2009-10-11

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 index out of bounds

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

By default, only certain errors are reported. With "--all" you will get more reports. But beware - some messages may be wrong. Here is a simple code example: void f() { Fred *f = new Fred; } Execute this command: cppcheck --all file1.cpp The output from Cppcheck: [file1.cpp:4]: (possible error) Memory leak: fred The "possible" means that the reported message may be wrong (if Fred has automatic deallocation it is not a memory leak).

By default Cppcheck will only check for bugs. There are also a few checks for stylistic issues. Here is a simple code example: void f(int x) { int i; if (x == 0) { i = 0; } } To enable stylistic checks, use the --style flag: cppcheck --style file1.c The reported error is: [file3.c:3]: (style) The scope of the variable i can be limited

Many times you will want to save the results in a file. The results are written to stderr and the progress messages are written to stdout. So you can use the standard redirections to save to file. cppcheck file1.c 2> err.txt

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 --unused-functions 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 one of: error / possible error / style / possible style msg the error message in plain text 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. First you need to create a suppressions file. [error id]:[filename] [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/ 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 both increase the capabilities and also reduce the amount of false positives.

A common cause of false positives is when there is automatic deallocation. Here is an example: void Form1::foo() { QPushButton *pb = new QPushButton( "OK", this ); } Cppcheck can't see where the deallocation is when you have such code. If you execute: cppcheck --all file1.cpp The result will be: [file1.cpp:4]: (possible error) Memory leak: pb The "possible" in the error message means that the message may be a false positive. To avoid such false positives, create a textfile and write the names of the automaticly deallocated classes. QLabel QPushButton Then execute cppcheck with the --auto-dealloc option: cppcheck --auto-dealloc qt.lst file1.cpp

Cppcheck understands many common allocation and deallocation functions. But not all. Here is a trick to add custom checking. First we write simple implementations for the allocation and deallocation functions: 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. Here is an example program that uses CreateFred and DestroyFred: void foo(int x) { void *f = CreateFred(); if (x == 1) return; DestroyFred(f); } 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. We don'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 except.cpp The output will be: [except.cpp:3]: (style) Upon exception there is memory leak: a If an exception occurs when b is allocated, a will leak.