Heap Management

Functions responsible for allocating, freeing, and copying memory. More...

Functions
void *	av_malloc (size_t size) av_malloc_attrib
	Allocate a memory block with alignment suitable for all memory accesses (including vectors if available on the CPU). More...
void *	av_mallocz (size_t size) av_malloc_attrib
	Allocate a memory block with alignment suitable for all memory accesses (including vectors if available on the CPU) and zero all the bytes of the block. More...
void *	av_malloc_array (size_t nmemb, size_t size)
	Allocate a memory block for an array with av_malloc(). More...
void *	av_mallocz_array (size_t nmemb, size_t size)
	Allocate a memory block for an array with av_mallocz(). More...
void *	av_calloc (size_t nmemb, size_t size) av_malloc_attrib
	Non-inlined equivalent of av_mallocz_array(). More...
void *	av_realloc (void *ptr, size_t size)
	Allocate, reallocate, or free a block of memory. More...
av_warn_unused_result int	av_reallocp (void *ptr, size_t size)
	Allocate, reallocate, or free a block of memory through a pointer to a pointer. More...
void *	av_realloc_f (void *ptr, size_t nelem, size_t elsize)
	Allocate, reallocate, or free a block of memory. More...
void *	av_realloc_array (void *ptr, size_t nmemb, size_t size)
	Allocate, reallocate, or free an array. More...
int	av_reallocp_array (void *ptr, size_t nmemb, size_t size)
	Allocate, reallocate, or free an array through a pointer to a pointer. More...
void *	av_fast_realloc (void *ptr, unsigned int *size, size_t min_size)
	Reallocate the given buffer if it is not large enough, otherwise do nothing. More...
void	av_fast_malloc (void *ptr, unsigned int *size, size_t min_size)
	Allocate a buffer, reusing the given one if large enough. More...
void	av_fast_mallocz (void *ptr, unsigned int *size, size_t min_size)
	Allocate and clear a buffer, reusing the given one if large enough. More...
void	av_free (void *ptr)
	Free a memory block which has been allocated with a function of av_malloc() or av_realloc() family. More...
void	av_freep (void *ptr)
	Free a memory block which has been allocated with a function of av_malloc() or av_realloc() family, and set the pointer pointing to it to NULL. More...
char *	av_strdup (const char *s) av_malloc_attrib
	Duplicate a string. More...
char *	av_strndup (const char *s, size_t len) av_malloc_attrib
	Duplicate a substring of a string. More...
void *	av_memdup (const void *p, size_t size)
	Duplicate a buffer with av_malloc(). More...
void	av_memcpy_backptr (uint8_t *dst, int back, int cnt)
	Overlapping memcpy() implementation. More...

Detailed Description

Functions responsible for allocating, freeing, and copying memory.

All memory allocation functions have a built-in upper limit of INT_MAX bytes. This may be changed with av_max_alloc(), although exercise extreme caution when doing so.

Function Documentation

av_malloc()

void* av_malloc

(

size_t

size

)

Allocate a memory block with alignment suitable for all memory accesses (including vectors if available on the CPU).

Parameters

size	Size in bytes for the memory block to be allocated

Returns

Pointer to the allocated block, or NULL if the block cannot be allocated

See also

av_mallocz()

Examples:

avio_reading.c, and hw_decode.c.

Referenced by decode_write(), and main().

av_mallocz()

void* av_mallocz

(

size_t

size

)

Allocate a memory block with alignment suitable for all memory accesses (including vectors if available on the CPU) and zero all the bytes of the block.

Parameters

size	Size in bytes for the memory block to be allocated

Returns

Pointer to the allocated block, or NULL if it cannot be allocated

See also

av_malloc()

av_malloc_array()

void* av_malloc_array	(	size_t	nmemb,
		size_t	size
	)

Allocate a memory block for an array with av_malloc().

The allocated memory will have size size * nmemb bytes.

Parameters

nmemb	Number of element
size	Size of a single element

Returns

Pointer to the allocated block, or NULL if the block cannot be allocated

See also

av_malloc()

Examples:

transcoding.c.

Referenced by init_filters().

av_mallocz_array()

void* av_mallocz_array	(	size_t	nmemb,
		size_t	size
	)

Allocate a memory block for an array with av_mallocz().

The allocated memory will have size size * nmemb bytes.

Parameters

nmemb	Number of elements
size	Size of the single element

Returns

Pointer to the allocated block, or NULL if the block cannot be allocated

See also

av_mallocz()

av_malloc_array()

Examples:

remuxing.c, and transcoding.c.

Referenced by main(), and open_input_file().

av_calloc()

void* av_calloc	(	size_t	nmemb,
		size_t	size
	)

Non-inlined equivalent of av_mallocz_array().

Created for symmetry with the calloc() C function.

av_realloc()

void* av_realloc	(	void *	ptr,
		size_t	size
	)

Allocate, reallocate, or free a block of memory.

If ptr is NULL and size > 0, allocate a new block. If size is zero, free the memory block pointed to by ptr. Otherwise, expand or shrink that block of memory according to size.

Parameters

ptr	Pointer to a memory block already allocated with av_realloc() or NULL
size	Size in bytes of the memory block to be allocated or reallocated

Returns

Pointer to a newly-reallocated block or NULL if the block cannot be reallocated or the function is used to free the memory block

Warning

Unlike av_malloc(), the returned pointer is not guaranteed to be correctly aligned.

See also

av_fast_realloc()

av_reallocp()

av_reallocp()

av_warn_unused_result int av_reallocp	(	void *	ptr,
		size_t	size
	)

Allocate, reallocate, or free a block of memory through a pointer to a pointer.

If *ptr is NULL and size > 0, allocate a new block. If size is zero, free the memory block pointed to by *ptr. Otherwise, expand or shrink that block of memory according to size.

Parameters

[in,out]	ptr	Pointer to a pointer to a memory block already allocated with av_realloc(), or a pointer to NULL. The pointer is updated on success, or freed on failure.
[in]	size	Size in bytes for the memory block to be allocated or reallocated

Returns

Zero on success, an AVERROR error code on failure

Warning

Unlike av_malloc(), the allocated memory is not guaranteed to be correctly aligned.

av_realloc_f()

void* av_realloc_f	(	void *	ptr,
		size_t	nelem,
		size_t	elsize
	)

Allocate, reallocate, or free a block of memory.

This function does the same thing as av_realloc(), except:

• It takes two size arguments and allocates nelem * elsize bytes, after checking the result of the multiplication for integer overflow.
• It frees the input block in case of failure, thus avoiding the memory leak with the classic

  buf = realloc(buf);
  if (!buf)
      return -1;

  pattern.

av_realloc_array()

void* av_realloc_array	(	void *	ptr,
		size_t	nmemb,
		size_t	size
	)

Allocate, reallocate, or free an array.

If ptr is NULL and nmemb > 0, allocate a new block. If nmemb is zero, free the memory block pointed to by ptr.

Parameters

ptr	Pointer to a memory block already allocated with av_realloc() or NULL
nmemb	Number of elements in the array
size	Size of the single element of the array

Returns

Pointer to a newly-reallocated block or NULL if the block cannot be reallocated or the function is used to free the memory block

Warning

Unlike av_malloc(), the allocated memory is not guaranteed to be correctly aligned.

See also

av_reallocp_array()

av_reallocp_array()

int av_reallocp_array	(	void *	ptr,
		size_t	nmemb,
		size_t	size
	)

Allocate, reallocate, or free an array through a pointer to a pointer.

If *ptr is NULL and nmemb > 0, allocate a new block. If nmemb is zero, free the memory block pointed to by *ptr.

Parameters

[in,out]	ptr	Pointer to a pointer to a memory block already allocated with av_realloc(), or a pointer to NULL. The pointer is updated on success, or freed on failure.
[in]	nmemb	Number of elements
[in]	size	Size of the single element

Returns

Zero on success, an AVERROR error code on failure

Warning

Unlike av_malloc(), the allocated memory is not guaranteed to be correctly aligned.

av_fast_realloc()

void* av_fast_realloc	(	void *	ptr,
		unsigned int *	size,
		size_t	min_size
	)

Reallocate the given buffer if it is not large enough, otherwise do nothing.

If the given buffer is NULL, then a new uninitialized buffer is allocated.

If the given buffer is not large enough, and reallocation fails, NULL is returned and *size is set to 0, but the original buffer is not changed or freed.

A typical use pattern follows:

uint8_t *buf = ...;
uint8_t *new_buf = av_fast_realloc(buf, &current_size, size_needed);
if (!new_buf) {
    // Allocation failed; clean up original buffer
    av_freep(&buf);
    return AVERROR(ENOMEM);
}

Parameters

[in,out]	ptr	Already allocated buffer, or NULL
[in,out]	size	Pointer to the size of buffer ptr. *size is updated to the new allocated size, in particular 0 in case of failure.
[in]	min_size	Desired minimal size of buffer ptr

Returns

ptr if the buffer is large enough, a pointer to newly reallocated buffer if the buffer was not large enough, or NULL in case of error

See also

av_realloc()

av_fast_malloc()

av_fast_malloc()

void av_fast_malloc	(	void *	ptr,
		unsigned int *	size,
		size_t	min_size
	)

Allocate a buffer, reusing the given one if large enough.

Contrary to av_fast_realloc(), the current buffer contents might not be preserved and on error the old buffer is freed, thus no special handling to avoid memleaks is necessary.

*ptr is allowed to be NULL, in which case allocation always happens if size_needed is greater than 0.

uint8_t *buf = ...;
av_fast_malloc(&buf, &current_size, size_needed);
if (!buf) {
    // Allocation failed; buf already freed
    return AVERROR(ENOMEM);
}

Parameters

[in,out]	ptr	Pointer to pointer to an already allocated buffer. *ptr will be overwritten with pointer to new buffer on success or NULL on failure
[in,out]	size	Pointer to the size of buffer *ptr. *size is updated to the new allocated size, in particular 0 in case of failure.
[in]	min_size	Desired minimal size of buffer *ptr

See also

av_realloc()

av_fast_mallocz()

av_fast_mallocz()

void av_fast_mallocz	(	void *	ptr,
		unsigned int *	size,
		size_t	min_size
	)

Allocate and clear a buffer, reusing the given one if large enough.

Like av_fast_malloc(), but all newly allocated space is initially cleared. Reused buffer is not cleared.

*ptr is allowed to be NULL, in which case allocation always happens if size_needed is greater than 0.

Parameters

[in,out]	ptr	Pointer to pointer to an already allocated buffer. *ptr will be overwritten with pointer to new buffer on success or NULL on failure
[in,out]	size	Pointer to the size of buffer *ptr. *size is updated to the new allocated size, in particular 0 in case of failure.
[in]	min_size	Desired minimal size of buffer *ptr

See also

av_fast_malloc()

av_free()

void av_free

(

void *

ptr

)

Free a memory block which has been allocated with a function of av_malloc() or av_realloc() family.

Parameters

ptr	Pointer to the memory block which should be freed.

Note

ptr = NULL is explicitly allowed.

It is recommended that you use av_freep() instead, to prevent leaving behind dangling pointers.

See also

av_freep()

Examples:

decode_audio.c, demuxing_decoding.c, and transcoding.c.

Referenced by main().

av_freep()

void av_freep

(

void *

ptr

)

Free a memory block which has been allocated with a function of av_malloc() or av_realloc() family, and set the pointer pointing to it to NULL.

uint8_t *buf = av_malloc(16);
av_free(buf);
// buf now contains a dangling pointer to freed memory, and accidental
// dereference of buf will result in a use-after-free, which may be a
// security risk.

uint8_t *buf = av_malloc(16);
av_freep(&buf);
// buf is now NULL, and accidental dereference will only result in a
// NULL-pointer dereference.

Parameters

ptr	Pointer to the pointer to the memory block which should be freed

Note

*ptr = NULL is safe and leads to no action.

See also

av_free()

Examples:

avio_reading.c, filter_audio.c, http_multiclient.c, hw_decode.c, remuxing.c, resampling_audio.c, scaling_video.c, and transcode_aac.c.

Referenced by decode_write(), init_converted_samples(), main(), process_client(), and read_decode_convert_and_store().

av_strdup()

char* av_strdup

(

const char *

s

)

Duplicate a string.

Parameters

s	String to be duplicated

Returns

Pointer to a newly-allocated string containing a copy of s or NULL if the string cannot be allocated

See also

av_strndup()

Examples:

filtering_audio.c, filtering_video.c, transcode_aac.c, and transcoding.c.

Referenced by init_filter(), init_filters(), and open_output_file().

av_strndup()

char* av_strndup	(	const char *	s,
		size_t	len
	)

Duplicate a substring of a string.

Parameters

s	String to be duplicated
len	Maximum length of the resulting string (not counting the terminating byte)

Returns

Pointer to a newly-allocated string containing a substring of s or NULL if the string cannot be allocated

av_memdup()

void* av_memdup	(	const void *	p,
		size_t	size
	)

Duplicate a buffer with av_malloc().

Parameters

p	Buffer to be duplicated
size	Size in bytes of the buffer copied

Returns

Pointer to a newly allocated buffer containing a copy of p or NULL if the buffer cannot be allocated

av_memcpy_backptr()

void av_memcpy_backptr	(	uint8_t *	dst,
		int	back,
		int	cnt
	)

Overlapping memcpy() implementation.

Parameters

dst	Destination buffer
back	Number of bytes back to start copying (i.e. the initial size of the overlapping window); must be > 0
cnt	Number of bytes to copy; must be >= 0

Note

cnt > back is valid, this will copy the bytes we just copied, thus creating a repeating pattern with a period length of back.