Standard Macros

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

## Synopsis

    #include <glib.h>

    #define             G_OS_WIN32
    #define             G_OS_BEOS
    #define             G_OS_UNIX

    #define             G_DIR_SEPARATOR
    #define             G_DIR_SEPARATOR_S
    #define             G_IS_DIR_SEPARATOR                  (c)
    #define             G_SEARCHPATH_SEPARATOR
    #define             G_SEARCHPATH_SEPARATOR_S

    #define             TRUE
    #define             FALSE

    #define             NULL

    #define             MIN                                 (a,
                                                             b)
    #define             MAX                                 (a,
                                                             b)

    #define             ABS                                 (a)
    #define             CLAMP                               (x,
                                                             low,
                                                             high)

    #define             G_STRUCT_MEMBER                     (member_type,
                                                             struct_p,
                                                             struct_offset)
    #define             G_STRUCT_MEMBER_P                   (struct_p,
                                                             struct_offset)
    #define             G_STRUCT_OFFSET                     (struct_type,
                                                             member)

    #define             G_MEM_ALIGN

    #define             G_CONST_RETURN

## Description

These macros provide a few commonly-used features.

## Details

### 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_BEOS

    #define G_OS_BEOS

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

### 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_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.

`c` : | a character

Since 2.6

### 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.

### MIN()

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

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

`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`.

`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.

`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.

`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.

`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.

`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.

`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_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

### Warning

`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 should 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.