man: Added writing-addons.md
This commit is contained in:
Daniel Marjamäki
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---
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title: Writing addons
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subtitle: Version 2.9
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author: Cppcheck team
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lang: en
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documentclass: report
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---
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# Introduction
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This document provides an overview about writing Cppcheck addons.
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# Overview of data
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## Tokens
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See class `Token` in cppcheckdata.py
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Cppcheck splits up the code in tokens. Operators, numbers, identifiers, etc.
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Example C code:
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ab = a + b;
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Addon code:
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import cppcheck
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@cppcheck.checker
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def func(cfg, data):
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for token in cfg.tokenlist:
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print(token.str)
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Output:
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$ cppcheck --dump test.c
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$ python3 runaddon.py myaddon.py test.c.dump
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Checking 1.c.dump...
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Checking 1.c.dump, config ...
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ab
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=
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a
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+
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b
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;
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There are various properties in the `Token` class and some of those will be discussed below.
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## AST - Abstract syntax tree
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Cppcheck creates a syntax tree for every expression.
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Example C code:
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ab = a + b;
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Addon code:
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import cppcheck
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@cppcheck.checker
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def func(cfg, data):
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for token in cfg.tokenlist:
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out = token.str
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if token.astParent:
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out += f' parent:"{token.astParent.str}"'
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if token.astOperand1:
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out += f' astOperand1:"{token.astOperand1.str}"'
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if token.astOperand2:
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out += f' astOperand2:"{token.astOperand2.str}"'
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print(out)
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Output:
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$ cppcheck --dump test.c
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$ python3 runaddon.py myaddon.py test.c.dump
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Checking 1.c.dump...
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Checking 1.c.dump, config ...
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ab parent:"="
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= astOperand1:"ab" astOperand2:"+"
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a parent:"+"
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+ parent:"=" astOperand1:"a" astOperand2:"b"
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b parent:"+"
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;
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## ValueType
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Data type of expressions are provided by `class ValueType` in cppcheckdata.py.
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Example C code:
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short a;
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a = a + 10;
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Addon code:
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import cppcheck
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@cppcheck.checker
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def func(cfg, data):
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for token in cfg.tokenlist:
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print(f'{token.str} : {token.valueType}')
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Output:
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$ cppcheck --dump test.c
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$ python3 runaddon.py myaddon.py test.c.dump
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Checking 1.c.dump...
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Checking 1.c.dump, config ...
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short : None
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a : ValueType(type='short', sign='signed', bits=0, typeScopeId=None, originalTypeName=None, constness=0, pointer=0)
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; : None
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a : ValueType(type='short', sign='signed', bits=0, typeScopeId=None, originalTypeName=None, constness=0, pointer=0)
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= : ValueType(type='short', sign='signed', bits=0, typeScopeId=None, originalTypeName=None, constness=0, pointer=0)
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a : ValueType(type='short', sign='signed', bits=0, typeScopeId=None, originalTypeName=None, constness=0, pointer=0)
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+ : ValueType(type='int', sign='signed', bits=0, typeScopeId=None, originalTypeName=None, constness=0, pointer=0)
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10 : ValueType(type='int', sign='signed', bits=0, typeScopeId=None, originalTypeName=None, constness=0, pointer=0)
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; : None
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The `pointer` property is a simple counter.
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int p => pointer=0
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int *p => pointer=1
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int **p => pointer=2
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The `constness` property is a bitmask.
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int * * => constness=0
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const int * * => constness=1
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int * const * => constness=2
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int * * const => constness=4
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const int * const * => constness=3
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const int * const * const => constness=7
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## Variable
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Information about a variable is provided by `class Variable` in cppcheckdata.py.
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Example code:
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short a[10];
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a[0] = 0;
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Addon code:
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import cppcheck
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@cppcheck.checker
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def func(cfg, data):
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for token in cfg.tokenlist:
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print(f'{token.str} : {token.variable}')
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Output:
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$ cppcheck --dump test.c
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$ python3 runaddon.py myaddon.py test.c.dump
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Checking 1.c.dump...
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Checking 1.c.dump, config ...
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a : Variable(Id='0x55f432fc1580', nameTokenId='0x55f432fe0850', typeStartTokenId='0x55f432fc0eb0', typeEndTokenId='0x55f432fc0eb0', access='Global', scopeId='0x55f432fe0360', isArgument=False, isArray=True, isClass=False, isConst=False, isGlobal=True, isExtern=False, isLocal=False, isPointer=False, isReference=False, isStatic=False, constness=0)
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[ : None
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10 : None
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] : None
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; : None
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a : Variable(Id='0x55f432fc1580', nameTokenId='0x55f432fe0850', typeStartTokenId='0x55f432fc0eb0', typeEndTokenId='0x55f432fc0eb0', access='Global', scopeId='0x55f432fe0360', isArgument=False, isArray=True, isClass=False, isConst=False, isGlobal=True, isExtern=False, isLocal=False, isPointer=False, isReference=False, isStatic=False, constness=0)
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[ : None
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0 : None
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] : None
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= : None
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0 : None
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; : None
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## Scope
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See `class Scope` in cppcheckdata.py.
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Every token is in some scope.
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If you see {} in the code then that is a scope of some kind. There is one scope that is not surrounded by {}; the global scope.
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Example c code:
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int x;
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void foo()
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{
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if (x)
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{
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x = 0;
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}
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}
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Example addon #1 (list all scopes):
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import cppcheck
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@cppcheck.checker
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def func(cfg, data):
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for scope in cfg.scopes:
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print(scope.type)
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Output:
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$ cppcheck --dump test.c
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$ python3 runaddon.py myaddon.py test.c.dump
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Checking 1.c.dump...
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Checking 1.c.dump, config ...
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Global
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Function
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If
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Example addon #2 (show scope for each token):
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import cppcheck
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@cppcheck.checker
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def func(cfg, data):
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for token in cfg.tokenlist:
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print(f'{token.str} : {scope.type}')
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Output:
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$ cppcheck --dump test.c
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$ python3 runaddon.py myaddon.py test.c.dump
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Checking 1.c.dump...
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Checking 1.c.dump, config ...
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int : Global
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x : Global
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; : Global
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void : Global
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foo : Global
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( : Global
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) : Global
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{ : Function
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if : Function
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( : Function
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x : Function
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) : Function
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{ : If
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x : If
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= : If
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0 : If
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; : If
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} : If
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} : Function
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### Special tokenlist tweaks and else if
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The cfg.tokenlist has some tweaks. In C/C++ code it is optional to use `{` and `}` around the conditional code,
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if the conditional code is only a single statement. However Cppcheck adds "{" and "}" tokens if those are missing.
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One more tweak is that in cfg.tokenlist there is no "else if" scope.
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Example C code:
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void foo(int x)
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{
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if (x > 0)
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--x;
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else if (x < 0)
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++x;
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}
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The tokens in the cfg.tokenlist will look like this:
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void foo(int x)
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{
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if (x > 0)
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{
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--x;
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}
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else
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{
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if (x < 0)
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{
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++x;
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}
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}
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}
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And there are 2 "If" scopes here. And 1 "Else" scope.
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## Function
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The class `Function` in cppcheckdata.py represents a function that is declared somewhere.
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Example code:
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void foo(int x);
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void bar()
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{
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foo(1);
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}
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Example addon #1:
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import cppcheck
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@cppcheck.checker
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def func(cfg, data):
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for token in cfg.tokenlist:
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print(f'{token.str} : {token.function}')
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Output:
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void : None
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foo : Function(Id='0x55c5f9330f60', tokenId='0', tokenDefId='0x55c5f93510d0', name='foo', type='Function', isVirtual=False, isImplicitlyVirtual=False, isInlineKeyword=False, isStatic=False, argumentId={1: '0x55c5f9351260'})
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( : None
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int : None
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x : None
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) : None
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; : None
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void : None
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bar : Function(Id='0x55c5f9331040', tokenId='0x55c5f93314a0', tokenDefId='0x55c5f93314a0', name='bar', type='Function', isVirtual=False, isImplicitlyVirtual=False, isInlineKeyword=False, isStatic=False, argumentId={})
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( : None
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) : None
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{ : None
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foo : Function(Id='0x55c5f9330f60', tokenId='0', tokenDefId='0x55c5f93510d0', name='foo', type='Function', isVirtual=False, isImplicitlyVirtual=False, isInlineKeyword=False, isStatic=False, argumentId={1: '0x55c5f9351260'})
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( : None
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1 : None
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) : None
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; : None
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} : None
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## Value flow
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For Cppcheck, by default variables and expressions have "unknown" values. If the value is only constrained by the data type that is typically not enough information to write warnings with precision. Unless all the values possible in the data type are bad.
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In Cppcheck terminology an expression will have a "possible" value if Cppcheck can determine that there will be a specific value in some control flow paths.
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In Cppcheck terminology an expression will have a "known" value if Cppcheck can determine that there will be a specific value in all control flow paths.
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An expression can have several "possible" values. But it can't have several "known" values.
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Example code:
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void foo(int x) // <- values of x is only constrained by data type. there are no "possible" or "known" values here.
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{
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a = x; // <- assuming that condition below is not redundant, x can have value 2.
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if (x == 2)
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{
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b = x + 2; // <- value of x is always 2 when this code is executed. It's "known".
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}
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else
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{
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c = x;
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}
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d = x + 10; // <- value of x can be 2 when this code is executed. It's "possible".
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}
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Addon:
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import cppcheck
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@cppcheck.checker
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def func(cfg, data):
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for token in cfg.tokenlist:
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if token.values:
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print(f'line {token.linenr} str="{token.str}"')
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for value in token.values:
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print(f' {value}')
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Output:
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$ ../cppcheck --dump 1.c ; python3 runaddon.py myaddon.py 1.c.dump
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Checking 1.c ...
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Checking 1.c.dump...
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Checking 1.c.dump, config ...
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line 3 str="="
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Value(intvalue=2, tokvalue=None, floatvalue=None, containerSize=None, condition=4, valueKind='possible', inconclusive=False)
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line 3 str="x"
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Value(intvalue=2, tokvalue=None, floatvalue=None, containerSize=None, condition=4, valueKind='possible', inconclusive=False)
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line 4 str="2"
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Value(intvalue=2, tokvalue=None, floatvalue=None, containerSize=None, condition=None, valueKind='known', inconclusive=False)
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line 6 str="="
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Value(intvalue=4, tokvalue=None, floatvalue=None, containerSize=None, condition=4, valueKind='known', inconclusive=False)
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line 6 str="x"
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Value(intvalue=2, tokvalue=None, floatvalue=None, containerSize=None, condition=4, valueKind='known', inconclusive=False)
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line 6 str="+"
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Value(intvalue=4, tokvalue=None, floatvalue=None, containerSize=None, condition=4, valueKind='known', inconclusive=False)
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line 6 str="2"
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Value(intvalue=2, tokvalue=None, floatvalue=None, containerSize=None, condition=None, valueKind='known', inconclusive=False)
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line 12 str="="
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Value(intvalue=12, tokvalue=None, floatvalue=None, containerSize=None, condition=4, valueKind='possible', inconclusive=False)
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line 12 str="x"
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Value(intvalue=2, tokvalue=None, floatvalue=None, containerSize=None, condition=4, valueKind='possible', inconclusive=False)
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line 12 str="+"
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Value(intvalue=12, tokvalue=None, floatvalue=None, containerSize=None, condition=4, valueKind='possible', inconclusive=False)
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line 12 str="10"
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Value(intvalue=10, tokvalue=None, floatvalue=None, containerSize=None, condition=None, valueKind='known', inconclusive=False)
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If the value is determined from a condition then the attribute `condition` points out the line that has the condition.
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