Standard Macros: GLib Reference Manual

## Standard Macros Standard Macros — commonly-used macros |

## Functions

#define | G_IS_DIR_SEPARATOR()
#define | MIN()
#define | MAX()
#define | ABS()
#define | CLAMP()
#define | G_APPROX_VALUE()
#define | G_SIZEOF_MEMBER()
#define | G_STRUCT_MEMBER()
#define | G_STRUCT_MEMBER_P()
#define | G_STRUCT_OFFSET()
#define | G_ALIGNOF()
#define | G_N_ELEMENTS()

## Types and Values

#define | G_OS_WIN32
#define | G_OS_UNIX
#define | G_DIR_SEPARATOR
#define | G_DIR_SEPARATOR_S
#define | G_SEARCHPATH_SEPARATOR
#define | G_SEARCHPATH_SEPARATOR_S
#define | TRUE
#define | FALSE
#define | NULL
#define | G_MEM_ALIGN
#define | G_CONST_RETURN
#define | G_NORETURN
#define | G_NORETURN_FUNCPTR

## Includes

    #include <glib.h>

## Description

These macros provide a few commonly-used features.

## Functions

### G_IS_DIR_SEPARATOR()

    #define G_IS_DIR_SEPARATOR(c) ((c) == G_DIR_SEPARATOR || (c) == '/')

Checks whether a character is a directory separator. It returns `TRUE` for '/' on UNIX machines and for '\' or '/' under Windows.

#### Parameters

c | a character |

Since: 2.6

### MIN()

    #define MIN(a, b)  (((a) < (b)) ? (a) : (b))

Calculates the minimum of `a` and `b` .

#### Parameters

a | a numeric value |
b | a numeric value |

#### Returns

the minimum of `a` and `b` .

### MAX()

    #define MAX(a, b)  (((a) > (b)) ? (a) : (b))

Calculates the maximum of `a` and `b` .

#### Parameters

a | a numeric value |
b | a numeric value |

#### Returns

the maximum of `a` and `b` .

### ABS()

    #define ABS(a)	   (((a) < 0) ? -(a) : (a))

Calculates the absolute value of `a` . The absolute value is simply the number with any negative sign taken away.

For example,

- ABS(-10) is 10.

- ABS(10) is also 10.

#### Parameters

a | a numeric value |

#### Returns

the absolute value of `a` .

### CLAMP()

    #define CLAMP(x, low, high)  (((x) > (high)) ? (high) : (((x) < (low)) ? (low) : (x)))

Ensures that `x` is between the limits set by `low` and `high` . If `low` is greater than `high` the result is undefined.

For example,

- CLAMP(5, 10, 15) is 10.

- CLAMP(15, 5, 10) is 10.

- CLAMP(20, 15, 25) is 20.

#### Parameters

x | the value to clamp |
low | the minimum value allowed |
high | the maximum value allowed |

#### Returns

the value of `x` clamped to the range between `low` and `high`

### G_APPROX_VALUE()

    #define             G_APPROX_VALUE(a, b, epsilon)

Evaluates to a truth value if the absolute difference between `a` and `b` is smaller than `epsilon` , and to a false value otherwise.

For example,

- `G_APPROX_VALUE (5, 6, 2)` evaluates to true

- `G_APPROX_VALUE (3.14, 3.15, 0.001)` evaluates to false

- `G_APPROX_VALUE (n, 0.f, FLT_EPSILON)` evaluates to true if `n` is within the single precision floating point epsilon from zero

#### Parameters

a | a numeric value |
b | a numeric value |
epsilon | a numeric value that expresses the tolerance between `a` and `b` |

#### Returns

`TRUE` if the two values are within the desired range

Since: 2.58

### G_SIZEOF_MEMBER()

    #define             G_SIZEOF_MEMBER(struct_type, member)

Returns the size of `member` in the struct definition without having a declared instance of `struct_type` .

#### Parameters

struct_type | a structure type, e.g. GOutputVector |
member | a field in the structure, e.g. `size` |

#### Returns

the size of `member` in bytes.

Since: 2.64

### G_STRUCT_MEMBER()

    #define             G_STRUCT_MEMBER(member_type, struct_p, struct_offset)

Returns a member of a structure at a given offset, using the given type.

#### Parameters

member_type | the type of the struct field |
struct_p | a pointer to a struct |
struct_offset | the offset of the field from the start of the struct, in bytes |

#### Returns

the struct member

### G_STRUCT_MEMBER_P()

    #define             G_STRUCT_MEMBER_P(struct_p, struct_offset)

Returns an untyped pointer to a given offset of a struct.

#### Parameters

struct_p | a pointer to a struct |
struct_offset | the offset from the start of the struct, in bytes |

#### Returns

an untyped pointer to `struct_p` plus `struct_offset` bytes

### G_STRUCT_OFFSET()

    #define             G_STRUCT_OFFSET(struct_type, member)

Returns the offset, in bytes, of a member of a struct.

#### Parameters

struct_type | a structure type, e.g. GtkWidget |
member | a field in the structure, e.g. `window` |

#### Returns

the offset of `member` from the start of `struct_type`

### G_ALIGNOF()

    #define             G_ALIGNOF(type)

Return the minimal alignment required by the platform ABI for values of the given type. The address of a variable or struct member of the given type must always be a multiple of this alignment. For example, most platforms require int variables to be aligned at a 4-byte boundary, so `G_ALIGNOF (int)` is 4 on most platforms.

Note this is not necessarily the same as the value returned by GCC’s `__alignof__` operator, which returns the preferred alignment for a type. The preferred alignment may be a stricter alignment than the minimal alignment.

#### Parameters

type | a type-name |

Since: 2.60

### G_N_ELEMENTS()

    #define G_N_ELEMENTS(arr)		(sizeof (arr) / sizeof ((arr)[0]))

Determines the number of elements in an array. The array must be declared so the compiler knows its size at compile-time; this macro will not work on an array allocated on the heap, only static arrays or arrays on the stack.

#### Parameters

arr | the array |

## Types and Values

### G_OS_WIN32

    #define G_OS_WIN32

This macro is defined only on Windows. So you can bracket Windows-specific code in "#ifdef G_OS_WIN32".

### G_OS_UNIX

    #define G_OS_UNIX

This macro is defined only on UNIX. So you can bracket UNIX-specific code in "#ifdef G_OS_UNIX".

### G_DIR_SEPARATOR

    #define G_DIR_SEPARATOR '/'

The directory separator character. This is '/' on UNIX machines and '\' under Windows.

### G_DIR_SEPARATOR_S

    #define G_DIR_SEPARATOR_S "/"

The directory separator as a string. This is "/" on UNIX machines and "\" under Windows.

### G_SEARCHPATH_SEPARATOR

    #define G_SEARCHPATH_SEPARATOR ':'

The search path separator character. This is ':' on UNIX machines and ';' under Windows.

### G_SEARCHPATH_SEPARATOR_S

    #define G_SEARCHPATH_SEPARATOR_S ":"

The search path separator as a string. This is ":" on UNIX machines and ";" under Windows.

### TRUE

    #define TRUE (!FALSE)

Defines the `TRUE` value for the gboolean type.

### FALSE

    #define FALSE (0)

Defines the `FALSE` value for the gboolean type.

### NULL

    #  define NULL        (0L)

Defines the standard `NULL` pointer.

### G_MEM_ALIGN

    #  define G_MEM_ALIGN GLIB_SIZEOF_VOID_P

Indicates the number of bytes to which memory will be aligned on the current platform.

### G_CONST_RETURN

    #define G_CONST_RETURN GLIB_DEPRECATED_MACRO_IN_2_30_FOR(const)

`G_CONST_RETURN` has been deprecated since version 2.30 and should not be used in newly-written code.

API providers should replace all existing uses with const and API consumers should adjust their code accordingly

If `G_DISABLE_CONST_RETURNS` is defined, this macro expands to nothing. By default, the macro expands to const. The macro can be used in place of const for functions that return a value that should not be modified. The purpose of this macro is to allow us to turn on const for returned constant strings by default, while allowing programmers who find that annoying to turn it off. This macro should only be used for return values and for "out" parameters, it doesn't make sense for "in" parameters.

### G_NORETURN

    # define G_NORETURN __attribute__ ((__noreturn__))

Expands to the GNU C or MSVC `noreturn` function attribute depending on the compiler. It is used for declaring functions which never return. Enables optimization of the function, and avoids possible compiler warnings.

Note that `G_NORETURN` supersedes the previous `G_GNUC_NORETURN` macro, which will eventually be deprecated. `G_NORETURN` supports more platforms.

Place the attribute before the function declaration as follows:

    1
    G_NORETURN void g_abort (void);

Since: 2.68

### G_NORETURN_FUNCPTR

    #define             G_NORETURN_FUNCPTR

Expands to the GNU C or MSVC `noreturn` function attribute depending on the compiler. It is used for declaring function pointers which never return. Enables optimization of the function, and avoids possible compiler warnings.

Place the attribute before the function declaration as follows:

    1
    G_NORETURN_FUNCPTR void (*funcptr) (void);

Note that if the function is not a function pointer, you can simply use the `G_NORETURN` macro as follows:

    1
    G_NORETURN void g_abort (void);

Since: 2.68