variableScope false positive ?

[Sébastien Gallou]

Hello,

I'm using CppCheck 1.83, and I get the variableScope message on this piece
of code :

auto nbOccurences = 0;
auto isValid = false;
std::for_each(
    m_recentlySeenDevices.begin(),
    m_recentlySeenDevices.end(),
    [&](std::pair<boost::posix_time::ptime, std::string> value)
    {
       if (value.second == deviceName)
       {
          ++nbOccurences;
          if (nbOccurences >= m_minTimesPerPeriod)
             isValid = true;
       }
    });

The error occurs on "nbOccurences" variable, which I don't see how to
reduce scope without breaking the functionnal.

Is this a false positive ?

Thanks,

S. Gallou

[versat]

Can you please edit the post and add code formatting syntax, for example:

~~~
code goes here
~~~

Otherwise some characters can get wrongly interpreted which results in a wrong source code.

[Sébastien Gallou]

Yes, you're right.
Done.

[versat]

If i use exactly your source code i do not get a false positive with Cppcheck 1.83 or current development version.

If the code is inside a function then i do get the variableScope message:

void f()
{
    auto nbOccurences = 0;
    auto isValid = false;
    std::for_each(
        m_recentlySeenDevices.begin(),
        m_recentlySeenDevices.end(),
        [&](std::pair<boost::posix_time::ptime, std::string> value)
        {
            if (value.second == deviceName)
            {
                ++nbOccurences;
                if (nbOccurences >= m_minTimesPerPeriod)
                    isValid = true;
            }
        });
}

$ ./cppcheck --enable=all fp_variableScope.cpp
Checking fp_variableScope.cpp ...
[fp_variableScope.cpp:3]: (style) The scope of the variable 'nbOccurences' can be reduced.
[fp_variableScope.cpp:1]: (style) The function 'f' is never used.

[versat]

I tried to reduce the code so it does not use boost and does not error out via g++ -fsyntax-only.
For this code:

#include <vector>
#include <algorithm>

bool f(std::vector<int> vec, int someValue)
{
    auto nbOccurences = 0;
    auto isValid = false;
    std::for_each(
        vec.begin(),
        vec.end(),
        [&](int value)
        {
            if (value == someValue)
            {
                ++nbOccurences;
                if (nbOccurences >= 5)
                {
                    isValid = true;
                }
            }
        });
    return isValid;
}

Cppcheck reports the following:

$ g++ -fsyntax-only fp_variableScope.cpp

$ ./cppcheck --enable=all fp_variableScope.cpp
Checking fp_variableScope.cpp ...
[fp_variableScope.cpp:6]: (style) The scope of the variable 'nbOccurences' can be reduced.
[fp_variableScope.cpp:4]: (style) The function 'f' is never used.
(information) Cppcheck cannot find all the include files (use --check-config for details)

This really seems to be a false positive.

[versat]

I created the ticket 8541 for this issue.

[Sébastien Gallou]

Thanks a lot, I will follow it.