assert

 

C++

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Error handling

Exception handling exception uncaught_exceptionuncaught_exceptions (C++17) exception_ptr (C++11) make_exception_ptr (C++11) current_exception (C++11) rethrow_exception (C++11) nested_exception (C++11) throw_with_nested (C++11) rethrow_if_nested (C++11) exception_list (C++17) Exception handling failures terminate terminate_handler get_terminate (C++11) set_terminate unexpected (deprecated) bad_exception unexpected_handler (deprecated) get_unexpected (C++11)(deprecated) set_unexpected (deprecated)

Exception categories logic_error invalid_argument domain_error length_error out_of_range runtime_error range_error overflow_error underflow_error Error codes Error codes errno Assertions assert system_error facility error_category (C++11) generic_category (C++11) system_category (C++11) error_condition (C++11) errc (C++11) error_code (C++11) system_error (C++11)

 

Defined in header <cassert>
#ifdef NDEBUG #define assert(condition) ((void)0) #else #define assert(condition) /*implementation defined*/ #endif

The definition of the macro assert depends on another macro, NDEBUG, which is not defined by the standard library.

If NDEBUG is defined as a macro name at the point in the source code where <cassert> is included, then assert does nothing.

If NDEBUG is not defined, then assert checks if its argument (which must have scalar type) compares equal to zero. If it does, assert outputs implementation-specific diagnostic information on the standard error output and calls std::abort. The diagnostic information is required to include the text of expression, as well as the values of the standard macros __FILE__, __LINE__, and the standard variable __func__.

The expression assert(E) is a constant subexpression, if either NDEBUG is defined at the point where assert is last defined or redefined (i.e., where the header <cassert> or <assert.h> was last included); or E, contextually converted to bool, is a constant subexpression that evaluates to true.

(since C++17)

Parameters

condition

-

expression of scalar type

Return value

(none)

Example

Run this code

#include <iostream>
// uncomment to disable assert()
// #define NDEBUG
#include <cassert>
 
int main()
{
    assert(2+2==4);
    std::cout << "Execution continues past the first assert\n";
    assert(2+2==5);
    std::cout << "Execution continues past the second assert\n";
}

Possible output:

Execution continues past the first assert
test: test.cc:10: int main(): Assertion `2+2==5' failed.
Aborted

See also

static assertion	performs compile-time assertion checking (since C++11)
abort	causes abnormal program termination (without cleaning up) (function)
C documentation for assert