MISRA C++:2008 Rule 3-2-4

An identifier with external linkage shall have exactly one definition

Description

This checker is deactivated in a default Polyspace^® as You Code analysis. See Checkers Deactivated in Polyspace as You Code Analysis (Polyspace Access).

Rule Definition

An identifier with external linkage shall have exactly one definition.¹

Rationale

If an identifier has multiple definitions or no definitions, it can lead to undefined behavior.

Polyspace Implementation

Polyspace

reports a variable if any of these conditions are true:

• You specify multiple definitions or tentative definitions of a symbol.

• There are undefined global variables in your code.

The checker is not raised on unused code such as

• Noninstantiated templates

• Uncalled static or extern functions

• Uncalled and undefined local functions

• Unused types and variables

Troubleshooting

If you expect a rule violation but Polyspace does not report it, see Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

Multiple Definitions of Identifier

This example uses two files:

• file1.cpp:

  
  typedef signed   int          int32_t;
  
  namespace NS {
  	extern int32_t a; //Noncompliant
  
  	void foo(){
  		a = 0;
  		
  	}
  }; 

• file2.cpp:

  
  typedef signed   int          int32_t;
  typedef signed   long long         int64_t;
  
  namespace NS {
  	extern int64_t a; //Noncompliant
  	void bar(){
  		++a;
  		
  	}
  };

The same identifier a is defined in both files.

Check Information

Group: Basic Concepts

Category: Required

Version History

Introduced in R2013b