## Memory Allocation

Memory Allocation — general memory-handling

## Functions

#define | g_new()
#define | g_new0()
#define | g_renew()
#define | g_try_new()
#define | g_try_new0()
#define | g_try_renew()
gpointer | g_malloc ()
gpointer | g_malloc0 ()
gpointer | g_realloc ()
gpointer | g_try_malloc ()
gpointer | g_try_malloc0 ()
gpointer | g_try_realloc ()
gpointer | g_malloc_n ()
gpointer | g_malloc0_n ()
gpointer | g_realloc_n ()
gpointer | g_try_malloc_n ()
gpointer | g_try_malloc0_n ()
gpointer | g_try_realloc_n ()
void | g_free ()
void | g_clear_pointer ()
gpointer | g_steal_pointer ()
#define | g_alloca()
#define | g_newa()
#define | g_memmove()
gpointer | g_memdup ()
void | g_mem_set_vtable ()
gboolean | g_mem_is_system_malloc ()
void | g_mem_profile ()

## Types and Values

extern gboolean | g_mem_gc_friendly
struct | GMemVTable
extern GMemVTable * | glib_mem_profiler_table

## Includes

    #include <glib.h>

## Description

These functions provide support for allocating and freeing memory.

If any call to allocate memory using functions `g_new()`, `g_new0()`, `g_renew()`, `g_malloc()`, `g_malloc0()`, `g_malloc0_n()`, `g_realloc()`, and `g_realloc_n()` fails, the application is terminated. This also means that there is no need to check if the call succeeded. On the other hand, g_try_...() family of functions returns `NULL` on failure that can be used as a check for unsuccessful memory allocation. The application is not terminated in this case.

It's important to match `g_malloc()` (and wrappers such as `g_new()`) with `g_free()`, `g_slice_alloc()` (and wrappers such as `g_slice_new()`) with `g_slice_free()`, plain `malloc()` with `free()`, and (if you're using C++) new with delete and new[] with delete[]. Otherwise bad things can happen, since these allocators may use different memory pools (and new/delete call constructors and destructors).

## Functions

### g_new()

    #define             g_new(struct_type, n_structs)

Allocates `n_structs` elements of type `struct_type` . The returned pointer is cast to a pointer to the given type. If `n_structs` is 0 it returns `NULL`. Care is taken to avoid overflow when calculating the size of the allocated block.

Since the returned pointer is already casted to the right type, it is normally unnecessary to cast it explicitly, and doing so might hide memory allocation errors.

#### Parameters

struct_type | the type of the elements to allocate |
n_structs | the number of elements to allocate |

#### Returns

a pointer to the allocated memory, cast to a pointer to `struct_type`

### g_new0()

    #define             g_new0(struct_type, n_structs)

Allocates `n_structs` elements of type `struct_type` , initialized to 0's. The returned pointer is cast to a pointer to the given type. If `n_structs` is 0 it returns `NULL`. Care is taken to avoid overflow when calculating the size of the allocated block.

Since the returned pointer is already casted to the right type, it is normally unnecessary to cast it explicitly, and doing so might hide memory allocation errors.

#### Parameters

struct_type | the type of the elements to allocate. |
n_structs | the number of elements to allocate. |

#### Returns

a pointer to the allocated memory, cast to a pointer to `struct_type` .

### g_renew()

    #define             g_renew(struct_type, mem, n_structs)

Reallocates the memory pointed to by `mem` , so that it now has space for `n_structs` elements of type `struct_type` . It returns the new address of the memory, which may have been moved. Care is taken to avoid overflow when calculating the size of the allocated block.

#### Parameters

struct_type | the type of the elements to allocate |
mem | the currently allocated memory |
n_structs | the number of elements to allocate |

#### Returns

a pointer to the new allocated memory, cast to a pointer to `struct_type`

### g_try_new()

    #define             g_try_new(struct_type, n_structs)

Attempts to allocate `n_structs` elements of type `struct_type` , and returns `NULL` on failure. Contrast with `g_new()`, which aborts the program on failure. The returned pointer is cast to a pointer to the given type. The function returns `NULL` when `n_structs` is 0 of if an overflow occurs.

#### Parameters

struct_type | the type of the elements to allocate |
n_structs | the number of elements to allocate |

#### Returns

a pointer to the allocated memory, cast to a pointer to `struct_type`

Since: 2.8

### g_try_new0()

    #define             g_try_new0(struct_type, n_structs)

Attempts to allocate `n_structs` elements of type `struct_type` , initialized to 0's, and returns `NULL` on failure. Contrast with `g_new0()`, which aborts the program on failure. The returned pointer is cast to a pointer to the given type. The function returns `NULL` when `n_structs` is 0 or if an overflow occurs.

#### Parameters

struct_type | the type of the elements to allocate |
n_structs | the number of elements to allocate |

#### Returns

a pointer to the allocated memory, cast to a pointer to `struct_type`

Since: 2.8

### g_try_renew()

    #define             g_try_renew(struct_type, mem, n_structs)

Attempts to reallocate the memory pointed to by `mem` , so that it now has space for `n_structs` elements of type `struct_type` , and returns `NULL` on failure. Contrast with `g_renew()`, which aborts the program on failure. It returns the new address of the memory, which may have been moved. The function returns `NULL` if an overflow occurs.

#### Parameters

struct_type | the type of the elements to allocate |
mem | the currently allocated memory |
n_structs | the number of elements to allocate |

#### Returns

a pointer to the new allocated memory, cast to a pointer to `struct_type`

Since: 2.8

### g_malloc ()

    gpointer
    g_malloc (gsize n_bytes);

Allocates `n_bytes` bytes of memory. If `n_bytes` is 0 it returns `NULL`.

#### Parameters

n_bytes | the number of bytes to allocate |

#### Returns

a pointer to the allocated memory

### g_malloc0 ()

    gpointer
    g_malloc0 (gsize n_bytes);

Allocates `n_bytes` bytes of memory, initialized to 0's. If `n_bytes` is 0 it returns `NULL`.

#### Parameters

n_bytes | the number of bytes to allocate |

#### Returns

a pointer to the allocated memory

### g_realloc ()

    gpointer
    g_realloc (gpointer mem,
               gsize n_bytes);

Reallocates the memory pointed to by `mem` , so that it now has space for `n_bytes` bytes of memory. It returns the new address of the memory, which may have been moved. `mem` may be `NULL`, in which case it's considered to have zero-length. `n_bytes` may be 0, in which case `NULL` will be returned and `mem` will be freed unless it is `NULL`.

#### Parameters

mem | the memory to reallocate. | [nullable]
n_bytes | new size of the memory in bytes |

#### Returns

the new address of the allocated memory

### g_try_malloc ()

    gpointer
    g_try_malloc (gsize n_bytes);

Attempts to allocate `n_bytes` , and returns `NULL` on failure. Contrast with `g_malloc()`, which aborts the program on failure.

#### Parameters

n_bytes | number of bytes to allocate. |

#### Returns

the allocated memory, or `NULL`.

### g_try_malloc0 ()

    gpointer
    g_try_malloc0 (gsize n_bytes);

Attempts to allocate `n_bytes` , initialized to 0's, and returns `NULL` on failure. Contrast with `g_malloc0()`, which aborts the program on failure.

#### Parameters

n_bytes | number of bytes to allocate |

#### Returns

the allocated memory, or `NULL`

Since: 2.8

### g_try_realloc ()

    gpointer
    g_try_realloc (gpointer mem,
                   gsize n_bytes);

Attempts to realloc `mem` to a new size, `n_bytes` , and returns `NULL` on failure. Contrast with `g_realloc()`, which aborts the program on failure.

If `mem` is `NULL`, behaves the same as `g_try_malloc()`.

#### Parameters

mem | previously-allocated memory, or `NULL`. | [nullable]
n_bytes | number of bytes to allocate. |

#### Returns

the allocated memory, or `NULL`.

### g_malloc_n ()

    gpointer
    g_malloc_n (gsize n_blocks,
                gsize n_block_bytes);

This function is similar to `g_malloc()`, allocating (`n_blocks` * `n_block_bytes` ) bytes, but care is taken to detect possible overflow during multiplication.

#### Parameters

n_blocks | the number of blocks to allocate |
n_block_bytes | the size of each block in bytes |

#### Returns

a pointer to the allocated memory

Since: 2.24

### g_malloc0_n ()

    gpointer
    g_malloc0_n (gsize n_blocks,
                 gsize n_block_bytes);

This function is similar to `g_malloc0()`, allocating (`n_blocks` * `n_block_bytes` ) bytes, but care is taken to detect possible overflow during multiplication.

#### Parameters

n_blocks | the number of blocks to allocate |
n_block_bytes | the size of each block in bytes |

#### Returns

a pointer to the allocated memory

Since: 2.24

### g_realloc_n ()

    gpointer
    g_realloc_n (gpointer mem,
                 gsize n_blocks,
                 gsize n_block_bytes);

This function is similar to `g_realloc()`, allocating (`n_blocks` * `n_block_bytes` ) bytes, but care is taken to detect possible overflow during multiplication.

#### Parameters

mem | the memory to reallocate. | [nullable]
n_blocks | the number of blocks to allocate |
n_block_bytes | the size of each block in bytes |

#### Returns

the new address of the allocated memory

Since: 2.24

### g_try_malloc_n ()

    gpointer
    g_try_malloc_n (gsize n_blocks,
                    gsize n_block_bytes);

This function is similar to `g_try_malloc()`, allocating (`n_blocks` * `n_block_bytes` ) bytes, but care is taken to detect possible overflow during multiplication.

#### Parameters

n_blocks | the number of blocks to allocate |
n_block_bytes | the size of each block in bytes |

#### Returns

the allocated memory, or `NULL`.

Since: 2.24

### g_try_malloc0_n ()

    gpointer
    g_try_malloc0_n (gsize n_blocks,
                     gsize n_block_bytes);

This function is similar to `g_try_malloc0()`, allocating (`n_blocks` * `n_block_bytes` ) bytes, but care is taken to detect possible overflow during multiplication.

#### Parameters

n_blocks | the number of blocks to allocate |
n_block_bytes | the size of each block in bytes |

#### Returns

the allocated memory, or `NULL`

Since: 2.24

### g_try_realloc_n ()

    gpointer
    g_try_realloc_n (gpointer mem,
                     gsize n_blocks,
                     gsize n_block_bytes);

This function is similar to `g_try_realloc()`, allocating (`n_blocks` * `n_block_bytes` ) bytes, but care is taken to detect possible overflow during multiplication.

#### Parameters

mem | previously-allocated memory, or `NULL`. | [nullable]
n_blocks | the number of blocks to allocate |
n_block_bytes | the size of each block in bytes |

#### Returns

the allocated memory, or `NULL`.

Since: 2.24

### g_free ()

    void
    g_free (gpointer mem);

Frees the memory pointed to by `mem` .

If `mem` is `NULL` it simply returns, so there is no need to check `mem` against `NULL` before calling this function.

#### Parameters

mem | the memory to free. | [nullable]

### g_clear_pointer ()

    void
    g_clear_pointer (gpointer *pp,
                     GDestroyNotify destroy);

Clears a reference to a variable.

`pp` must not be `NULL`.

If the reference is `NULL` then this function does nothing. Otherwise, the variable is destroyed using `destroy` and the pointer is set to `NULL`.

A macro is also included that allows this function to be used without pointer casts.

[skip]

#### Parameters

pp | a pointer to a variable, struct member etc. holding a pointer. | [not nullable]
destroy | a function to which a gpointer can be passed, to destroy *`pp` |

Since: 2.34

### g_steal_pointer ()

    gpointer
    g_steal_pointer (gpointer pp);

Sets `pp` to `NULL`, returning the value that was there before.

Conceptually, this transfers the ownership of the pointer from the referenced variable to the "caller" of the macro (ie: "steals" the reference).

The return value will be properly typed, according to the type of `pp` .

This can be very useful when combined with `g_autoptr()` to prevent the return value of a function from being automatically freed. Consider the following example (which only works on GCC and clang):

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    GObject *
    create_object (void)
    {
      g_autoptr(GObject) obj = g_object_new (G_TYPE_OBJECT, NULL);

      if (early_error_case)
        return NULL;

      return g_steal_pointer (&obj);
    }

It can also be used in similar ways for 'out' parameters and is particularly useful for dealing with optional out parameters:

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    gboolean
    get_object (GObject **obj_out)
    {
      g_autoptr(GObject) obj = g_object_new (G_TYPE_OBJECT, NULL);

      if (early_error_case)
        return FALSE;

      if (obj_out)
        *obj_out = g_steal_pointer (&obj);

      return TRUE;
    }

In the above example, the object will be automatically freed in the early error case and also in the case that `NULL` was given for `obj_out` .

#### Parameters

pp | a pointer to a pointer. | [not nullable]

Since: 2.44

### g_alloca()

    #define             g_alloca(size)

Allocates `size` bytes on the stack; these bytes will be freed when the current stack frame is cleaned up. This macro essentially just wraps the `alloca()` function present on most UNIX variants. Thus it provides the same advantages and pitfalls as `alloca()`:

- alloca() is very fast, as on most systems it's implemented by just adjusting the stack pointer register.

- It doesn't cause any memory fragmentation, within its scope, separate `alloca()` blocks just build up and are released together at function end.

- Allocation sizes have to fit into the current stack frame. For instance in a threaded environment on Linux, the per-thread stack size is limited to 2 Megabytes, so be sparse with `alloca()` uses.

- Allocation failure due to insufficient stack space is not indicated with a `NULL` return like e.g. with `malloc()`. Instead, most systems probably handle it the same way as out of stack space situations from infinite function recursion, i.e. with a segmentation fault.

- Special care has to be taken when mixing `alloca()` with GNU C variable sized arrays. Stack space allocated with `alloca()` in the same scope as a variable sized array will be freed together with the variable sized array upon exit of that scope, and not upon exit of the enclosing function scope.

#### Parameters

size | number of bytes to allocate. |

#### Returns

space for `size` bytes, allocated on the stack

### g_newa()

    #define             g_newa(struct_type, n_structs)

Wraps `g_alloca()` in a more typesafe manner.

#### Parameters

struct_type | Type of memory chunks to be allocated |
n_structs | Number of chunks to be allocated |

#### Returns

Pointer to stack space for `n_structs` chunks of type `struct_type`

### g_memmove()

    #define             g_memmove(dest,src,len)

`g_memmove` has been deprecated since version 2.40 and should not be used in newly-written code.

Just use `memmove()`.

Copies a block of memory `len` bytes long, from `src` to `dest` . The source and destination areas may overlap.

#### Parameters

dest | the destination address to copy the bytes to. |
src | the source address to copy the bytes from. |
len | the number of bytes to copy. |

### g_memdup ()

    gpointer
    g_memdup (gconstpointer mem,
              guint byte_size);

Allocates `byte_size` bytes of memory, and copies `byte_size` bytes into it from `mem` . If `mem` is `NULL` it returns `NULL`.

#### Parameters

mem | the memory to copy. |
byte_size | the number of bytes to copy. |

#### Returns

a pointer to the newly-allocated copy of the memory, or `NULL` if `mem` is `NULL`.

### g_mem_set_vtable ()

    void
    g_mem_set_vtable (GMemVTable *vtable);

`g_mem_set_vtable` has been deprecated since version 2.46 and should not be used in newly-written code.

This function now does nothing. Use other memory profiling tools instead

This function used to let you override the memory allocation function. However, its use was incompatible with the use of global constructors in GLib and GIO, because those use the GLib allocators before main is reached. Therefore this function is now deprecated and is just a stub.

#### Parameters

vtable | table of memory allocation routines. |

### g_mem_is_system_malloc ()

    gboolean
    g_mem_is_system_malloc (void);

`g_mem_is_system_malloc` has been deprecated since version 2.46 and should not be used in newly-written code.

GLib always uses the system malloc, so this function always returns `TRUE`.

Checks whether the allocator used by `g_malloc()` is the system's malloc implementation. If it returns `TRUE` memory allocated with `malloc()` can be used interchangeable with memory allocated using `g_malloc()`. This function is useful for avoiding an extra copy of allocated memory returned by a non-GLib-based API.

#### Returns

if `TRUE`, `malloc()` and `g_malloc()` can be mixed.

### g_mem_profile ()

    void
    g_mem_profile (void);

`g_mem_profile` has been deprecated since version 2.46 and should not be used in newly-written code.

Use other memory profiling tools instead

GLib used to support some tools for memory profiling, but this no longer works. There are many other useful tools for memory profiling these days which can be used instead.

## Types and Values

### g_mem_gc_friendly

    extern gboolean g_mem_gc_friendly;

This variable is `TRUE` if the `G_DEBUG` environment variable includes the key `gc-friendly`.

### struct GMemVTable

    struct GMemVTable {
      gpointer (*malloc)      (gsize    n_bytes);
      gpointer (*realloc)     (gpointer mem,
    			   gsize    n_bytes);
      void     (*free)        (gpointer mem);
      /* optional; set to NULL if not used ! */
      gpointer (*calloc)      (gsize    n_blocks,
    			   gsize    n_block_bytes);
      gpointer (*try_malloc)  (gsize    n_bytes);
      gpointer (*try_realloc) (gpointer mem,
    			   gsize    n_bytes);
    };

A set of functions used to perform memory allocation. The same GMemVTable must be used for all allocations in the same program; a call to `g_mem_set_vtable()`, if it exists, should be prior to any use of GLib.

This functions related to this has been deprecated in 2.46, and no longer work.

#### Members

`malloc` () | function to use for allocating memory. |
`realloc` () | function to use for reallocating memory. |
`free` () | function to use to free memory. |
`calloc` () | function to use for allocating zero-filled memory. |
`try_malloc` () | function to use for allocating memory without a default error handler. |
`try_realloc` () | function to use for reallocating memory without a default error handler. |

### glib_mem_profiler_table

    extern GMemVTable *glib_mem_profiler_table;

`glib_mem_profiler_table` has been deprecated since version 2.46 and should not be used in newly-written code.

Use other memory profiling tools instead

Used to be a GMemVTable containing profiling variants of the memory allocation functions, but this variable shouldn't be modified anymore.