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10.6 | Analyzing source code | Languages | C/C++/Objective-C | Understanding the analysis

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Understanding the analysis

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Analysis scope

This page outlines the general analysis scope. The CFamily analysis scope is a subset of the general scope defined by file extensions specified using the following SonarScanner properties: sonar.c.file.suffixes, sonar.cpp.file.suffixes, and sonar.objc.file.suffixes.

The files that are ultimately analyzed depend on the selected analysis mode:

  • In AutoConfig mode, every non-header source file within the CFamily analysis scope is analyzed individually. That's why the sonar.sources property should be set to prevent the analysis of third-party code.
  • In Compilation Database mode, the analyzed files represent the intersection between the CFamily analysis scope and the `file` entry in the compile_commands.json. This implies that only compiled files within the CFamily scope are analyzed. Therefore, ensuring that the compile_commands.json accurately encompasses the entire project is advisable.
  • In both modes, header files get analyzed in the context of the source files in which they are included. This means header files not included in any source file will not be analyzed.

Measures for header files

Each time a header file is analyzed as part of a compilation unit, the measures are computed for this header: statements, functions, classes, cyclomatic complexity, and cognitive complexity. Each measure may be computed more than once for a given header. In that case, the largest value is stored for each measure.

Language-specific rule tags

On top of the built-in rule tags, a few additional rule tags are specific to C/C++/Objective-C rules.

C++ standard version-related rule tags

Some rules are relevant only since a specific version of the C++ standard. These rules will run only when analyzing a C++ code compiled against a later or equal standard version. The following tags are used to mark these rules for the corresponding C++ standard version:

  • since-c++11 
  • since-c++14
  • since-c++17
  • since-c++20

C++ rules not carrying any of these four tags started running since C++98. 

Implementation-related rule tags

  • full-project: This tag is for rules that do cross-compilation unit analysis. For these rules to work properly, it is important to analyze the entire project. Excluding part of the project from the analysis will impact the accuracy of these rules: it might lead to false positives or negatives.
  • symbolic-execution: this tag is for rules that reason about the program's state. They usually work together to find path-sensitive bugs and vulnerabilities. Once a fatal state of the program is reached, one issue will be raised, and the symbolic execution analysis of the current path will stop. For that reason, evaluating these rules independently of each other is not recommended as it might give a false sense of undetected issues. It is important to keep in mind that Sonar is always working on improving these rules, as symbolic execution can never be perfect.

External standard rule tags

The following tags indicate how a rule relates to the MISRA guidelines:

  • based-on-misra: This tag is for rules that address the same issues as MISRA rules but only partially correspond to what MISRA specifies (usually to make them less strict).
  • misra-c++2008
  • misra-c++2023
  • misra-c2004
  • misra-c2012

The following tags represent the category of the rule according to the MISRA compliance 2020 document and indicate whether violations of the rule are permitted (see Chapter 5: “The guideline re-categorization plan”):

  • misra-mandatory
  • misra-required
  • misra-advisory

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