13.3 <cassert>

The <cassert> header (from the C standard <assert.h> header) declares the assert macro. The <cassert> header is unique in that you can #include it multiple times to obtain different effects (depending on whether the NDEBUG macro is defined at the time of #include <cassert>).

Assertions are checked at runtime. You can use templates to craft compile-time assertions. See Appendix B for information about the Boost project, which supports compile-time assertions.

Instead of assertions, consider using exceptions, which offer more flexibility and control.

assert macro Checks an assertion at runtime

void assert(int expression)


If enabled, the assert macro ensures the expression is true (nonzero). If so, nothing happens, and execution continues normally. If the expression evaluates to 0, assert prints a message to the standard error file and calls abort. The format of the message is implementation-defined, but it includes a textual representation of expression and the filename and line number where the assert call appears (that is, the values of the _ _FILE_ _ and _ _LINE_ _ macros).

If disabled, the assert macro does not evaluate expression and has no effect.

See Also

abort function in <cstdlib>, throw keyword

NDEBUG macro Enables or disables compilation of assertions

#define NDEBUG

#include <cassert>

The NDEBUG macro is not defined by <cassert> or anywhere else in the standard C++ library. Instead, you can define the macro before including the <cassert> header to disable the assert macro.

In one source file, you can define and undefine NDEBUG multiple times, each time followed by #include <cassert>, to enable or disable the assert macro multiple times in the same source file.

See Also

assert macro