]> 2011-02-06 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.

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

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

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

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 information Informational messages that might be interesting. Ignore these messages unless you really agree. The performance messages are based on 'common knowledge'. It is not certain that fixing performance messages will make any measurable difference in speed. Fixing performance messages generally doesn't make your code more readable.

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

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

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

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

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

To use 4 threads to check the files in a folder: cppcheck -j 4 path

By default Cppcheck will check all preprocessor configurations (except those that has #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 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 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 If you want to filter out certain errors you can suppress these. The --suppress= command line option is used to specify suppressions on the command line. The format 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. cppcheck --suppress=memleak:file1.cpp src/ If you have more than a couple of suppressions, create a suppressions file with one line per suppression as above. Here is an example: memleak:file1.cpp exceptNew:file1.cpp uninitvar You can then use the suppressions file: cppcheck --suppressions suppressions.txt src/ 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.

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

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 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=.

A Cppcheck GUI is available. The main screen is shown immediately when the GUI is started.

Use the Check menu.

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.

The language can be changed at any time by using the Language menu. More settings are available in EditPreferences .

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.

Daniel Marjamäki Cppcheck 2010-2011 &writing-rules-1; &writing-rules-2; &writing-rules-3; &cppcheck-design;