Gotcha (programming)


In programming, a gotcha is a valid construct in a system, program or programming language that works as documented but is counter-intuitive 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++ is the construct

if 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 code;

which executes code if a and b are equal. Modern compilers will usually generate a warning when encountering the former construct, depending on compiler options. To avoid this gotcha, there is a recommendation to keep the constants in the left side of the comparison, e.g. 42 x rather than x 42. This way, using = instead of will cause a compiler error. Many kinds of gotchas are not detected by compilers, however.