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Chapter 5: Assertion

Introduction

An assertion is a predicate that the presented condition must be true at the moment the assertion
is encountered by the software. Most common are simple assertions, which are validated at
execution time. However, static assertions are checked at compile time.

Syntax

• assert(expression)
• static_assert(expression, message)
• _Static_assert(expression, message)

Parameters

Parameter Details

expression expression of scalar type.

message string literal to be included in the diagnostic message.

Remarks

Both assert and static_assert are macros defined in assert.h.

The definition of assert depends on the macro NDEBUG which is not defined by the standard library.
If NDEBUG is defined, assert is a no-op:

#ifdef NDEBUG
# define assert(condition) ((void) 0)
#else
# define assert(condition) /* implementation defined */
#endif

Opinion varies about whether NDEBUG should always be used for production compilations.

• The pro-camp argues that assert calls abort and assertion messages are not helpful for end
users, so the result is not helpful to user. If you have fatal conditions to check in production
code you should use ordinary if/else conditions and exit or quick_exit to end the program.
In contrast to abort, these allow the program to do some cleanup (via functions registered
with atexit or at_quick_exit).
• The con-camp argues that assert calls should never fire in production code, but if they do,
the condition that is checked means there is something dramatically wrong and the program

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