GLib Reference Manual
<<< Previous Page | Home | Up | Next Page >>>

# Random Numbers

## Name

Random Numbers -- pseudo random number generator.

## Synopsis

    #include <glib.h>

    struct      GRand;
    GRand*      g_rand_new_with_seed            (guint32 seed);
    GRand*      g_rand_new                      (void);
    void        g_rand_free                     (GRand *rand);
    void        g_rand_set_seed                 (GRand *rand,
                                                 guint32 seed);
    #define     g_rand_boolean                  (rand)
    guint32     g_rand_int                      (GRand *rand);
    gint32      g_rand_int_range                (GRand *rand,
                                                 gint32 begin,
                                                 gint32 end);
    gdouble     g_rand_double                   (GRand *rand);
    gdouble     g_rand_double_range             (GRand *rand,
                                                 gdouble begin,
                                                 gdouble end);
    void        g_random_set_seed               (guint32 seed);
    #define     g_random_boolean                ()
    guint32     g_random_int                    (void);
    gint32      g_random_int_range              (gint32 begin,
                                                 gint32 end);
    gdouble     g_random_double                 (void);
    gdouble     g_random_double_range           (gdouble begin,
                                                 gdouble end);

## Description

The following functions allow you to use a portable, fast and good pseudo random number generator (PRNG). It uses the Mersenne Twister PRNG, which was originally developed by Makoto Matsumoto and Takuji Nishimura. Further information can be found at www.math.keio.ac.jp/~matumoto/emt.html.

If you just need a random number, you simply call the `g_random_*` functions, which will create a globally used GRand and use the according `g_rand_*` functions internally. Whenever you need a stream of reproducible random numbers, you better create a GRand yourself and use the `g_rand_*` functions directly, which will also be slightly faster. Initializing a GRand with a certain seed will produce exactly the same series of random numbers on all platforms. This can thus be used as a seed for e.g. games.

The `g_rand*_range` functions will return high quality equally distributed random numbers, whereas for example the `(g_random_int()%`max`)` approach often doesn't yield equally distributed numbers.

## Details

### struct GRand

    struct GRand;

The GRand struct is an opaque data structure. It should only be accessed through the `g_rand_*` functions.

### g_rand_new_with_seed ()

    GRand*      g_rand_new_with_seed            (guint32 seed);

Creates a new random number generator initialized with `seed`.

`seed` : | a value to initialize the random number generator.
Returns : | the new GRand.

### g_rand_new ()

    GRand*      g_rand_new                      (void);

Creates a new random number generator initialized with a seed taken either from `/dev/urandom` (if existing) or from the current time (as a fallback).

Returns : | the new GRand.

### g_rand_free ()

    void        g_rand_free                     (GRand *rand);

Frees the memory allocated for the GRand.

`rand` : | a GRand.

### g_rand_set_seed ()

    void        g_rand_set_seed                 (GRand *rand,
                                                 guint32 seed);

Sets the seed for the random number generator GRand to `seed`.

`rand` : | a GRand.
`seed` : | a value to reinitialize the random number generator.

### g_rand_boolean()

    #define     g_rand_boolean(rand)

Returns a random gboolean from `rand`. This corresponds to a unbiased coin toss.

`rand` : | a GRand.
Returns : | a random gboolean.

### g_rand_int ()

    guint32     g_rand_int                      (GRand *rand);

Returns the next random guint32 from `rand` equally distributed over the range [0..2^32-1].

`rand` : | a GRand.
Returns : | A random number.

### g_rand_int_range ()

    gint32      g_rand_int_range                (GRand *rand,
                                                 gint32 begin,
                                                 gint32 end);

Returns the next random gint32 from `rand` equally distributed over the range [`begin`..`end`-1].

`rand` : | a GRand.
`begin` : | lower closed bound of the interval.
`end` : | upper open bound of the interval.
Returns : | A random number.

### g_rand_double ()

    gdouble     g_rand_double                   (GRand *rand);

Returns the next random gdouble from `rand` equally distributed over the range [0..1).

`rand` : | a GRand.
Returns : | A random number.

### g_rand_double_range ()

    gdouble     g_rand_double_range             (GRand *rand,
                                                 gdouble begin,
                                                 gdouble end);

Returns the next random gdouble from `rand` equally distributed over the range [`begin`..`end`).

`rand` : | a GRand.
`begin` : | lower closed bound of the interval.
`end` : | upper open bound of the interval.
Returns : | A random number.

### g_random_set_seed ()

    void        g_random_set_seed               (guint32 seed);

Sets the seed for the global random number generator, which is used by the `g_random_*` functions, to `seed`.

`seed` : | a value to reinitialize the global random number generator.

### g_random_boolean()

    #define     g_random_boolean()

Returns a random gboolean. This corresponds to a unbiased coin toss.

Returns : | a random gboolean.

### g_random_int ()

    guint32     g_random_int                    (void);

Return a random guint32 equally distributed over the range [0..2^32-1].

Returns : | A random number.

### g_random_int_range ()

    gint32      g_random_int_range              (gint32 begin,
                                                 gint32 end);

Returns a random gint32 equally distributed over the range [`begin`..`end`-1].

`begin` : | lower closed bound of the interval.
`end` : | upper open bound of the interval.
Returns : | A random number.

### g_random_double ()

    gdouble     g_random_double                 (void);

Returns a random gdouble equally distributed over the range [0..1).

Returns : | A random number.

### g_random_double_range ()

    gdouble     g_random_double_range           (gdouble begin,
                                                 gdouble end);

Returns a random gdouble equally distributed over the range [`begin`..`end`).

`begin` : | lower closed bound of the interval.
`end` : | upper open bound of the interval.
Returns : | A random number.

<<< Previous Page | Home | Up | Next Page >>>
Date and Time Functions | Hook Functions