MALLOC(3)                                                            MALLOC(3)



NAME
       malloc, free, realloc, calloc, alloca - memory allocator

SYNOPSIS
       char *malloc(size)
       unsigned size;

       free(ptr)
       char *ptr;

       char *realloc(ptr, size)
       char *ptr;
       unsigned size;

       char *calloc(nelem, elsize)
       unsigned nelem, elsize;

       char *alloca(size)
       int size;

DESCRIPTION
       _M_a_l_l_o_c  and  _f_r_e_e  provide a general-purpose memory allocation package.
       _M_a_l_l_o_c returns a pointer to a block of at least _s_i_z_e bytes beginning on
       a word boundary.

       The  argument  to  _f_r_e_e is a pointer to a block previously allocated by
       _m_a_l_l_o_c; this space is made available for further  allocation,  but  its
       contents are left undisturbed.

       Needless  to  say,  grave disorder will result if the space assigned by
       _m_a_l_l_o_c is overrun or if some random number is handed to _f_r_e_e.

       _M_a_l_l_o_c maintains multiple lists of free blocks according to size, allo‐
       cating  space from the appropriate list.  It calls _s_b_r_k (see _b_r_k(2)) to
       get more memory from the system when there is no suitable space already
       free.

       _R_e_a_l_l_o_c  changes  the size of the block pointed to by _p_t_r to _s_i_z_e bytes
       and returns a pointer to the (possibly moved) block.  The contents will
       be unchanged up to the lesser of the new and old sizes.

       In  order  to  be compatible with older versions, _r_e_a_l_l_o_c also works if
       _p_t_r points to a block freed since the last call of _m_a_l_l_o_c_,  _r_e_a_l_l_o_c  or
       _c_a_l_l_o_c;  sequences  of _f_r_e_e_, _m_a_l_l_o_c and _r_e_a_l_l_o_c were previously used to
       attempt storage compaction.  This procedure is no longer recommended.

       _C_a_l_l_o_c allocates space for an array of _n_e_l_e_m elements of  size  _e_l_s_i_z_e_.
       The space is initialized to zeros.

       _A_l_l_o_c_a  allocates _s_i_z_e bytes of space in the stack frame of the caller.
       This temporary space is automatically freed on return.

       Each of the allocation routines returns a  pointer  to  space  suitably
       aligned  (after  possible  pointer coercion) for storage of any type of
       object.  If the space is of _p_a_g_e_s_i_z_e or  larger,  the  memory  returned
       will be page-aligned.

SEE ALSO
       brk(2), pagesize(2)

DIAGNOSTICS
       _M_a_l_l_o_c_,  _r_e_a_l_l_o_c  and  _c_a_l_l_o_c  return a null pointer (0) if there is no
       available memory or if the  arena  has  been  detectably  corrupted  by
       storing  outside  the  bounds  of a block.  _M_a_l_l_o_c may be recompiled to
       check the arena very stringently on every transaction; those sites with
       a  source code license may check the source code to see how this can be
       done.

BUGS
       When _r_e_a_l_l_o_c returns 0, the block pointed to by _p_t_r may be destroyed.

       The current implementation of _m_a_l_l_o_c does not  always  fail  gracefully
       when system memory limits are approached.  It may fail to allocate mem‐
       ory when larger free blocks could be broken  up,  or  when  limits  are
       exceeded  because  the  size  is rounded up.  It is optimized for sizes
       that are powers of two.

       _A_l_l_o_c_a is machine dependent; its use is discouraged.



4th Berkeley Distribution        May 14, 1986                        MALLOC(3)