CodeQL documentation

Function declared in block

ID: cpp/function-in-block
Kind: problem
Security severity: 
Severity: recommendation
Precision: very-high
   - maintainability
   - readability
   - external/jsf
Query suites:
   - cpp-security-and-quality.qls

Click to see the query in the CodeQL repository

This rule finds functions that are declared in a block. It is confusing to declare a function at block scope, and the visibility of the function is not what would be expected. extern function declarations inside a block, which are allowed in C, are particularly confusing, as the scope of the declaration is the entire file, not just the block where it was declared.


Declare the function in file scope to prevent any confusion as to its visibility.


int f() {
	extern int other(); //scope of externs is the entire file, not just the 
	                    //block where it is declared

int g() {
	other(); //this will use the other() function declared inside f()


  • AV Rule 107, Joint Strike Fighter Air Vehicle C++ Coding Standards. Lockheed Martin Corporation, 2005.

  • MISRA C++ Rule 3-1-2, Guidelines for the use of the C++ language in critical systems. The Motor Industry Software Reliability Associate, 2008.

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