MALLOC(3F) — UNIX Programmer’s Manual

NAME

malloc, free, falloc − memory allocator

SYNOPSIS

subroutine malloc (size, addr)
integer size, addr

subroutine free (addr)
integer addr

subroutine falloc (nelem, elsize, clean, basevec, addr, offset)
integer nelem, elsize, clean, addr, offset

DESCRIPTION

Malloc, falloc and free provide a general-purpose memory allocation package. Malloc returns in addr the address of a block of at least size bytes beginning on an even-byte boundary.

Falloc allocates space for an array of nelem elements of size elsize and returns the address of the block in addr. It zeros the block if clean is 1. It returns in offset an index such that the storage may be addressed as basevec(offset+1) ... basevec(offset+nelem). Falloc gets extra bytes so that after address arithmetic, all the objects so addressed are within the block.

The argument to free is the address of a block previously allocated by malloc or falloc; this space is made available for further allocation, but its contents are left undisturbed. To free blocks allocated by falloc, use addr in calls to free, do not use basevec(offset+1).

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

DIAGNOSTICS

Malloc and falloc set addr to 0 if there is no available memory or if the arena has been detectably corrupted by storing outside the bounds of a block.

The following example shows how to obtain memory and use it within a subprogram:

       integer addr, work(1), offset
         ...
      call falloc ( n, 4, 0, work, addr, offset )
      do 10 i = 1, n
      work(offset+i) = ...
10    continue

The next example reads in dimension information, allocates space for two arrays and two vectors, and calls subroutine doit to do the computations:

       integer addr, dummy(1), offs
      read ∗, k, l, m
      indm1   = 1
      indm2   = indm1 + k∗l
      indm3   = indm2 + l∗m
      indsym = indm3 + k∗m
      lsym = n∗(n+1)/2
      indv = indsym + lsym
      indtot = indv + m
      call falloc ( indtot, 4, 0, dummy, addr, offs )
      call doit( dummy(indm1+offs), dummy(indm2+offs),
     .           dummy(indm3+offs), dummy(indsym+offs),
     .           dummy(indv +offs), m, n, lsym )
      end
      subroutine doit( arr1, arr2, arr3, vsym, vec, m, n, lsym )
      real arr1(k,l), arr2(l,m), arr3(k,m), vsym(lsym), v2(m)
         ...

FILES

/usr/lib/libU77.a

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