3. Guidance

NASA programs and projects have multi-year life cycle times. Often the software personnel who develop the original software work products move on to other projects. These developers are then backfilled on the team by other developers for the remainder of the development, operations, maintenance, and disposal phases of the life cycle. This personnel turnover process may occur several times during the project's life cycle. The use of uniform software coding methods, standards, and/or criteria ensures uniform coding practices, reduces errors through safe language subsets, and improves code readability. Verification that these practices have been adhered to reduces the risk of software malfunction for the project during its operations and maintenance phases.

There are five key benefits of using coding standards:

1. Understanding, maintainability, and readability of the code.

2. Consistent code quality — no matter who writes the code.

3. Software security from the start.

4. Reduced development costs.

5. Testability of the code.

3. Guidance

Coding standards for software have been developed for years and represent lessons learned by coding experts.  Coding standards help prevent or reduce unsafe coding practices such as defect-prone coding styles, security issues from specific coding sequences, and numerous coding errors, mistakes, and misunderstandings. 

"Coding standards are the ‘materials and manufacturing standards’ for implemented software...
Human-rated certification and mission-critical software both require applying a recognized coding standard, one that is supported by automated analysis tools, for all software required to be certified for human spaceflight and mission-critical applications.  Manual verification is all but impossible.

The reduction in effort by simply adhering to a coding standard that can be tested through automation is the one certification process that truly has no other efficient verification method. ...  As security becomes an issue, security coding standards should also be applied.” 

3.1 General Coding Standard Guidance

Planning for the adoption and use of coding standards at the beginning of a software development activity sets the right tone and approach for the development team.

Software coding standards are classified by language, usage, and severity levels. Language-specific rules and best coding practices are usually determined by experts in the particular language [e.g., C++, ADA] and tailored as needed by the project. The user sets usage types and severity levels.

"A comprehensive coding standard encompasses all aspects of code construction. ...Properly completed source code reflects a harmonized style as if a single developer wrote the code in one session. At the inception of a software project, a coding standard is established to ensure that all developers are working in concert. When the software project incorporates existing source code or performs maintenance on an existing software system, the coding standard states how to deal with the existing codebase.
"The readability of source code has a direct impact on how well a developer comprehends a software system. Code maintainability refers to how easily that software system can be changed to add new features, modify existing features, fix bugs, or improve performance. Although readability and maintainability are the results of many factors, one particular facet of software development upon which all developers influence is the coding technique. One of the easiest methods to ensure a team of developers will yield quality code is to establish a coding standard, which is then enforced at routine code reviews"

Over time, correlations between bugs and coding practices resulted in rules that helped prevent coding errors from occurring.

In a team environment or group collaboration, the use of coding standards ensures uniform coding practices and reduces oversight errors and the time spent in code reviews. When NASA software development work is outsourced to a supplier (see Topic 7.3 - Acquisition Guidance), having a set of coding standards in place helps ensure that the contractor's code meets quality requirements mandated by NASA in the NASA Software Assurance Standard, NASA STD 8739.8.

A coding standard document may be written as a general document that is independent of any project. Project-specific needs are then added as amendments to the document. Note that there is an important difference between a coding style and a coding standard. A coding style specifies how you indent lines or employ tabs and spaces to make the code easier to read by the software development team. A coding standard, which often includes a coding style, goes beyond just how to name a variable. It tells you how that variable is to be treated and when it is to be used (and not used).

Correlations between bugs and coding practices resulted in rules that helped prevent coding errors from occurring. These activities resulted in recommendations to develop and use coding standards.

In a team environment or group collaboration, the use of coding standards ensures uniform coding practices and reduces oversight errors and the time spent in code reviews. When NASA software development work is outsourced to a supplier (see Topic 7.3 - Acquisition Guidance), having a set of coding standards in place helps ensure that the code meets quality requirements mandated by NASA in the NASA Software Assurance Standard, NASA STD 8739.8.

A coding standard document may be written as a general document that is independent of any project. Project-specific needs are then added as amendments to the document. Note that there is an important One way to tell the difference between a coding style and a coding standard is to assess the functionality of code changed due to applying the coding style or standard. If the coding style was not followed, the code should still work the same way, with the same behavior and safety checks. However, if the coding standard is not correctly applied, the code's "safety" and/or functionality have likely changed. A coding standard is more important than a coding style since the standard affects the code's behavior.. A coding style specifies how you indent lines or employ tabs and spaces to make the code easier to read by the software development team. A coding standard, which often includes a coding style, goes beyond just how to name a variable. It tells you how that variable is to be treated and when it is to be used (and not used). 

3.2 How Coding Standards are Classified

Software coding standards are classified by language, usage, and severity levels. Industry experts determine Language-specific rules and best coding practices in that particular language. The user sets usage types and severity levels.