What Does Invalid Syntax Mean?
Computing applications and websites use code to implement the functionality they provide. Developers write this code in programming and markup languages, with a distinct set of rules for each language. As with natural languages, coding languages have their own grammar and vocabulary. If an excerpt of code contains errors, this code may be invalid. Invalid syntax can cause programs and sites to crash or function incorrectly.
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Code
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Programming and coding languages work in varied ways. In programming languages, such as Java for desktop programs or PHP for Web applications, the code specifies a series of instructions for the computer or Web server to execute. In markup languages, such as HTML and XML, documents list data items between tagged structures, defining the appearance and behavior of Web page content items and the structure of data sources. The syntax of a programming or markup language determines the structures that can appear within it, represented using text characters. For an application or site to function effectively, the syntax must be valid.
Errors
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Developers do not generally write perfect scripts on the first attempt. Many programming and markup languages use complex syntax structures, so mistakes are common. Typically, a project will undergo several stages of development, testing and debugging to identify and fix any issues arising from invalid syntax. The following sample code demonstrates a valid XML excerpt:
<face>
<eyes>Brown</eyes>
<mouth>Small</mouth>
</face>The following alternative code uses invalid syntax:
<face>
<eyes>Brown</eyes>
<mouth>Small<mouth>
</face>This code is invalid due to a simple typing error. The closing "mouth" tag is missing a forward slash character, which may cause the application using this code to fail.
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Effects
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The effects of invalid syntax range from minor to serious. In some cases, a program or Web page will continue to appear functional in spite of small errors. For example, Web browser programs can often render remaining code correctly in spite of some invalid syntax. However, a syntax error may cause an entire application to fail. The following sample Java code demonstrates a line using valid syntax:
String myWord = "person";The following amended version is invalid:
String myWord = "person;This code is invalid because the closing section of quotes defining the text string variable is missing. When Java processes this code, it will not only fail to handle this line correctly, but will process the following line incorrectly as well. This code will fail to compile, so the application will not be able to execute until the error has been fixed.
Solutions
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If you encounter invalid syntax errors as a user of a website or application, there is a limit to what you can do, as invalid syntax must be addressed by the developers responsible. If you are working on an application as a programmer, you must first locate the source of an error in order to fix it. For example, the following PHP code will generate an error:
$word_string = "Here are some words, with some inside "quotes" too";This code is invalid because PHP will interpret the quotes inside the text string variable as the end of the variable content. Depending on the Web server running the code, developers may see specific error messages when they attempt to view the page using the script in a browser, allowing them to find and then amend the invalid code.
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References
- Princeton University: Your First Java Program
- Hobart and William Smith Colleges; Introduction to Programming Using Java - Fundamental Building Blocks of Programs; David Eck; June 2011
- W3Schools: XML Elements
- W3Schools: XML Syntax Rules
- Oracle: The Java Tutorials - Strings
- PHP Manual: Strings
- PHP Manual: Runtime Configuration
Resources
- Photo Credit Photodisc/Photodisc/Getty Images
