Our website uses cookies to enhance your browsing experience.
Accept
to the top
close form

Fill out the form in 2 simple steps below:

Your contact information:

Step 1
Congratulations! This is your promo code!

Desired license type:

Step 2
Team license
Enterprise license
** By clicking this button you agree to our Privacy Policy statement
close form
Request our prices
New License
License Renewal
--Select currency--
USD
EUR
* By clicking this button you agree to our Privacy Policy statement

close form
Free PVS‑Studio license for Microsoft MVP specialists
* By clicking this button you agree to our Privacy Policy statement

close form
To get the licence for your open-source project, please fill out this form
* By clicking this button you agree to our Privacy Policy statement

close form
I am interested to try it on the platforms:
* By clicking this button you agree to our Privacy Policy statement

close form
check circle
Message submitted.

Your message has been sent. We will email you at


If you do not see the email in your inbox, please check if it is filtered to one of the following folders:

  • Promotion
  • Updates
  • Spam

Webinar: Parsing C++ - 10.10

>
>
>
V1068. Do not define an unnamed namespa…
menu mobile close menu
Analyzer diagnostics
General Analysis (C++)
General Analysis (C#)
General Analysis (Java)
Micro-Optimizations (C++)
Diagnosis of 64-bit errors (Viva64, C++)
Customer specific requests (C++)
MISRA errors
AUTOSAR errors
OWASP errors (C#)
Problems related to code analyzer
Additional information
toggle menu Contents

V1068. Do not define an unnamed namespace in a header file.

Jan 13 2021

The analyzer detected an anonymous namespace declared in the header file. Such a header file creates copies of symbols with internal linkage in each translation unit that includes this header file. This leads to object files bloat, which may be unwanted behavior.

Consider a simple example of a header file with an anonymous namespace:

// utils.hpp
#pragma once
#include <iostream>

namespace
{
  int global_variable;
  void set_global_variable(int v)
  {
    std::cout << global_variable << std::endl;
    global_variable = v;
  }
}

When the 'utils.hpp' header file is included, each translation unit will receive its own instance of the 'global_variable' variable. The variable will not relate to other instances and will not be accessible from other translation units. Several redundant 'set_global_variable' functions will also be generated. Before the C++17 standard, such code could occur in header-only libraries in order not to violate the One Definition Rule when including header files in multiple translation units. Also, such code may appear due to careless refactoring, for example, when moving an anonymous namespace from a compiled file to a header file.

it is worth mentioning that this rule also applies to unnamed namespaces nested in other namespaces:

namespace my_namespace
{
  int variable1; // namespace-scope non-const variable
                 // 'variable1' has external linkage

  namespace // <=
  {
    int variable2; // unnamed namespace applies 'static'
                   // 'variable2' has internal linkage
  }
}

If you need to create exactly one instance of a symbol for the header-only library, you can use the 'inline' specifier. Starting with C++17, it applies to variables as well:

// utils.hpp
#pragma once
#include <iostream>

inline int global_variable; // ok since C++17

inline void set_global_variable(int v)
{
  std::cout << global_variable << std::endl;
  global_variable = v;
}

If an earlier version of the standard is used, but the library is not header-only, then you can declare the symbols as 'extern' in the header file and define them in one of the translation units:

// utils.hpp
#pragma once

extern int global_variable;
void set_global_variable(int v); // functions implicitly 
                                 // have external linkage ('extern')

// utils.cpp
#include "utils.hpp"
#include <iostream>

int global_variable;

void set_global_variable(int v)
{
  std::cout << global_variable << std::endl;
  global_variable = v;
}

In the case when an older version of the standard is used, but the library must be header-only, the warning can be suppressed with a comment:

// utils.hpp
#pragma once
#include <iostream>

namespace //-V1068
{
  int global_variable;
  void set_global_variable(int v)
  {
    std::cout << global_variable << std::endl;
    global_variable = v;
  }
}

This diagnostic is classified as:

  • CERT-DCL59-CPP

You can look at examples of errors detected by the V1068 diagnostic.