# Cppcheck 1.46

# Chapter 1. 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.

# Chapter 2. Getting started

## 2.1. 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

## 2.2. Checking all files in a folder

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

    cppcheck path

If "path" is a folder then cppcheck will check all sourcefiles in this folder.

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

## 2.3. Excluding a file or folder from checking

There is no command to exclude a file or folder from checking. But you can exclude a file or folder by being more careful when including files and folders in the checking.

Imagine for example that the folder "src" contain the folders "a", "b" and "c". To exclude "c" this command can be used:

    cppcheck src/a src/b

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

The flag `--file-list` might also be useful.

## 2.4. 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

## 2.5. Enable messages

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

### 2.5.1. Stylistic issues

With `--enable=style` you enable most `warning`, `style` and `performance` messages.

Here is a simple code example:

    void f(int x)
    {
        int i;
        if (x == 0)
        {
            i = 0;
        }
    }

There are no bugs in that code so Cppcheck won't report anything by default. To enable the stylistic messages, use the --enable=style command:

    cppcheck --enable=style file3.c

The output from Cppcheck is now:

    Checking file3.c...
    [file3.c:3]: (style) Variable 'i' is assigned a value that is never used
    [file3.c:3]: (style) The scope of the variable i can be reduced

### 2.5.2. Unused functions

This check will try to find unused functions. It is best to use this when the whole program is checked, so that all usages is seen by cppcheck.

    cppcheck --enable=unusedFunction path

### 2.5.3. Enable all checks

To enable all checks your can use the `--enable=all` flag:

    cppcheck --enable=all path

## 2.6. 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

## 2.7. Multithreaded checking

To use 4 threads to check the files in a folder:

    cppcheck -j 4 path

# Chapter 3. Preprocessor configurations

By default Cppcheck will check all preprocessor configurations (except those that have #error in them). This is the recommended behaviour.

But if you want to manually limit the checking you can do so with `-D`.

Beware that only the macros, which are given here and the macros defined in source files and known header files are considered. That excludes all the macros defined in some system header files, which are by default not examined by cppcheck.

The usage: if you, for example, want to limit the checking so the only configuration to check should be "DEBUG=1;__cplusplus" then something like this can be used:

    cppcheck -DDEBUG=1 -D__cplusplus path

# Chapter 4. XML output

Cppcheck can generate the output in XML format.

Use the --xml flag when you execute cppcheck:

    cppcheck --xml file1.cpp

The xml format is:

    <?xml version="1.0"?>
    <results>
      <error file="file1.cpp" line="123" id="someError"
                   severity="error" msg="some error text"/>
    </results>

Attributes:

file

  filename. Both relative and absolute paths are possible

line

  a number

id

  id of error. These are always valid symbolnames.

severity

  either `error` or `style`. `warning` and `performance` are saved as `style`.

msg

  the error message

# Chapter 5. 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

# Chapter 6. Suppressions

If you want to filter out certain errors you can suppress these. First you need to create a suppressions file. The format is:

    [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.

Here is an example:

    memleak:file1.cpp
    exceptNew:file1.cpp
    uninitvar

You can then use the suppressions file:

    cppcheck --suppressions suppressions.txt src/

# Chapter 7. Leaks

Looking for memory leaks and resource leaks is a key feature of Cppcheck. Cppcheck can detect many common mistakes by default. But through some tweaking you can improve the checking.

## 7.1. Userdefined allocation/deallocation functions

`Cppcheck` understands many common allocation and deallocation functions. But not all.

Here is example code that might leak memory or resources:

    void foo(int x)
    {
        void *f = CreateFred();
        if (x == 1)
            return;
        DestroyFred(f);
    }

If you analyse that with Cppcheck it won't find any leaks:

    cppcheck --enable=possibleError fred1.cpp

You can add some custom leaks checking by providing simple implementations for the allocation and deallocation functions. Write this in a separate file:

    void *CreateFred()
    {
        return malloc(100);
    }

    void DestroyFred(void *p)
    {
        free(p);
    }

When Cppcheck see this it understands that CreateFred will return allocated memory and that DestroyFred will deallocate memory.

Now, execute `Cppcheck` this way:

    cppcheck --append=fred.cpp fred1.cpp

The output from cppcheck is:

    Checking fred1.cpp...
    [fred1.cpp:5]: (error) Memory leak: f

# Chapter 8. Exception safety

Cppcheck has a few checks that ensure that you don't break the basic guarantee of exception safety. It doesn't have any checks for the strong guarantee yet.

Example:

    Fred::Fred() : a(new int[20]), b(new int[20])
    {
    }

By default cppcheck will not detect any problems in that code.

To enable the exception safety checking you can use `--enable`:

    cppcheck --enable=exceptNew --enable=exceptRealloc fred.cpp

The output will be:

    [fred.cpp:3]: (style) Upon exception there is memory leak: a

If an exception occurs when `b` is allocated, `a` will leak.

Here is another example:

    int *p;

    int a(int sz)
    {
        delete [] p;
        if (sz <= 0)
            throw std::runtime_error("size <= 0");
        p = new int[sz];
    }

Check that with Cppcheck:

    cppcheck --enable=exceptNew --enable=exceptRealloc except2.cpp

The output from Cppcheck is:

    [except2.cpp:7]: (error) Throwing exception in invalid state, p points at deallocated memory

# Chapter 9. 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=.

# Chapter 10. Graphical user interface

## 10.1. Introduction

A Cppcheck GUI is available.

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

## 10.2. Check source code

Use the `Check` menu.

## 10.3. 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`.

## 10.4. Settings

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

More settings are available in `Edit`>`Preferences`.

## 10.5. Project files

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

- include folders

- preprocessor defines

It isn't recommended to provide the paths to the standard C/C++ headers - Cppcheck has internal knowledge about ANSI C/C++ and it isn't recommended that this known functionality is redefined. But feel free to try it.

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.