The assert() macro inserts diagnostics into applications. When executed, if expression is FALSE (zero), assert() prints the error message
Assertion failed: expression, file xyz, line nnn
on the standard error output and aborts. In the error message, xyz is the name of the source file and nnn the source line number of the assert() statement. These are respectively the values of the preprocessor macros __FILE__ and __LINE__.
Since assert() is implemented as a macro, the expression may not contain any string literals.
Compiling with the preprocessor option -DNDEBUG (see cc(1B)), or with the preprocessor control statement #define NDEBUG ahead of the #include <assert.h> statement, will stop assertions from being compiled into the program.
If the application is linked with -lintl, messages printed from this function are in the native language specified by the LC_MESSAGES locale category; see setlocale(3C).