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### 2.5 `assert`—macro for debugging diagnostics

Synopsis

    #include <assert.h>
    void assert(int expression);

Description
Use this macro to embed debuggging diagnostic statements in your programs. The argument expression should be an expression which evaluates to true (nonzero) when your program is working as you intended.

When expression evaluates to false (zero), `assert` calls `abort`, after first printing a message showing what failed and where:

     Assertion failed: expression, file filename, line lineno, function: func

If the name of the current function is not known (for example, when using a C89 compiler that does not understand __func__), the function location is omitted.

The macro is defined to permit you to turn off all uses of `assert` at compile time by defining `NDEBUG` as a preprocessor variable. If you do this, the `assert` macro expands to

     (void(0))

Returns
`assert` does not return a value.

Portability
The `assert` macro is required by ANSI, as is the behavior when `NDEBUG` is defined.

Supporting OS subroutines required (only if enabled): `close`, `fstat`, `getpid`, `isatty`, `kill`, `lseek`, `read`, `sbrk`, `write`.