Line comments either start with a comment delimiter and continue until the end of the line, or in some cases, start at a specific column character line offset in the source code, and continue until the end of the line. Some programming languages employ both block and line comments with different comment delimiters. Other languages support only one type of comment. For example, Ada comments are line comments: they start with -- and continue to the end of the line. How best to make use of comments is subject to dispute; different commentators have offered varied and sometimes opposing viewpoints.
Comments can be used as a form of pseudocode to outline intention prior to writing the actual code. In this case it should explain the logic behind the code rather than the code itself. If this type of comment is left in, it simplifies the review process by allowing a direct comparison of the code with the intended results. A common logical fallacy is that code that is easy to understand does what it's supposed to do. Comments can be used to summarize code or to explain the programmer's intent. According to this school of thought, restating the code in plain English is considered superfluous; the need to re-explain code may be a sign that it is too complex and should be rewritten, or that the naming is bad.
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Comments may also be used to explain why a block of code does not seem to fit conventions or best practices. This is especially true of projects involving very little development time, or in bug fixing. For example:. Sometimes source code contains a novel or noteworthy solution to a specific problem. In such cases, comments may contain an explanation of the methodology. Such explanations may include diagrams and formal mathematical proofs.
This may constitute explanation of the code, rather than a clarification of its intent; but others tasked with maintaining the code base may find such explanation crucial. This might especially be true in the case of highly specialized problem domains; or rarely used optimizations, constructs or function-calls. For example, a programmer may add a comment to explain why an insertion sort was chosen instead of a quicksort , as the former is, in theory, slower than the latter.
This could be written as follows:. Logos , diagrams, and flowcharts consisting of ASCII art constructions can be inserted into source code formatted as a comment. Binary data may also be encoded in comments through a process known as binary-to-text encoding , although such practice is uncommon and typically relegated to external resource files.
Although a section marking the code appears as a comment, the diagram itself actually appears in an XML CDATA section, which is technically considered distinct from comments, but can serve similar purposes. Although this identical diagram could easily have been included as a comment, the example illustrates one instance where a programmer may opt not to use comments as a way of including resources in source code. In particular, many software maintainers put submission guidelines in comments to help people who read the source code of that program to send any improvements they make back to the maintainer.
Other metadata includes: the name of the creator of the original version of the program file and the date when the first version was created, the name of the current maintainer of the program, the names of other people who have edited the program file so far, the URL of documentation about how to use the program, the name of the software license for this program file, etc. When an algorithm in some section of the program is based on a description in a book or other reference, comments can be used to give the page number and title of the book or Request for Comments or other reference.
A common developer practice is to comment out a code snippet , meaning to add comment syntax causing that block of code to become a comment, so that it will not be executed in the final program. This may be done to exclude certain pieces of code from the final program, or more commonly it can be used to find the source of an error.
By systematically commenting out and running parts of the program, the source of an error can be determined, allowing it to be corrected. The above code fragment suggests that the programmer opted to disable the debugging option for some reason. Many IDEs allow quick adding or removing such comments with single menu options or key combinations. The programmer has only to mark the part of text they want to un comment and choose the appropriate option.
Programming tools sometimes store documentation and metadata in comments. Keeping documentation within source code comments is considered as one way to simplify the documentation process, as well as increase the chances that the documentation will be kept up to date with changes in the code. Forms of docstring are supported by Python , Lisp , Elixir , and Clojure.
NET assembly. Occasionally syntax elements that were originally intended to be comments are re-purposed to convey additional information to a program, such as " conditional comments ". Such "hot comments" may be the only practical solution that maintains backward-compatibility, but are widely regarded as a kludge.
There are cases where the normal comment characters are co-opted to create a special directive for an editor or interpreter. Somewhat similar is the use of comments in C to communicate to a compiler that a default "fallthough" in a case statement has been done deliberately:. Sometimes programmers will add comments as a way to relieve stress by commenting about development tools, competitors, employers, working conditions, or the quality of the code itself. There are various normative views and long-standing opinions regarding the proper use of comments in source code.
Experts have varying viewpoints on whether, and when, comments are appropriate in source code. In between these views is the assertion that comments are neither beneficial nor harmful by themselves, and what matters is that they are correct and kept in sync with the source code, and omitted if they are superfluous, excessive, difficult to maintain or otherwise unhelpful.
Comments are sometimes used to document contracts in the design by contract approach to programming. Depending on the intended audience of the code and other considerations, the level of detail and description may vary considerably. For example, the following Java comment would be suitable in an introductory text designed to teach beginning programming:. This level of detail, however, would not be appropriate in the context of production code, or other situations involving experienced developers.
Such rudimentary descriptions are inconsistent with the guideline: "Good comments There are many stylistic alternatives available when considering how comments should appear in source code.
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For larger projects involving a team of developers, comment styles are either agreed upon before a project starts, or evolve as a matter of convention or need as a project grows. Usually programmers prefer styles that are consistent, non-obstructive, easy to modify, and difficult to break.
The following code fragments in C demonstrate just a tiny example of how comments can vary stylistically, while still conveying the same basic information:.
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- Three ways to use MATLAB from R.
- Commenting out code.
Factors such as personal preference, flexibility of programming tools, and other considerations tend to influence the stylistic variants used in source code. For example, Variation Two might be disfavored among programmers who do not have source code editors that can automate the alignment and visual appearance of text in comments. Software consultant and technology commentator Allen Holub  is one expert who advocates aligning the left edges of comments: .
Line comments generally use an arbitrary delimiter or sequence of tokens to indicate the beginning of a comment, and a newline character to indicate the end of a comment. Often such a comment has to begin at far left and extend to the whole line. However in many languages, it is also possible to put a comment inline with a command line, to add a comment to it — as in this Perl example:.
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I mostly use matlab, but I would love to pass my data to R for the beautiful graphics engine. Hi Micha, thanks for your question! R outputForDebugging. You need to find where R is located on your computer, and cite that path. Also, when I try to run my matlab script using the system function, I get the error shown below. Regarding your errors, I am on a Mac and use the Terminal application to run stuff from the command line.
Hope that helps! Hi Victoria, he actually just posted it! Option 2 is about how to use R. She also […]. Three Ways to use Matlab from R 2. Thank you for this article. I am trying to run a script from Matlab,which itself call several functions, in R. Do you have any suggestions? I feel that the option 3 should definitely be preferred. As you wrote, it allows the user to easily run a full piece of Matlab code with loops and dependencies such as functions.
Moreover, the option 2 is far slower than the two others about times slower for the applications I made! Furthermore, with option 1, the results are shown in the Matlab console, and are not part of the R environment, contrary to option 3.
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Nevertheless, I encountered an unimportant error with the last line of option 3. Hello, and thanks for this great post. I have the following problem. I find getting data to and from matlab into R way too slow. For example, using R. Writing and reading temporary csv files for each loop iteration, needed in the other two methods, is way too slow too. Have you done better?
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You may be able to use a package like R. However, if you are passing data back and forth, it could definitely be too slow. Does it cope with non-trivial spm functions?
Thanks for the great post! An alternative might be to create a. Thanks for the great post.