In
programming, a gotcha is a valid construct in a system, program or
programming language
A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language.
The description of a programming ...
that works as documented but is
counter-intuitive
A paradox is a logically self-contradictory statement or a statement that runs contrary to one's expectation. It is a statement that, despite apparently valid reasoning from true premises, leads to a seemingly self-contradictory or a logically u ...
and almost invites mistakes because it is both easy to invoke and unexpected or unreasonable in its outcome.
[
]
Example
The classic gotcha in C/C++
C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
is the construct
if (a = b) code;
It is syntactically valid: it puts the value of b into a and then executes code if a is non-zero. Sometimes this is even intended. However most commonly it is a typo: the programmer probably meant
if (a b) code;
which executes code if a and b are equal.[Gotcha definition at The Jargon File]
/ref> Modern compiler
In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs tha ...
s will usually generate a warning when encountering the former construct (conditional branch on assignment, not comparison), depending on compiler options (e.g., the -Wall option for gcc). To avoid this gotcha, there is a recommendation"VOID EXP21-C. Place constants on the left of equality comparisons"
/ref> to keep the constants in the left side of the comparison, e.g. 42 x rather than x 42. This way, using = instead of
See also
* Usability
References
Further reading
*
External links
{{wiktionary, gotcha
C Traps and Pitfalls
by Andrew Koenig
C++ Gotchas
A programmer's guide to avoiding and correcting ninety-nine of the most common, destructive, and interesting C++ design and programming errors, by Stephen C. Dewhurst
Computer programming folklore
Programming language folklore
Programming language design