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Programming Pitfalls

Top Ten Mistakes a Programmer Can Make

Jessica Thornsby

Julian Bucknall has written down the big ten mistakes he expects every programmer to make.

Having a tough week at work? Chance are you’re not alone, as Julian Bucknall has posted the top ten mistakes every programmer makes. Take a look, and see if any of these pain-points sound familiar:

Code written for a compiler, not for a person. It doesn’t make any difference to the compiler if you use more human-readable identifiers, and chances are the extra time required for the compiler to translate longer identifiers, is insignificant. So, why not write code that a human being can read and understand? It’s also worth remembering that not every programmer who comes into contact with your code will know the precedence of operators, so retaining needless – but useful – parentheses could save them a lot of head-scratching.

Big routines. Long methods are typically difficult to understand, maintain and test, as testing is a function of the number of possible paths through a method.

Destructive optimism. This is the root of all evil, according to scientist Donald Knuth. Write your code, profile it and pinpoint the real bottlenecks, rather than overcomplicating things by trying to solve problems that haven’t even occurred yet.

Global variables. These are visible everywhere, which means the developer has no control over how they’re changed and accessed, and for Bucknall, therein lies the problem. A global value may have a certain value before a call to a routine, and a different one after you get control back. He reports the same problem with singletons: their persistence makes them difficult to test.

Not making estimates. Taking into consideration factors such as the number of simultaneous users, records and response times, can make or break an application.

Off by one. Writing a loop with an index so that the index is incremented either once too often or once too little, resulting in a loop being traversed an incorrect number of times. This can also cause a non-existent element of the array to be accessed or written to, or an element to be missed altogether.

Suppressed exceptions. Bucknall believes that exceptions can make for robust software, but programmers sometimes make the mistake of being vague about the type of exception they wish to catch, or catch all the exceptions and then ignore them.

Storing passwords in plain text.

Un-validated user input. Apps can now be used by countless users simultaneously, thanks to the World Wide Web, and there are no shortage of attacks that take advantage of this, meaning it’s crucial to check user input. If an app does not validate user input, SQL or HTML fragments could result in some hacked SQ1 executing, or hacked HTML/JavaScript being produced. “Always assume the user is a hacker trying to crash or take over your application and validate or sanitise user input,” he advises.

But, what’s the biggest mistake a programmer can make? Not being up to date. Bucknall advises keeping on top of all the latest techniques, technologies and trends, to make your day-to-day development as pain free as possible.


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