GLib Reference Manual
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# Standard Macros

## Name

Standard Macros -- commonly-used macros.

## Synopsis

    #include <glib.h>

    #define     GLIB_MAJOR_VERSION
    #define     GLIB_MINOR_VERSION
    #define     GLIB_MICRO_VERSION

    #define     G_OS_WIN32
    #define     G_OS_BEOS
    #define     G_OS_UNIX

    #define     GLIB_CHECK_VERSION              (major,minor,micro)

    #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     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

### GLIB_MAJOR_VERSION

    #define GLIB_MAJOR_VERSION 2

The major version number of the GLib library.

### GLIB_MINOR_VERSION

    #define GLIB_MINOR_VERSION 0

The minor version number of the GLib library.

### GLIB_MICRO_VERSION

    #define GLIB_MICRO_VERSION 3

The micro version number of the GLib library.

### 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".

### GLIB_CHECK_VERSION()

    #define     GLIB_CHECK_VERSION(major,minor,micro)

Checks the version of the GLib library. It returns `TRUE` if the GLib library is the same or newer than the given version.

Example 1. Checking the version of the GLib library.

      if (!GLIB_CHECK_VERSION (1, 2, 0))
        g_error ("GLib version 1.2.0 or above is needed");

`major` : | the major version number.
`minor` : | the minor version number.
`micro` : | the micro version number.

### 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

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`.

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

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

### G_CONST_RETURN

    #define     G_CONST_RETURN

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.

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Limits of Basic Types | Type Conversion Macros