cppcheck/lib/checknullpointer.cpp

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/*
* Cppcheck - A tool for static C/C++ code analysis
* Copyright (C) 2007-2010 Daniel Marjamäki and Cppcheck team.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
//---------------------------------------------------------------------------
#include "checknullpointer.h"
#include "executionpath.h"
#include "mathlib.h"
//---------------------------------------------------------------------------
// Register this check class (by creating a static instance of it)
namespace
{
CheckNullPointer instance;
}
//---------------------------------------------------------------------------
/**
* @brief parse a function call and extract information about variable usage
* @param tok first token
* @param var variables that the function read / write.
* @param value 0 => invalid with null pointers as parameter.
* 1-.. => invalid with uninitialized data.
*/
void CheckNullPointer::parseFunctionCall(const Token &tok, std::list<const Token *> &var, unsigned char value)
{
// standard functions that dereference first parameter..
// both uninitialized data and null pointers are invalid.
static std::set<std::string> functionNames1;
if (functionNames1.empty())
{
functionNames1.insert("memchr");
functionNames1.insert("memcmp");
functionNames1.insert("strcat");
functionNames1.insert("strncat");
functionNames1.insert("strchr");
functionNames1.insert("strrchr");
functionNames1.insert("strcmp");
functionNames1.insert("strncmp");
functionNames1.insert("strdup");
functionNames1.insert("strndup");
functionNames1.insert("strlen");
functionNames1.insert("strstr");
}
// standard functions that dereference second parameter..
// both uninitialized data and null pointers are invalid.
static std::set<std::string> functionNames2;
if (functionNames2.empty())
{
functionNames2.insert("memcmp");
functionNames2.insert("memcpy");
functionNames2.insert("memmove");
functionNames2.insert("strcat");
functionNames2.insert("strncat");
functionNames2.insert("strcmp");
functionNames2.insert("strncmp");
functionNames2.insert("strcpy");
functionNames2.insert("strncpy");
functionNames2.insert("strstr");
}
// 1st parameter..
if ((Token::Match(&tok, "%var% ( %var% ,|)") && tok.tokAt(2)->varId() > 0) ||
(value == 0 && Token::Match(&tok, "%var% ( 0 ,|)")))
{
if (functionNames1.find(tok.str()) != functionNames1.end())
var.push_back(tok.tokAt(2));
else if (value == 0 && Token::Match(&tok, "memchr|memcmp|memcpy|memmove|memset|strcpy|printf|sprintf|snprintf"))
var.push_back(tok.tokAt(2));
else if (Token::simpleMatch(&tok, "fflush"))
var.push_back(tok.tokAt(2));
}
// 2nd parameter..
if ((Token::Match(&tok, "%var% ( %any% , %var% ,|)") && tok.tokAt(4)->varId() > 0) ||
(value == 0 && Token::Match(&tok, "%var% ( %any% , 0 ,|)")))
{
if (functionNames2.find(tok.str()) != functionNames2.end())
var.push_back(tok.tokAt(4));
}
}
/**
* Is there a pointer dereference? Everything that should result in
* a nullpointer dereference error message will result in a true
* return value. If it's unknown if the pointer is dereferenced false
* is returned.
* @param tok token for the pointer
* @param unknown it is not known if there is a pointer dereference (could be reported as a debug message)
* @return true => there is a dereference
*/
bool CheckNullPointer::isPointerDeRef(const Token *tok, bool &unknown)
{
unknown = false;
// Dereferencing pointer..
if (Token::Match(tok->tokAt(-3), "!!sizeof [;{}=+-/(,] * %var%"))
return true;
if (!Token::simpleMatch(tok->tokAt(-2), "& (") && tok->strAt(-1) != "&" && tok->strAt(-1) != "&&" && Token::Match(tok->next(), ". %var%"))
return true;
if (Token::Match(tok->previous(), "[;{}=+-/(,] %var% ["))
return true;
if (Token::Match(tok->previous(), "return %var% ["))
return true;
if (Token::Match(tok, "%var% ("))
return true;
if (Token::Match(tok, "%var% = %var% .") &&
tok->varId() > 0 &&
tok->varId() == tok->tokAt(2)->varId())
return true;
// Not a dereference..
if (Token::Match(tok->previous(), "[;{}] %var% ="))
return false;
// unknown if it's a dereference
unknown = true;
// assume that it's not a dereference (no false positives)
return false;
}
bool CheckNullPointer::isPointer(const unsigned int varid)
{
// Check if given variable is a pointer
const Token *tok = Token::findmatch(_tokenizer->tokens(), "%varid%", varid);
tok = tok->tokAt(-2);
// maybe not a pointer
if (!Token::Match(tok, "%type% * %varid% [;)=]", varid))
return false;
// it is a pointer
if (!tok->previous() ||
Token::Match(tok->previous(), "[({};]") ||
tok->previous()->isName())
{
return true;
}
// it is not a pointer
return false;
}
void CheckNullPointer::nullPointerAfterLoop()
{
// Locate insufficient null-pointer handling after loop
for (const Token *tok = _tokenizer->tokens(); tok; tok = tok->next())
{
// only interested in while ( %var% )
// TODO: Aren't there false negatives. Shouldn't other loops be handled such as:
// - while ( ! %var% )
// - while ( %var% && .. )
if (! Token::Match(tok, "while ( %var% )"))
continue;
// Get variable id for the loop variable
const unsigned int varid(tok->tokAt(2)->varId());
if (varid == 0)
continue;
// Get variable name for the loop variable
const std::string varname(tok->strAt(2));
// Locate the end of the while loop body..
const Token *tok2 = tok->tokAt(4)->link();
// Check if the variable is dereferenced after the while loop
while (0 != (tok2 = tok2 ? tok2->next() : 0))
{
// Don't check into inner scopes or outer scopes. Stop checking if "break" is found
if (tok2->str() == "{" || tok2->str() == "}" || tok2->str() == "break")
break;
// loop variable is found..
if (tok2->varId() == varid)
{
// dummy variable.. is it unknown if pointer is dereferenced or not?
bool unknown = false;
// Is the loop variable dereferenced?
if (CheckNullPointer::isPointerDeRef(tok2, unknown))
{
// Is loop variable a pointer?
if (isPointer(varid))
nullPointerError(tok2, varname);
}
break;
}
}
}
}
void CheckNullPointer::nullPointerLinkedList()
{
// looping through items in a linked list in a inner loop.
// Here is an example:
// for (const Token *tok = tokens; tok; tok = tok->next) {
// if (tok->str() == "hello")
// tok = tok->next; // <- tok might become a null pointer!
// }
for (const Token *tok1 = _tokenizer->tokens(); tok1; tok1 = tok1->next())
{
// search for a "for" token..
if (!Token::simpleMatch(tok1, "for ("))
continue;
// is there any dereferencing occurring in the for statement
// parlevel2 counts the parantheses when using tok2.
unsigned int parlevel2 = 1;
for (const Token *tok2 = tok1->tokAt(2); tok2; tok2 = tok2->next())
{
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// Parentheses..
if (tok2->str() == "(")
++parlevel2;
else if (tok2->str() == ")")
{
if (parlevel2 <= 1)
break;
--parlevel2;
}
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// Dereferencing a variable inside the "for" parentheses..
else if (Token::Match(tok2, "%var% . %var%"))
{
// Variable id for dereferenced variable
const unsigned int varid(tok2->varId());
if (varid == 0)
continue;
if (Token::Match(tok2->tokAt(-2), "%varid% ?", varid))
continue;
// Variable name of dereferenced variable
const std::string varname(tok2->str());
// Check usage of dereferenced variable in the loop..
unsigned int indentlevel3 = 0;
for (const Token *tok3 = tok1->next()->link(); tok3; tok3 = tok3->next())
{
if (tok3->str() == "{")
++indentlevel3;
else if (tok3->str() == "}")
{
if (indentlevel3 <= 1)
break;
--indentlevel3;
}
// TODO: are there false negatives for "while ( %varid% ||"
else if (Token::Match(tok3, "while ( %varid% &&|)", varid))
{
// Make sure there is a "break" or "return" inside the loop.
// Without the "break" a null pointer could be dereferenced in the
// for statement.
// indentlevel4 is a counter for { and }. When scanning the code with tok4
unsigned int indentlevel4 = indentlevel3;
for (const Token *tok4 = tok3->next()->link(); tok4; tok4 = tok4->next())
{
if (tok4->str() == "{")
++indentlevel4;
else if (tok4->str() == "}")
{
if (indentlevel4 <= 1)
{
// Is this variable a pointer?
if (isPointer(varid))
nullPointerError(tok1, varname, tok3->linenr());
break;
}
--indentlevel4;
}
// There is a "break" or "return" inside the loop.
// TODO: there can be false negatives. There could still be
// execution paths that are not properly terminated
else if (tok4->str() == "break" || tok4->str() == "return")
break;
}
}
}
}
}
}
}
void CheckNullPointer::nullPointerStructByDeRefAndChec()
{
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// Dereferencing a struct pointer and then checking if it's NULL..
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// skipvar: don't check vars that has been tested against null already
std::set<unsigned int> skipvar;
skipvar.insert(0);
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// Scan through all tokens
for (const Token *tok1 = _tokenizer->tokens(); tok1; tok1 = tok1->next())
{
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// Checking if some pointer is null.
// then add the pointer to skipvar => is it known that it isn't NULL
if (Token::Match(tok1, "if|while ( !| %var% )"))
{
tok1 = tok1->tokAt(2);
if (tok1->str() == "!")
tok1 = tok1->next();
skipvar.insert(tok1->varId());
continue;
}
// dereference in assignment
if (Token::Match(tok1, "[{};] %var% = %var% . %var%"))
{
if (std::string(tok1->strAt(1)) == tok1->strAt(3))
continue;
tok1 = tok1->tokAt(3);
}
// dereference in function call
else if (Token::Match(tok1->tokAt(-2), "%var% ( %var% . %var%") ||
Token::Match(tok1->previous(), ", %var% . %var%"))
{
// Is the function return value taken by the pointer?
bool assignment = false;
const unsigned int varid1(tok1->varId());
if (varid1 == 0)
continue;
const Token *tok2 = tok1->previous();
while (tok2 && !Token::Match(tok2, "[;{}]"))
{
if (Token::Match(tok2, "%varid% =", varid1))
{
assignment = true;
break;
}
tok2 = tok2->previous();
}
if (assignment)
continue;
}
// Goto next token
else
{
continue;
}
// struct dereference was found - investigate if it is later
// checked that it is not NULL
const unsigned int varid1(tok1->varId());
if (skipvar.find(varid1) != skipvar.end())
continue;
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// name of struct pointer
const std::string varname(tok1->str());
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// count { and } using tok2
unsigned int indentlevel2 = 0;
for (const Token *tok2 = tok1->tokAt(3); tok2; tok2 = tok2->next())
{
if (tok2->str() == "{")
++indentlevel2;
else if (tok2->str() == "}")
{
if (indentlevel2 <= 1)
break;
--indentlevel2;
}
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// label. goto destination..
else if (tok2->isName() && Token::simpleMatch(tok2->next(), ":"))
break;
// Reassignment of the struct
else if (tok2->varId() == varid1)
{
if (tok2->next()->str() == "=")
break;
if (Token::Match(tok2->tokAt(-2), "[,(] &"))
break;
}
// Loop..
/** @todo don't bail out if the variable is not used in the loop */
else if (tok2->str() == "do")
break;
// return at base level => stop checking
else if (indentlevel2 == 0 && tok2->str() == "return")
break;
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// Check if pointer is null.
// TODO: false negatives for something like: "if (p &&.."?
else if (Token::Match(tok2, "if ( !| %varid% )", varid1))
{
// Is this variable a pointer?
if (isPointer(varid1))
nullPointerError(tok1, varname, tok2->linenr());
break;
}
}
}
}
void CheckNullPointer::nullPointerByDeRefAndChec()
{
// Dereferencing a pointer and then checking if it's NULL..
for (const Token *tok = _tokenizer->tokens(); tok; tok = tok->next())
{
if (tok->str() == "if" && Token::Match(tok->previous(), "; if ( ! %var% )"))
{
const unsigned int varid(tok->tokAt(3)->varId());
if (varid == 0)
continue;
const std::string varname(tok->strAt(3));
// Check that variable is a pointer..
if (!isPointer(varid))
continue;
const Token * const decltok = Token::findmatch(_tokenizer->tokens(), "%varid%", varid);
for (const Token *tok1 = tok->previous(); tok1 && tok1 != decltok; tok1 = tok1->previous())
{
if (tok1->str() == ")" && Token::Match(tok1->link()->tokAt(-3), "%varid% = %var%", varid))
{
break;
}
if (tok1->varId() == varid)
{
bool unknown = false;
if (Token::Match(tok1->tokAt(-2), "%varid% = %varid% .", varid))
{
break;
}
else if (CheckNullPointer::isPointerDeRef(tok1, unknown))
{
nullPointerError(tok1, varname, tok->linenr());
break;
}
else if (Token::simpleMatch(tok1->previous(), "&"))
{
break;
}
else if (Token::simpleMatch(tok1->next(), "="))
{
break;
}
}
else if (tok1->str() == "{" ||
tok1->str() == "}")
break;
// label..
else if (Token::Match(tok1, "%type% :"))
break;
}
}
}
}
void CheckNullPointer::nullPointerByCheckAndDeRef()
{
// Check if pointer is NULL and then dereference it..
std::set<unsigned int> pointerVariables;
for (const Token *tok = _tokenizer->tokens(); tok; tok = tok->next())
{
if (Token::Match(tok, "* %var% [;,)=]"))
pointerVariables.insert(tok->next()->varId());
else if (Token::Match(tok, "if ("))
{
const Token *vartok = 0;
if (Token::Match(tok, "if ( ! %var% ) {"))
vartok = tok->tokAt(3);
else if (Token::Match(tok, "if ( NULL|0 == %var% ) {"))
vartok = tok->tokAt(4);
else if (Token::Match(tok, "if ( %var% == NULL|0 ) {"))
vartok = tok->tokAt(2);
else
continue;
bool null = true;
const unsigned int varid(vartok->varId());
if (varid == 0)
continue;
if (pointerVariables.find(varid) == pointerVariables.end())
continue;
// Name of the pointer
const std::string &pointerName = vartok->str();
unsigned int indentlevel = 1;
for (const Token *tok2 = tok->next()->link()->tokAt(2); tok2; tok2 = tok2->next())
{
if (tok2->str() == "{")
++indentlevel;
else if (tok2->str() == "}")
{
if (indentlevel == 0)
break;
--indentlevel;
if (null && indentlevel == 0)
{
// skip all "else" blocks because they are not executed in this execution path
while (Token::Match(tok2, "} else {"))
tok2 = tok2->tokAt(2)->link();
null = false;
}
}
if (Token::Match(tok2, "goto|return|continue|break|throw|if"))
{
if (Token::Match(tok2, "return * %varid%", varid))
nullPointerError(tok2, tok->strAt(3));
break;
}
// parameters to sizeof are not dereferenced
if (Token::Match(tok2, "decltype|sizeof ("))
{
tok2 = tok2->next()->link();
continue;
}
// calling unknown function (abort/init)..
if (Token::simpleMatch(tok2, ") ;") &&
Token::Match(tok2->link()->tokAt(-2), "[;{}] %var% ("))
{
break;
}
if (tok2->varId() == varid)
{
bool unknown = false;
if (Token::Match(tok2->previous(), "[;{}=] %var% = 0 ;"))
;
else if (CheckNullPointer::isPointerDeRef(tok2, unknown))
nullPointerError(tok2, pointerName);
else
break;
}
}
}
}
}
void CheckNullPointer::nullPointer()
{
nullPointerAfterLoop();
nullPointerLinkedList();
nullPointerStructByDeRefAndChec();
nullPointerByDeRefAndChec();
nullPointerByCheckAndDeRef();
}
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/** Dereferencing null constant (simplified token list) */
void CheckNullPointer::nullConstantDereference()
{
// this is kept at 0 for all scopes that are not executing
unsigned int indentlevel = 0;
for (const Token *tok = _tokenizer->tokens(); tok; tok = tok->next())
{
// start of executable scope..
if (indentlevel == 0 && Token::Match(tok, ") const| {"))
indentlevel = 1;
else if (indentlevel >= 1)
{
if (tok->str() == "{")
++indentlevel;
else if (tok->str() == "}")
{
if (indentlevel <= 2)
indentlevel = 0;
else
--indentlevel;
}
if (tok->str() == "(" && Token::Match(tok->previous(), "sizeof|decltype"))
tok = tok->link();
else if (Token::simpleMatch(tok, "exit ( )"))
{
// Goto end of scope
while (tok && tok->str() != "}")
{
if (tok->str() == "{")
tok = tok->link();
tok = tok->next();
}
if (!tok)
break;
}
else if (Token::simpleMatch(tok, "* 0"))
{
if (Token::Match(tok->previous(), "[<>;{}=+-*/(,]") ||
Token::Match(tok->previous(), "return|<<"))
{
nullPointerError(tok);
}
}
else if (indentlevel > 0 && Token::Match(tok, "%var% ("))
{
std::list<const Token *> var;
parseFunctionCall(*tok, var, 0);
// is one of the var items a NULL pointer?
for (std::list<const Token *>::const_iterator it = var.begin(); it != var.end(); ++it)
{
if ((*it)->str() == "0")
{
nullPointerError(*it);
}
}
}
}
}
}
/// @addtogroup Checks
/// @{
/**
* @brief %Check for null pointer usage (using ExecutionPath)
*/
class Nullpointer : public ExecutionPath
{
public:
/** Startup constructor */
Nullpointer(Check *c) : ExecutionPath(c, 0), null(false)
{
}
private:
/** Create checking of specific variable: */
Nullpointer(Check *c, const unsigned int id, const std::string &name)
: ExecutionPath(c, id),
varname(name),
null(false)
{
}
/** Copy this check */
ExecutionPath *copy()
{
return new Nullpointer(*this);
}
/** no implementation => compiler error if used by accident */
void operator=(const Nullpointer &);
/** is other execution path equal? */
bool is_equal(const ExecutionPath *e) const
{
const Nullpointer *c = static_cast<const Nullpointer *>(e);
return (varname == c->varname && null == c->null);
}
/** variable name for this check (empty => dummy check) */
const std::string varname;
/** is this variable null? */
bool null;
/** variable is set to null */
static void setnull(std::list<ExecutionPath *> &checks, const unsigned int varid)
{
std::list<ExecutionPath *>::iterator it;
for (it = checks.begin(); it != checks.end(); ++it)
{
Nullpointer *c = dynamic_cast<Nullpointer *>(*it);
if (c && c->varId == varid)
c->null = true;
}
}
/**
* Dereferencing variable. Check if it is safe (if the variable is null there's an error)
* @param checks Checks
* @param tok token where dereferencing happens
*/
static void dereference(std::list<ExecutionPath *> &checks, const Token *tok)
{
const unsigned int varid(tok->varId());
std::list<ExecutionPath *>::iterator it;
for (it = checks.begin(); it != checks.end(); ++it)
{
Nullpointer *c = dynamic_cast<Nullpointer *>(*it);
if (c && c->varId == varid && c->null)
{
CheckNullPointer *checkNullPointer = dynamic_cast<CheckNullPointer *>(c->owner);
if (checkNullPointer)
{
checkNullPointer->nullPointerError(tok, c->varname);
return;
}
}
}
}
/** parse tokens */
const Token *parse(const Token &tok, std::list<ExecutionPath *> &checks) const
{
if (Token::Match(tok.previous(), "[;{}] const| %type% * %var% ;"))
{
const Token * vartok = tok.tokAt(2);
if (tok.str() == "const")
vartok = vartok->next();
if (vartok->varId() != 0)
checks.push_back(new Nullpointer(owner, vartok->varId(), vartok->str()));
return vartok->next();
}
// Template pointer variable..
if (Token::Match(tok.previous(), "[;{}] %type% ::|<"))
{
const Token * vartok = &tok;
while (Token::Match(vartok, "%type% ::"))
vartok = vartok->tokAt(2);
if (Token::Match(vartok, "%type% < %type%"))
{
vartok = vartok->tokAt(3);
while (vartok && (vartok->str() == "*" || vartok->isName()))
vartok = vartok->next();
}
if (vartok
&& (vartok->str() == ">" || vartok->isName())
&& Token::Match(vartok->next(), "* %var% ;|="))
{
vartok = vartok->tokAt(2);
checks.push_back(new Nullpointer(owner, vartok->varId(), vartok->str()));
if (Token::simpleMatch(vartok->next(), "= 0 ;"))
setnull(checks, vartok->varId());
return vartok->next();
}
}
if (Token::simpleMatch(&tok, "try {"))
{
// Bail out all used variables
unsigned int indentlevel = 0;
for (const Token *tok2 = &tok; tok2; tok2 = tok2->next())
{
if (tok2->str() == "{")
++indentlevel;
else if (tok2->str() == "}")
{
if (indentlevel == 0)
break;
if (indentlevel == 1 && !Token::simpleMatch(tok2,"} catch ("))
return tok2;
--indentlevel;
}
else if (tok2->varId())
bailOutVar(checks,tok2->varId());
}
}
if (Token::Match(&tok, "%var% ("))
{
if (tok.str() == "sizeof")
return tok.next()->link();
// parse usage..
std::list<const Token *> var;
CheckNullPointer::parseFunctionCall(tok, var, 0);
for (std::list<const Token *>::const_iterator it = var.begin(); it != var.end(); ++it)
dereference(checks, *it);
}
else if (Token::simpleMatch(&tok, "( 0 &&"))
return tok.link();
if (tok.varId() != 0)
{
bool unknown = false;
if (Token::Match(tok.previous(), "[;{}=] %var% = 0 ;"))
setnull(checks, tok.varId());
else if (CheckNullPointer::isPointerDeRef(&tok, unknown))
dereference(checks, &tok);
else
// TODO: Report debug warning that it's unknown if a
// pointer is dereferenced
bailOutVar(checks, tok.varId());
}
else if (tok.str() == "delete")
{
const Token *ret = tok.next();
if (Token::simpleMatch(ret, "[ ]"))
ret = ret->tokAt(2);
if (Token::Match(ret, "%var% ;"))
return ret->next();
}
return &tok;
}
/** parse condition. @sa ExecutionPath::parseCondition */
bool parseCondition(const Token &tok, std::list<ExecutionPath *> &checks)
{
for (const Token *tok2 = &tok; tok2; tok2 = tok2->next())
{
if (tok2->str() == "(" || tok2->str() == ")")
break;
if (Token::Match(tok2, "[<>=] * %var%"))
dereference(checks, tok2->tokAt(2));
}
if (Token::Match(&tok, "!| %var% ("))
{
std::list<const Token *> var;
CheckNullPointer::parseFunctionCall(tok.str() == "!" ? *tok.next() : tok, var, 0);
for (std::list<const Token *>::const_iterator it = var.begin(); it != var.end(); ++it)
dereference(checks, *it);
}
return ExecutionPath::parseCondition(tok, checks);
}
void parseLoopBody(const Token *tok, std::list<ExecutionPath *> &checks) const
{
while (tok)
{
if (Token::Match(tok, "{|}|return|goto|break|if"))
return;
const Token *next = parse(*tok, checks);
if (next)
tok = tok->next();
}
}
};
/// @}
void CheckNullPointer::executionPaths()
{
// Check for null pointer errors..
Nullpointer c(this);
checkExecutionPaths(_tokenizer->tokens(), &c);
}
void CheckNullPointer::nullPointerError(const Token *tok)
{
reportError(tok, Severity::error, "nullPointer", "Null pointer dereference");
}
void CheckNullPointer::nullPointerError(const Token *tok, const std::string &varname)
{
reportError(tok, Severity::error, "nullPointer", "Possible null pointer dereference: " + varname);
}
void CheckNullPointer::nullPointerError(const Token *tok, const std::string &varname, const unsigned int line)
{
reportError(tok, Severity::error, "nullPointer", "Possible null pointer dereference: " + varname + " - otherwise it is redundant to check if " + varname + " is null at line " + MathLib::toString<unsigned int>(line));
}