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__
(since C++11).
The expression
| (since C++17) |
condition | - | expression of scalar type |
(none).
Because assert
is a function-like macro, commas anywhere in condition that are not protected by parentheses are interpreted as macro argument separators. Such commas are often found in template argument lists and list-initialization:
assert(std::is_same_v<int, int>); // error: assert does not take two arguments assert((std::is_same_v<int, int>)); // OK: one argument static_assert(std::is_same_v<int, int>); // OK: not a macro std::complex<double> c; assert(c == std::complex<double>{0, 0}); // error assert((c == std::complex<double>{0, 0})); // OK
#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
static assertion | performs compile-time assertion checking (since C++11) |
causes abnormal program termination (without cleaning up) (function) |
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