V801. Decreased performance. It is better to redefine the N function argument as a reference. Consider replacing 'const T' with 'const .. &T' / 'const .. *T'.

The analyzer detected a construct that can be optimized. An object of type class or structure is passed to a function. This object is passed by value but is not modified because there is the key word const. Perhaps you should pass this object using a constant reference in the C++ language or a pointer in the C language.

For example:

bool IsA(const std::string s)
  return s == A;

When calling this function, the copy constructor will be called for the std::string class. If objects are often copied this way, this may significantly reduce the application's performance. You may easily optimize the code by adding the reference:

bool IsA(const std::string &s)
  return s == A;

The analyzer doesn't output the message if it is a plain old data (POD) structure whose size is not larger than that of the size of pointer. Passing such a structure by reference won't give any performance gain.


  • Wikipedia. Reference (C++).
  • Bjarne Stroustrup. The C++ Programming Language (Third Edition and Special Edition). 11.6 - Large Objects.

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