[assertions]

# 19 Diagnostics library [[diagnostics]](./#diagnostics)

## 19.3 Assertions [assertions]

### [19.3.1](#general) General [[assertions.general]](assertions.general)

[1](#general-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L452)

The header <cassert> provides a macro for documenting C++ program assertions and a mechanism
for disabling the assertion checks through defining the macro NDEBUG[.](#general-1.sentence-1)

### [19.3.2](#cassert.syn) Header <cassert> synopsis [[cassert.syn]](cassert.syn)

#define assert(...) *see below*

### [19.3.3](#assert) The assert macro [[assertions.assert]](assertions.assert)

[1](#assert-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L465)

If NDEBUG is defined as a macro name
at the point in the source file where <cassert> is included,
the assert macro is defined as#define assert(...) ((void)0)

[2](#assert-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L473)

Otherwise, the assert macro puts a diagnostic test into programs;
it expands to an expression of type void which
has the following effects:

- [(2.1)](#assert-2.1)

  __VA_ARGS__ is evaluated and contextually converted to bool[.](#assert-2.1.sentence-1)

- [(2.2)](#assert-2.2)

  If the evaluation yields true there are no further effects[.](#assert-2.2.sentence-1)

- [(2.3)](#assert-2.3)

  Otherwise, the assert macro's expression
creates a diagnostic on the standard error stream (ISO/IEC 9899:2024, 7.23.3) in animplementation-defined
format and calls abort()[.](#assert-2.3.sentence-1)
  The diagnostic contains #__VA_ARGS__ and
information on
the name of the source file,
the source line number, and
the name of the enclosing function
(such as provided by source_location​::​current())[.](#assert-2.3.sentence-2)

[3](#assert-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L496)

If __VA_ARGS__ does not expand to
an [*assignment-expression*](expr.assign#nt:assignment-expression "7.6.19 Assignment and compound assignment operators [expr.assign]"),
the program is ill-formed[.](#assert-3.sentence-1)

[4](#assert-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L501)

The macro assert is redefined according to
the current state of NDEBUG each time that<cassert> is included[.](#assert-4.sentence-1)

[5](#assert-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L506)

An expression assert(E) is a [constant subexpression](defns.const.subexpr "3.15 constant subexpression [defns.const.subexpr]"), if

- [(5.1)](#assert-5.1)

NDEBUG is defined at the point where assert is last defined or redefined, or

- [(5.2)](#assert-5.2)

E [contextually converted to bool](conv#def:conversion,contextual_to_bool "7.3 Standard conversions [conv]") is a constant subexpression that evaluates to the value true[.](#assert-5.sentence-1)