latest cppcheck commits: new FPs for "constant" conditions in loops

[Martin]

Hi,

recently (f.e. as a result of the main branch commits of the last few days) a lot of false-positives showed up like this one:

      for (size_t i = bodyStartIdx; i < m_TextChunks.size(); ++i)
      {
         if (i != bodyStartIdx)
         {
            bodyText += "\n";
         }
         bodyText += m_TextChunks[i];
      }

(style) Condition 'i!=bodyStartIdx' is always true
This is only true for the first iteration.

I've seen findings like this also for other kind of loops.

Could you please check?

Thanks,
Martin

[Martin]

Second example:

         for (auto sectIdx = linkSectionIdx; sectIdx < getVector().size(); ++sectIdx)
         {
            if (sectIdx == linkSectionIdx)
            {
               result += 1;
            }
            else
            {
               result += 2;
            }
         }

--> (style) Condition 'sectIdx==linkSectionIdx' is always false

Maybe there should be a bailout for conditions where variables are involved which may be changed in each iteration of a loop?

[CHR]

I have seen similar FPs recently, but at least your examples seem to be fixed in head. Have you tried https://github.com/danmar/cppcheck/commit/c630be7f8f318194d7a1cb4dae274ee38bf785d9 or newer?

[Martin]

Yes, with that commit I got the FPs mentioned above. Maybe I missed to copy some parts of the file that trigger these FPs in the analysis, I'll look into that later.

Btw, I can't build the current head; for 7a6d7f7c2 I get:

lib/valueflow.cpp:2609:1: error: expected initializer before ‘Analyzer’
Analyzer::Result result{};
^~~~~~~~
lib/valueflow.cpp:2610:1: error: expected unqualified-id before ‘for’
for (const ValueFlow::Value& v : values)
^~~
lib/valueflow.cpp:2614:1: error: expected unqualified-id before ‘return’
return result;
^~~~~~
lib/valueflow.cpp:2615:1: error: expected declaration before ‘}’ token
}
^

[Martin]

I retried, with the latest commit I get the FP for a file containing only this code:

   void foo()
   {
      auto iterBegin = container.begin();
      for (auto iter = iterBegin; iter != iterEnd; ++iter)
      {
         if(iter != iterBegin)
         {
            result << delimiter;
         }
      }
   }

./cppcheck --enable=all /home/user/Desktop/21-08-03.cpp
Checking /home/user/Desktop/21-08-03.cpp ...
/home/user/Desktop/21-08-03.cpp:6:18: style: Condition 'iter!=iterBegin' is always true [knownConditionTrueFalse]
if(iter != iterBegin)
^
/home/user/Desktop/21-08-03.cpp:4:22: note: iter is assigned 'iterBegin' here.
for (auto iter = iterBegin; iter != iterEnd; ++iter)
^
/home/user/Desktop/21-08-03.cpp:4:54: note: iter is incremented', new value is symbolic=iterBegin+1
for (auto iter = iterBegin; iter != iterEnd; ++iter)
^
/home/user/Desktop/21-08-03.cpp:6:18: note: Condition 'iter!=iterBegin' is always true
if(iter != iterBegin)
^
/home/user/Desktop/21-08-03.cpp:1:0: style: The function 'foo' is never used. [unusedFunction]

^

[CHR]

Thanks for the example, ticket is here: https://trac.cppcheck.net/ticket/10395