cppcheck should report enneficient std::strlen(str.c_str()) -> str.size()

[Dominique Pelle]

Consider the following c++ code:

#include <cstring>
#include <iostream>
#include <string>

int main()
{
  std::string s = "foo";

  // std::strlen(s.c_str(()) is inefficient and should rather
  // be written as s.size().
  std::cout << std::strlen(s.c_str()) << std::endl;
  return 0;
}

Neither gcc -Wall, nor clang -Wall, nor cppcheck warn about
the inneficient std::strlen(s.c_str()) which should rather
be s.size().

It may seem silly to write such inneficient code, but it can happen
by accident when refactoring code replacing C string with std::string.
It would be nice if cppcheck could warn about it.

[Daniel Marjamäki]

sounds good to me. I created https://trac.cppcheck.net/ticket/9015

If you want.. feel free to work on this.