[Possible false positive]

[Tobias Markus]

I found out that the code here:
https://coliru.stacked-crooked.com/view?id=4d0cc8073c899e6d

#include <bitset>
#include <iostream>

   // Not enum class since it must be used like a bitfield
  enum State
  {
    STATE_MAXIMIZED = 0,
    STATE_FULLSCREEN,
    STATE_RESIZING,
    STATE_ACTIVATED,
    STATE_COUNT
  };
  using StateBitset = std::bitset<STATE_COUNT>;

int main()
{
    StateBitset bitset;
    std::cout << "Bitset size: " << bitset.size() << '\n';
    std::cout << "size_t size: " << sizeof(size_t) << '\n';
}

void function(StateBitset bitset)
{
    std::cout << bitset.size() << '\n';
}

yields a potential false positive performance warning when running

% cppcheck --enable=performance ~/cppcheck_false_positive.cpp --check-level=exhaustive --force
Checking /Users/tobiasmarkus/cppcheck_false_positive.cpp ...
/Users/tobiasmarkus/cppcheck_false_positive.cpp:22:27: performance: Function parameter 'bitset' should be passed by const reference. [passedByValue]
void function(StateBitset bitset)
                          ^

The program's output is this:

g++ -std=c++23  -O2 -Wall -Wextra -pedantic -pthread -pedantic-errors main.cpp -lm  -latomic  && ./a.out

Bitset size: 4

size_t size: 8

which means that passing the bitset by value is actually equally expensive as passing it by reference.

[CHR]

Thanks for reporting, ticket is here: https://trac.cppcheck.net/ticket/12961