c
    Checking range.c...
    [range.c:3]: (error) Invalid do_something() argument nr 1. The value is 1024 but the valid values are '0-1023'.

Some example expressions you can use in the valid element:

    0,3,5  => only values 0, 3 and 5 are valid
    -10:20  =>  all values between -10 and 20 are valid
    :0  =>  all values that are less or equal to 0 are valid
    0:  =>  all values that are greater or equal to 0 are valid
    0,2:32  =>  the value 0 and all values between 2 and 32 are valid

##### minsize

Some function arguments take a buffer. With minsize you can configure the min size of the buffer (in bytes, not elements). Imagine:

    void test()
    {
        char str[5];
        do_something(str,"12345");
    }

No error is reported for that:

    # cppcheck minsize.c
    Checking minsize.c...

A configuration file can for instance be created that says that the size of the buffer in argument 1 must be larger than the strlen of argument 2.For instance:

    <?xml version="1.0"?>
    <def>
      <function name="do_something">
        <arg nr="1">
          <minsize type="strlen" arg="2"/>
        </arg>
        <arg nr="2"/>
      </function>
    </def>

Now Cppcheck will report this error:

    cppcheck --library=1.cfg minsize.c
    Checking minsize.c...
    [minsize.c:4]: (error) Buffer is accessed out of bounds: str

There are different types of minsizes:

strlen

  buffer size must be larger than other arguments string length. Example: see strcpy configuration in std.cfg

argvalue

  buffer size must be larger than value in other argument. Example: see memset configuration in std.cfg

sizeof

  buffer size must be larger than other argument buffer size. Example: see memccpy configuration in posix.cfg

mul

  buffer size must be larger than multiplication result when multiplying values given in two other arguments. Typically one argument defines the element size and another element defines the number of elements. Example: see fread configuration in std.cfg

##### strz

This setting is not used by Cppcheck currently. But with this you can say that an argument must be a zero-terminated string.

    <?xml version="1.0"?>
    <def>
      <function name="do_something">
        <arg nr="1">
          <strz/>
        </arg>
      </function>
    </def>

#### noreturn

Cppcheck doesn't assume that functions always return. Here is an example code:

    void test(int x)
    {
        int data, buffer[1024];
        if (x == 1)
            data = 123;
        else
            ZeroMemory(buffer, sizeof(buffer));
        buffer[0] = data;  // <- error: data is uninitialized if x is not 1
    }

In theory, if `ZeroMemory` terminates the program then there is no bug. Cppcheck therefore reports no error:

    # cppcheck noreturn.c
    Checking noreturn.c...

However if you use `--check-library` and `--enable=information` you'll get this:

    # cppcheck --check-library --enable=information noreturn.c
    Checking noreturn.c...
    [noreturn.c:7]: (information) --check-library: Function ZeroMemory() should have <noreturn> configuration

If a proper `windows.cfg` is provided, the bug is detected:

    # cppcheck --library=windows.cfg noreturn.c
    Checking noreturn.c...
    [noreturn.c:8]: (error) Uninitialized variable: data

Here is a minimal `windows.cfg` file:

    <?xml version="1.0"?>
    <def>
      <function name="ZeroMemory">
        <noreturn>false</noreturn>
        <arg nr="1"/>
        <arg nr="2"/>
      </function>
    </def>

#### use-retval

As long as nothing else is specified, cppcheck assumes that ignoring the return value of a function is ok:

    bool test(const char* a, const char* b)
    {
        strcmp(a, b);  // <- bug: The call of strcmp does not have side-effects, but the return value is ignored.
        return true;
    }

In case `strcmp` has side effects, such as assigning the result to one of the parameters passed to it, nothing bad would happen:

    # cppcheck useretval.c
    Checking useretval.c...

If a proper `lib.cfg` is provided, the bug is detected:

    # cppcheck --library=lib.cfg --enable=warning useretval.c
    Checking useretval.c...
    [useretval.c:3]: (warning) Return value of function strcmp() is not used.

Here is a minimal `lib.cfg` file:

    <?xml version="1.0"?>
    <def>
      <function name="strcmp">
        <use-retval/>
        <arg nr="1"/>
        <arg nr="2"/>
      </function>
    </def>

#### pure and const

These correspond to the GCC function attributes pure and const.

A pure function has no effects except to return a value, and its return value depends only on the parameters and global variables.

A const function has no effects except to return a value, and its return value depends only on the parameters.

Here is an example code:

    void f(int x)
    {
        if (calculate(x) == 213) {

        } else if (calculate(x) == 213) {
             // unreachable code
        }
    }

If `calculate()` is a const function then the result of `calculate(x)` will be the same in both conditions, since the same parameter value is used.

Cppcheck normally assumes that the result might be different, and reports no warning for the code:

    # cppcheck const.c
    Checking const.c...

If a proper `const.cfg` is provided, the unreachable code is detected:

    # cppcheck --enable=style --library=const const.c
    Checking const.c...
    [const.c:7]: (style) Expression is always false because 'else if' condition matches previous condition at line 5.

Here is a minimal `const.cfg` file:

    <?xml version="1.0"?>
    <def>
      <function name="calculate">
        <const/>
        <arg nr="1"/>
      </function>
    </def>

#### Example configuration for strcpy()

The proper configuration for the standard strcpy() function would be:

      <function name="strcpy">
        <leak-ignore/>
        <noreturn>false</noreturn>
        <arg nr="1">
          <not-null/>
        </arg>
        <arg nr="2">
          <not-null/>
          <not-uninit/>
          <strz/>
        </arg>
      </function>

The `<leak-ignore/>` tells Cppcheck to ignore this function call in the leaks checking. Passing allocated memory to this function won't mean it will be deallocated.

The `<noreturn>` tells Cppcheck if this function returns or not.

The first argument that the function takes is a pointer. It must not be a null pointer, therefore `<not-null>` is used.

The second argument the function takes is a pointer. It must not be null. And it must point at initialized data. Using `<not-null>` and `<not-uninit>` is correct. Moreover it must point at a zero-terminated string so <strz> is also used.

### define

Libraries can be used to define preprocessor macros as well. For example:

    <?xml version="1.0"?>
    <def>
      <define name="NULL_VALUE" value="0"/>
    </def>

Each occurrence of "NULL_VALUE" in the code would then be replaced by "0" at preprocessor stage.

### podtype

Lots of code relies on typedefs providing platform independent types. "podtype"-tags can be used to provide necessary information to cppcheck to support them. Without further information, cppcheck does not understand the type "uint16_t" in the following example:

    void test() {
        uint16_t a;
    }

No message about variable 'a' being unused is printed:

    # cppcheck --enable=style unusedvar.cpp
    Checking unusedvar.cpp...

If uint16_t is defined in a library as follows, the result improves:

    <?xml version="1.0"?>
    <def>
      <podtype name="uint16_t" sign="u" size="2"/>
    </def>

The size of the type is specified in bytes. Possible values for the "sign" attribute are "s" (signed) and "u" (unsigned). Both attributes are optional. Using this library, cppcheck prints:

    # cppcheck --library=lib.cfg --enable=style unusedvar.cpp
    Checking unusedvar.cpp...
    [unusedvar.cpp:2]: (style) Unused variable: a

### container

A lot of C++ libraries, among those the STL itself, provide containers with very similar functionality. Libraries can be used to tell cppcheck about their behaviour. Each container needs a unique ID. It can optionally have a startPattern, which must be a valid Token::Match pattern and an endPattern that is compared to the linked token of the first token with such a link. The optional attribute "inherits" takes an ID from a previously defined container.

Inside the <container> tag, functions can be defined inside of the tags <size>, <access> and <other> (on your choice). Each of them can specify an action like "resize" and/or the result it yields, for example "end-iterator".

The following example provides a definition for std::vector, based on the definition of "stdContainer" (not shown):

    <?xml version="1.0"?>
    <def>
      <container id="stdVector" startPattern="std :: vector &lt;" inherits="stdContainer">
        <size>
          <function name="push_back" action="push"/>
          <function name="pop_back" action="pop"/>
        </size>
        <access indexOperator="array-like">
          <function name="at" yields="at_index"/>
          <function name="front" yields="item"/>
          <function name="back" yields="item"/>
        </access>
      </container>
    </def>

## Rules

You can define custom rules using regular expressions.

These rules can not perform sophisticated analysis of the code. But they give you an easy way to check for various simple patterns in the code.

To get started writing rules, see the related articles here:

http://sourceforge.net/projects/cppcheck/files/Articles/

The file format for rules is:

    <?xml version="1.0"?>
    <rule>
      <tokenlist>LIST</tokenlist>
      <pattern>PATTERN</pattern>
      <message>
        <id>ID</id>
        <severity>SEVERITY</severity>
        <summary>SUMMARY</summary>
      </message>
    </rule>

CDATA can be used to include characters in a pattern that might interfere with XML:

    <![CDATA[some<strange>pattern]]>

### <tokenlist>

The `<tokenlist>` element is optional. With this element you can control what tokens are checked. The `LIST` can be either `define`, `raw`, `normal` or `simple`.

define

  used to check #define preprocessor statements.

raw

  used to check the preprocessor output.

normal

  used to check the `normal` token list. There are some simplifications.

simple

  used to check the simple token list. All simplifications are used. Most Cppcheck checks use the simple token list.

If there is no <tokenlist> element then `simple` is used automatically.

### <pattern>

The `PATTERN` is the `PCRE`-compatible regular expression that will be executed.

### <id>

The ID specify the user-defined message id.

### <severity>

The `SEVERITY` must be one of the `Cppcheck` severities: `information`, `performance`, `portability`, `style`, `warning`, or `error`.

### <summary>

Optional. The summary for the message. If no summary is given, the matching tokens is written.

## Cppcheck addons

Cppcheck addons are implemented as standalone scripts or programs. With Cppcheck addons, you can for instance:

- add extra custom checkers that use sophisticated analysis

- visualize your code

- etc

### Using Cppcheck addons

Currently there are two steps to use an addon:

1. Run Cppcheck to generate dump files

2. Run the addon on the dump files

The `--dump` flag is used to generate dump files. To generate a dump file for every source file in the foo/ folder:

    cppcheck --dump foo/

To run a addon script on all dump files in the foo/ folder:

    python addon.py foo/*.dump

#### Where to find some Cppcheck addons

There are a few addons that can be downloaded.

- Addons provided by the Cppcheck project: http://github.com/danmar/cppcheck/blob/master/addons

- ublinter, a project that wants to "lint" for "undefined behaviour": http://github.com/danmar/ublinter

We would be happy to add a link to your addon here (no matter if it's commercial or free).

### Writing Cppcheck addons

Cppcheck generates dump files in XML format that contains:

- Token list

- Syntax trees

- Symbol database (functions, classes, variables, all scopes, ..)

- Known values (value flow analysis)

Cppcheck can't execute addons directly. There is no direct interface. This means there are not much restrictions:

- You can use any licensing you want for your addons

- You can use an arbitrary script/programming language to write addons

- The user interface and output is defined by you

- You can use addons for other use cases than generating warnings

For your convenience, Cppcheck provides cppcheckdata.py that you can use to access Cppcheck data from Python. Using this is optional.

#### Example 1 - print all tokens

Script:

    import sys
    import cppcheckdata

    def printtokens(data):
        for token in data.tokenlist:
            print(token.str)

    for arg in sys.argv[1:]:
        printtokens(cppcheckdata.parse(arg))

#### Example 2 - List all functions

Script:

    import sys
    import cppcheckdata

    def printfunctions(data):
        for scope in data.scopes:
            if scope.type == 'Function':
                print(scope.className)

    for arg in sys.argv[1:]:
        printfunctions(cppcheckdata.parse(arg))

#### Example 3 - List all classes

Script:

    import sys
    import cppcheckdata

    def printclasses(data):
        for scope in data.scopes:
            if scope.type == 'Class':
                print(scope.className)

    for arg in sys.argv[1:]:
        printfunctions(cppcheckdata.parse(arg))

## HTML report

You can convert the XML output from cppcheck into a HTML report. You'll need Python and the pygments module (http://pygments.org/) for this to work. In the Cppcheck source tree there is a folder `htmlreport` that contains a script that transforms a Cppcheck XML file into HTML output.

This command generates the help screen:

    htmlreport/cppcheck-htmlreport -h

The output screen says:

    Usage: cppcheck-htmlreport [options]

    Options:
      -h, --help      show this help message and exit
      --file=FILE     The cppcheck xml output file to read defects from.
                      Default is reading from stdin.
      --report-dir=REPORT_DIR
                      The directory where the html report content is written.
      --source-dir=SOURCE_DIR
                      Base directory where source code files can be found.

An example usage:

    ./cppcheck gui/test.cpp --xml 2> err.xml
    htmlreport/cppcheck-htmlreport --file=err.xml --report-dir=test1 --source-dir=.

## Graphical user interface

### Introduction

A Cppcheck GUI is available.

The main screen is shown immediately when the GUI is started.

### Check source code

Use the Check menu.

### Inspecting results

The results are shown in a list.

You can show/hide certain types of messages through the View menu.

Results can be saved to an XML file that can later be opened. See `Save results to file` and `Open XML`.

### Settings

The language can be changed at any time by using the Language menu.

More settings are available in Edit Preferences .

### Project files

The project files are used to store project specific settings. These settings are:

- include folders

- preprocessor defines

As you can read in chapter 3 in this manual the default is that Cppcheck checks all configurations. So only provide preprocessor defines if you want to limit the checking.