19 Diagnostics library [diagnostics]

19.3 Assertions [assertions]

19.3.1 General [assertions.general]

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The header <cassert> provides a macro for documenting C++ program assertions and a mechanism for disabling the assertion checks through defining the macro NDEBUG.

19.3.2 Header <cassert> synopsis [cassert.syn]

#define assert(...) see below

19.3.3 The assert macro [assertions.assert]

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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)
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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)
    __VA_ARGS__ is evaluated and contextually converted to bool.
  • (2.2)
    If the evaluation yields true there are no further effects.
  • (2.3)
    Otherwise, the assert macro's expression creates a diagnostic on the standard error stream (ISO/IEC 9899:2018, 7.23.3) in an implementation-defined format and calls abort().
    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()).
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If __VA_ARGS__ does not expand to an assignment-expression, the program is ill-formed.
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The macro assert is redefined according to the current state of NDEBUG each time that <cassert> is included.
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An expression assert(E) is a constant subexpression, if