Most of the standard library facilities are supported. Some of them—the ones that need an operating system—require a low-level implementation in the application. For more information, see The DLIB runtime environment.

The assert() function prints:

filename:linenr expression ‑‑ assertion failed

when the parameter evaluates to zero.

For information about the floating-point status flags, see fenv.h.

For information about the feraiseexcept function raising floating-point exceptions, see Floating-point environment.

For information about strings passed to the setlocale function, see Locale.

The FLT_EVAL_METHOD macro can only have the value 0.

No function generates other domain errors than what the standard requires.

Mathematic functions return a floating-point NaN (not a number) for domain errors.

Mathematic functions set errno to the macro ERANGE (a macro in errno.h) and return zero for underflow errors.

The fmod function sets errno to a domain error and returns a floating-point NaN when the second argument is zero.

The remainder function sets errno to a domain error and returns a floating-point NaN when the second argument is zero.

The magnitude is congruent modulo INT_MAX.

The remquo function sets errno to a domain error and returns a floating-point NaN when the second argument is zero.

The signal part of the library is not supported.

The NULL macro is defined to 0.

Stream functions recognize either newline or endoffile(EOF) as the terminating character for a line.

Space characters written to a stream immediately before a newline character are preserved.

No null characters are appended to data written to binary streams.

The file position is initially placed at the beginning of the file when it is opened in append-mode.

Whether a write operation on a text stream causes the associated file to be truncated beyond that point, depends on the application-specific implementation of the low-level file routines. See Briefly about input and output (I/O).

An open file can be either block-buffered, line-buffered, or unbuffered.

Whether a zero-length file exists depends on the application-specific implementation of the low-level file routines.

The legality of a filename depends on the application-specific implementation of the low-level file routines.

Whether a file can be opened more than once depends on the application-specific implementation of the low-level file routines.

The encoding of multibyte characters in a file depends on the application-specific implementation of the low-level file routines.

The effect of a remove operation on an open file depends on the application-specific implementation of the low-level file routines. See Briefly about input and output (I/O).

The effect of renaming a file to an already existing filename depends on the application-specific implementation of the low-level file routines. See Briefly about input and output (I/O).

Whether an open temporary file is removed depends on the application-specific implementation of the low-level file routines.

freopen closes the named stream, then reopens it in the new mode. The streams stdin, stdout, and stderr can be reopened in any new mode.

The style used for printing infinity or NaN for a floating-point constant is inf and nan (INF and NAN for the F conversion specifier), respectively. The n-char-sequence is not used for nan.

The argument to a %p conversion specifier, print pointer, to printf() is treated as having the type void *. The value will be printed as a hexadecimal number, similar to using the %x conversion specifier.

A - (dash) character is always treated as a range symbol.

The %p conversion specifier, scan pointer, to scanf() reads a hexadecimal number and converts it into a value with the type void *.

On file position errors, the functions fgetpos, ftell, and fsetpos store EFPOS in errno.

An n-char-sequence after a NaN is read and ignored.

errno is set to ERANGE if an underflow is encountered.

A request for a zero-sized heap object will return a valid pointer and not a null pointer.

A call to abort() or _Exit() will not flush stream buffers, not close open streams, and not remove temporary files.

The termination status will be propagated to __exit() as a parameter. exit(), _Exit(), and quick_exit use the input parameter, whereas abort uses EXIT_FAILURE.

The system function returns -1 when its argument is not a null pointer.

The range and precision of clock_t is up to your implementation. The range and precision of time_t is 19000101 up to 20351231 in tics of a second if the 32-bit time_t is used. It is -9999 up to 9999 years in tics of a second if the 64-bit time_t is used. See time.h

The local time zone and daylight savings time must be defined by the application. For more information, see time.h.

The era for the clock function is up to your implementation.

The epoch for TIME_UTC is up to your implementation.

By default, ":" or "" (an empty string) is used as a replacement for %Z. Your application should implement the time zone handling. See __time32, __time64.

The functions in math.h honor the rounding direction mode in FLT-ROUNDS.