Standard Macros: GLib Reference Manual

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

## Functions

#define | G_IS_DIR_SEPARATOR()
#define | NULL
#define | MIN()
#define | MAX()
#define | ABS()
#define | CLAMP()
#define | G_STRUCT_MEMBER()
#define | G_STRUCT_MEMBER_P()
#define | G_STRUCT_OFFSET()
#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 | G_MEM_ALIGN
#define | G_CONST_RETURN

## 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

### NULL

    #  define NULL        (0L)

Defines the standard `NULL` pointer.

### 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_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_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.

### 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

`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.