# Cppcheck 1.67

2014-09-28

## 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. Cppcheck only 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.

Accuracy

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

### 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 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

### 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

### 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

  Informational messages about checking problems.

### 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 information messages
    cppcheck --enable=warning,information 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. And 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

## Preprocessor configurations

By default Cppcheck will check all preprocessor configurations (except those that have #error in them).

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.

## XML output

Cppcheck can generate the output in `XML` format. There is an old `XML` format (version 1) and a new `XML` format (version 2). Please use the new version if you can.

The old version is kept for backwards compatibility only. It will not be changed. But it will likely be removed someday. Use `--xml` to enable this format.

The new version fixes a few problems with the old format. The new format will probably be updated in future versions of cppcheck with new attributes and elements. A sample command to check a file and output errors in the new `XML` format:

    cppcheck --xml-version=2 file1.cpp

Here is a sample version 2 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">
          <location file="file.c" 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.

### 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

`line`

  a number

`msg`

  this attribute doesn't exist yet. But in the future we may add a short message for each location.

## 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

  severity

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

## 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 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 windows/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.

If you create 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.

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

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 windows 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 windows 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>

### Function argument: 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 windows configuration file then Cppcheck detects the bug:

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

Here is the minimal `windows.cfg`:

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

### Function Argument: 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 windows configuration file then `Cppcheck` detects the bug:

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

Here is a minimal `windows.cfg` file:

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

### Function Argument: 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">
        <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.

### Function Argument: 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'.

### 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>
      </function>
    </def>

### use-retval

Per default, 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...
    [noreturn.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/>
      </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/>
        </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.

### Specifications for all arguments

Specifying `-1` as the argument number is going to apply a check to all arguments of that function. The specifications for individual arguments override this setting.

## 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 extensions with Python

Using dump files it is possible to write Cppcheck extensions with for instance Python.

The `cppcheckdata.py` module (`http://github.com/danmar/cppcheck/blob/master/tools/cppcheckdata.py`) allows you to load such dump file. It contains `Token`/`Variable`/`ValueFlow.Value`/`Scope` classes that are similar to the `C++` classes in `Cppcheck`-core. The doxygen information for the `C++` classes should be somewhat useful for Python developers also.

### Simple checker: Division by zero

Here is a simple checker:

    import cppcheckdata

    data = cppcheckdata.parsedump('1.c.dump')

    for token in data.tokenlist:
        if token.str == '/' or token.str == '%':
            # Get denominator (2nd operand)
            den = token.astOperand2

            # Can denominator be zero?
            if den.getValue(0):
                print '[' + token.file + ':' + str(token.linenr) + '] Division by zero'

Example usage:

    cppcheck --dump 1.c
    python divzero.py

### Licensing

The dump file is just a xml file, so it is an open interface without restrictions. You can use it in any way you need.

The `cppcheckdata.py` is also free to use. No matter if your project is open source or closed source. Use it for any purpose.

## 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.