A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
Programming style is a set of rules or guidelines used when writing the source code for a computer program. It is often claimed that following a particular programming style will help programmers to read and understand source code conforming to the style, and help to avoid introducing errors.A...
, practices and methods for each aspect of a piece program written in this language. These conventions usually cover file organization, indentation
Indentation
An indentation may refer to:* A notch, or deep recesses; for instance in a coastline, or a carving in rock* The placement of text farther to the right to separate it from surrounding text....
In computer programming, a comment is a programming language construct used to embed programmer-readable annotations in the source code of a computer program. Those annotations are potentially significant to programmers but typically ignorable to compilers and interpreters. Comments are usually...
In programming languages, a declaration specifies the identifier, type, and other aspects of language elements such as variables and functions. It is used to announce the existence of the element to the compiler; this is important in many strongly-typed languages that require variables and their...
In computer programming a statement can be thought of as the smallest standalone element of an imperative programming language. A program written in such a language is formed by a sequence of one or more statements. A statement will have internal components .Many languages In computer programming...
Whitespace is an esoteric programming language developed by Edwin Brady and Chris Morris at the University of Durham . It was released on 1 April 2003 . Its name is a reference to whitespace characters...
Best coding practices for software development can be broken into many levels based on the coding language, the platform, the target environment and so forth...
A programmer, computer programmer or coder is someone who writes computer software. The term computer programmer can refer to a specialist in one area of computer programming or to a generalist who writes code for many kinds of software. One who practices or professes a formal approach to...
are highly recommended to follow these guidelines to help improve the readability
Readability
Readability is the ease in which text can be read and understood. Various factors to measure readability have been used, such as "speed of perception," "perceptibility at a distance," "perceptibility in peripheral vision," "visibility," "the reflex blink technique," "rate of work" , "eye...
In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...
Software Maintenance in software engineering is the modification of a software product after delivery to correct faults, to improve performance or other attributes....
easier. Coding conventions are only applicable to the human maintainers and peer review
Peer review
Peer review is a process of self-regulation by a profession or a process of evaluation involving qualified individuals within the relevant field. Peer review methods are employed to maintain standards, improve performance and provide credibility...
ers of a software project. Conventions may be formalized in a documented set of rules that an entire team or company follows, or may be as informal as the habitual coding practices of an individual. Coding conventions are not enforced by compiler
Compiler
A compiler is a computer program that transforms source code written in a programming language into another computer language...
s. As a result, not following some or all of the rules has no impact on the executable programs created from the source code.
Software Maintenance in software engineering is the modification of a software product after delivery to correct faults, to improve performance or other attributes....
is the most often cited reason for following coding conventions. In their introduction to code conventions for the Java Programming Language, Sun Microsystems provides the following rationale:
Code conventions are important to programmers for a number of reasons:
80% of the lifetime cost of a piece of software goes to maintenance.
Hardly any software is maintained for its whole life by the original author.
Code conventions improve the readability of the software, allowing engineers to understand new code more quickly and thoroughly.
If you ship your source code as a product, you need to make sure it is as well packaged and clean as any other product you create.
In software development, peer review is a type of software review in which a work product is examined by its author and one or more colleagues, in order to evaluate its technical content and quality.-Purpose:...
frequently involves reading source code. This type of peer review is primarily a defect
Software bug
A software bug is the common term used to describe an error, flaw, mistake, failure, or fault in a computer program or system that produces an incorrect or unexpected result, or causes it to behave in unintended ways. Most bugs arise from mistakes and errors made by people in either a program's...
detection activity. By definition, only the original author of a piece of code has read the source file before the code is submitted for review. Code that is written using consistent guidelines is easier for other reviewers to understand and assimilate, improving the efficacy of the defect detection process.
Even for the original author, consistently coded software eases maintainability. There is no guarantee that an individual will remember the precise rationale for why a particular piece of code was written in a certain way long after the code was originally written. Coding conventions can help. Consistent use of whitespace
Whitespace (computer science)
In computer science, whitespace is any single character or series of characters that represents horizontal or vertical space in typography. When rendered, a whitespace character does not correspond to a visual mark, but typically does occupy an area on a page...
improves readability and reduces the time it takes to understand the software.
Code refactoring is "disciplined technique for restructuring an existing body of code, altering its internal structure without changing its external behavior", undertaken in order to improve some of the nonfunctional attributes of the software....
refers to a software maintenance activity where source code
Source code
In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...
is modified to improve readability or improve its structure. Software is often refactored to bring it into conformance with a team's stated coding standards after its initial release. Any change that does not alter the behavior of the software can be considered refactoring. Common refactoring activities are changing variable names, renaming methods
Rename method
Rename Method is a refactoring that changes a name of a method into a new one, that better reveals its purpose.To have clearer, more understandable code, programmers would optimally want to change method names to reflect exactly what the method does...
, moving methods or whole classes and breaking large methods (or functions) into smaller ones.
Agile software development is a group of software development methodologies based on iterative and incremental development, where requirements and solutions evolve through collaboration between self-organizing, cross-functional teams...
plan for regular (or even continuous) refactoring making it an integral part of the team software development process
Software development process
A software development process, also known as a software development life cycle , is a structure imposed on the development of a software product. Similar terms include software life cycle and software process. It is often considered a subset of systems development life cycle...
.
Task automation
Coding conventions allow to have simple scripts or programs whose job is to process source code for some purpose other than compiling it into an executable. It is common practice to count the software size (Source lines of code
Source lines of code
Source lines of code is a software metric used to measure the size of a software program by counting the number of lines in the text of the program's source code...
) to track current project progress or establish a baseline for future project estimates
Estimation in software engineering
The ability to accurately estimate the time and/or cost taken for a project to come in to its successful conclusion is a serious problem for software engineers. The use of a repeatable, clearly defined and well understood software development process has, in recent years, shown itself to be the...
.
Consistent coding standards can, in turn, make the measurements more consistent. Special tag
Tag (metadata)
In online computer systems terminology, a tag is a non-hierarchical keyword or term assigned to a piece of information . This kind of metadata helps describe an item and allows it to be found again by browsing or searching...
s within source code comments are often used to process documentation, two notable examples are javadoc
Javadoc
Javadoc is a documentation generator from Sun Microsystems for generating API documentation in HTML format from Java source code.The "doc comments" format used by Javadoc is the de facto industry standard for documenting Java classes. Some IDEs, such as Netbeans and Eclipse automatically generate...
Doxygen is a documentation generator for multiple programming languages.Doxygen is a tool for writing software reference documentation. The documentation is written within code, and is thus relatively easy to keep up to date...
. The tools specifies the use of a set of tags, but their use within a project is determined by convention.
Coding conventions simplify writing new software whose job is to process existing software. Use of static code analysis
Static code analysis
Static program analysis is the analysis of computer software that is performed without actually executing programs built from that software In most cases the analysis is performed on some version of the source code and in the other cases some form of the object code...
has grown consistently since the 1950s. Some of the growth of this class of development tools stems from increased maturity and sophistication of the practitioners themselves (and the modern focus on safety and security
Vulnerability (computing)
In computer security, a vulnerability is a weakness which allows an attacker to reduce a system's information assurance.Vulnerability is the intersection of three elements: a system susceptibility or flaw, attacker access to the flaw, and attacker capability to exploit the flaw...
), but also from the nature of the languages themselves.
Language factors
All software practitioners must grapple with the problems of organizing and managing very many detailed instructions, each of which will eventually be processed in order to perform the task for which it was written. For all but the smallest software projects, source code (instructions) are partitioned into separate files
Computer file
A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished...
and frequently among many directories. It was natural for programmers to collect closely related functions (behaviors) in the same file and to collect related files into directories. As software development evolved from purely procedural programming
Procedural programming
Procedural programming can sometimes be used as a synonym for imperative programming , but can also refer to a programming paradigm, derived from structured programming, based upon the concept of the procedure call...
Object-oriented programming is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction,...
C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
), it became the practice to write the code for a single (public) class in a single file (the 'one class per file' convention).
Java has gone one step further - the Java compiler returns an error if it finds more than one public class per file.
A convention in one language may be a requirement in another. Language conventions also affect individual source files. Each compiler (or interpreter) used to process source code is unique. The rules a compiler applies to the source creates implicit standards. For example, Python code is much more consistently indented than, say Perl, because whitespace (indentation) is actually significant to the interpreter. Python does not use the brace syntax Perl uses to delimit functions. Changes in indentation serve as the delimiters. Tcl, which uses a brace syntax similar to Perl or C/C++ to delimit functions, does not allow the following, which seems fairly reasonable to a C programmer:
set i 0
while {$i < 10}
{
puts "$i squared = [expr $i*$i]"
incr i
}
The reason is that in Tcl, curly braces are not used only to delimit functions as in C or Java. More
generally, curly braces are used to group words together into a single argument.
In Tcl, the wordwhile takes two arguments, a condition and an action. In the example above, while is missing its second argument, its action (because the Tcl also uses the newline character to delimit the end of a command).
Common conventions
As mentioned above, common coding conventions may cover the following areas:
In computer programming, a comment is a programming language construct used to embed programmer-readable annotations in the source code of a computer program. Those annotations are potentially significant to programmers but typically ignorable to compilers and interpreters. Comments are usually...
In computer programming, an indent style is a convention governing the indentation of blocks of code to convey the program's structure. This article largely addresses the C programming language and its descendants, but can be applied to most other programming languages...
Best coding practices for software development can be broken into many levels based on the coding language, the platform, the target environment and so forth...
Programming style is a set of rules or guidelines used when writing the source code for a computer program. It is often claimed that following a particular programming style will help programmers to read and understand source code conforming to the style, and help to avoid introducing errors.A...
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
this would involve having statements written like this:
++a;
b = a;
But not like this:
++a; b = a;
Boolean values in decision structures
Some programmers suggest that coding where the result of a decision is merely the computation of a Boolean
Boolean datatype
In computer science, the Boolean or logical data type is a data type, having two values , intended to represent the truth values of logic and Boolean algebra...
value, are overly verbose and error prone. They prefer to have the decision in the computation itself, like this:
Object code, or sometimes object module, is what a computer compiler produces. In a general sense object code is a sequence of statements in a computer language, usually a machine code language....
for both forms. However, stylistically, programmers disagree which form is easier to read and maintain.
Arguments in favor of the longer form include: it is then possible to set a per-line breakpoint on one branch of the decision; further lines of code could be added to one branch without refactoring
Refactoring
Code refactoring is "disciplined technique for restructuring an existing body of code, altering its internal structure without changing its external behavior", undertaken in order to improve some of the nonfunctional attributes of the software....
the return line, which would increase the chances of bugs being introduced; the longer form would always permit a debugger to step to a line where the variables involved are still in scope.
Left-hand comparisons
In languages which use one symbol (typically a single equals sign, (=)) for assignment
Assignment (computer science)
In computer programming, an assignment statement sets or re-sets the value stored in the storage location denoted by a variable name. In most imperative computer programming languages, assignment statements are one of the basic statements...
and another (typically two equals signs, () for comparison
Relational operator
In computer science, a relational operator is a programming language construct or operator that tests or defines some kind of relation between two entities. These include numerical equality and inequalities...
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
PHP is a general-purpose server-side scripting language originally designed for web development to produce dynamic web pages. For this purpose, PHP code is embedded into the HTML source document and interpreted by a web server with a PHP processor module, which generates the web page document...
Perl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular...
numeric context, and most languages in the last 15 years), and where assignments may be made within control structures, there is an advantage to adopting the left-hand comparison style: to place constants or expressions to the left in any comparison.
Here are both left and right-hand comparison styles, applied to a line of Perl
Perl
Perl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular...
code. In both cases, this compares the value in the variable $a against 42, and if it matches, executes the code in the subsequent block.
if ($a 42) { ... } # A right-hand comparison checking if $a equals 42.
if (42
$a) { ... } # Recast, using the left-hand comparison style.
The difference occurs when a developer accidentally types = instead of :
if ($a = 42) { ... } # Inadvertent assignment which is often hard to debug
if (42 = $a) { ... } # Compile time error indicates source of problem
The first (right-hand) line now contains a potentially subtle flaw: rather than the previous behaviour, it now sets the value of $a to be 42, and then always runs the code in the following block. As this is syntactically legitimate, the error may go unnoticed by the programmer, and the software may ship with a bug.
The second (left-hand) line contains a semantic error, as numeric values cannot be assigned to. This will result in a diagnostic message being generated when the code is compiled, so the error cannot go unnoticed by the programmer.
Some languages have built-in protections against inadvertent assignment. Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
and C#, for example, do not support automatic conversion to boolean for just this reason.
The use of logical control structures for looping adds to good programming style as well. It helps someone reading code to better understand the program's sequence of execution (in imperative programming
Imperative programming
In computer science, imperative programming is a programming paradigm that describes computation in terms of statements that change a program state...
languages). For example, in pseudocode:
i = 0 while i < 5 print i * 2
i = i + 1 end while print "Ended loop"
The above snippet obeys the naming and indentation style guidelines, but the following use of the "for" construct may be considered easier to read:
for i = 0, i < 5, i=i+1 print i * 2 print "Ended loop"
In many languages, the often used "for each element in a range" pattern can be shortened to:
for i = 0 to 5 print i * 2 print "Ended loop"
In programming languages that allow curly brackets, it has become common for style documents to require that even where optional, curly brackets be used with all control flow
Control flow
In computer science, control flow refers to the order in which the individual statements, instructions, or function calls of an imperative or a declarative program are executed or evaluated....
constructs.
for (i = 0 to 5) { print i * 2;
} print "Ended loop";
This prevents program-flow bugs which can be time-consuming to track down, such as where a terminating semicolon is introduced at the end of the construct (a common typo):
for (i = 0; i < 5; ++i);
printf("%d\n", i*2); /* The incorrect indentation hides the fact
that this line is not part of the loop body. */
printf("Ended loop");
...or where another line is added before the first:
for (i = 0; i < 5; ++i)
fprintf(logfile, "loop reached %d\n", i);
printf("%d\n", i*2); /* The incorrect indentation hides the fact
that this line is not part of the loop body. */
printf("Ended loop");
Lists
Where items in a list are placed on separate lines, it is sometimes considered good practice to add the item-separator after the final item, as well as between each item, at least in those languages where doing so is supported by the syntax (e.g., C, Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
)
const char *array[] = {
"item1",
"item2",
"item3", /* still has the comma after it */
};
This prevents syntax errors or subtle string-concatenation bugs when the list items are re-ordered or more items are added to the end, without the programmer's noticing the "missing" separator on the line which was previously last in the list. However, this technique can result in a syntax error (or misleading semantics) in some languages. Even for languages that do support trailing commas, not all list-like syntactical constructs in those languages may support it.
In computer programming, an indent style is a convention governing the indentation of blocks of code to convey the program's structure. This article largely addresses the C programming language and its descendants, but can be applied to most other programming languages...
MISRA C is a software development standard for the C programming language developed by MISRA . Its aims are to facilitate code safety, portability and reliability in the context of embedded systems, specifically those systems programmed in ISO C...
Programming style is a set of rules or guidelines used when writing the source code for a computer program. It is often claimed that following a particular programming style will help programmers to read and understand source code conforming to the style, and help to avoid introducing errors.A...
The GNU Coding Standards are a set of rules and guidelines for writing programs that work consistently within the GNU system. The GNU Coding Standards were written by Richard Stallman and other GNU Project volunteers. The standards document is part of the GNU Project and is available from the GNU...
[ftp://ftp.netbsd.org/pub/NetBSD/NetBSD-current/src/share/misc/style The NetBSD source code style guide] (formerly known as the BSD Kernel Normal Form) (PDF)
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