optional.h File Reference

C analog of C++’s std::optional More...

#include <assert.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>

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Macros
#define	OPTIONAL(type)
	a container that may or may not contain a value
#define	OPTIONAL_SET(me, value)
#define	OPTIONAL_VALUE(me)
#define	OPTIONAL_VALUE_OR(me, fallback)    ((me).has_value ? (me).value_ : (fallback))

Macro Definition Documentation

OPTIONAL

#define OPTIONAL

(

type

)

Value:

  struct {                                                                     \
    bool has_value;                             \
    type value_;                       \
  }

Definition at line 13 of file optional.h.

OPTIONAL_SET

#define OPTIONAL_SET	(		me,
			value
	)

Value:

  do {                                                                         \
    assert((me) != NULL);                                                      \
    (me)->has_value = true;                                                    \
    (me)->value_ = (value);                                                    \
  } while (0)

set the value of an optional

This utility macro is intended to avoid the easy typo of setting the value while forgetting to set the has_value member.

Parameters

me	The optional whose value to set
value	The value to assign

Definition at line 26 of file optional.h.

OPTIONAL_VALUE

#define OPTIONAL_VALUE

(

me

)

Value:

  (((me).has_value ? (void)0                                                   \
                   : (fprintf(stderr,                                          \
                              "%s:%d: internal error: attempted to read the "  \
                              "value of an empty optional type\n",             \
                              __FILE__, __LINE__),                             \
                      abort())),                                               \
   (me).value_)

get the value of an optional

The caller must know the optional has a value before calling this.

Parameters

me	The optional whose value to retrieve

Returns

Value of the optional

Definition at line 39 of file optional.h.

OPTIONAL_VALUE_OR

#define OPTIONAL_VALUE_OR	(		me,
			fallback
	)		((me).has_value ? (me).value_ : (fallback))

get the value of an optional or a given value if the optional is empty

Parameters

me	The optional whose value to retrieve
fallback	The value to return if the optional is empty

Returns

Value of the optional or fallback if it was empty

Definition at line 53 of file optional.h.