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   Programming a BEA Tuxedo Application Using FML

The only restriction on the location of fielded buffers is that they must be aligned on a short boundary. Otherwise, fielded buffers are position-independent and may be moved around freely in memory.

If src points to a fielded buffer and dest points to an area of storage big enough to hold it, then the following code might be used to move the fielded buffer.

FBFR *src;
char *dest;
. . .
memcpy(dest, src, Fsizeof(src));

The function memcpy, one of the C run-time memory management functions, moves the number of bytes indicated by its third argument from the area pointed to by its second argument to the area pointed to by its first argument.

While memcpy may be used to copy a fielded buffer, the destination copy of the buffer looks just like the source copy. In particular, for example, the destination copy has the same number of unused bytes as the source buffer.

Fmove acts like memcpy, but does not need an explicit length (which is computed).

int
Fmove(char *dest, FBFR *src)

Here:

• dest is a pointer to the destination buffer.

• src is a pointer to the source fielded buffer.

In the following code, for example, Fmove checks that the source buffer is indeed a fielded buffer, but does not modify the source buffer in any way.

The destination buffer need not be a fielded buffer (that is, it need not have been allocated using Falloc), but it must be aligned on a short boundary (4-byte alignment for FML32). Thus, Fmove provides an alternative to Fcpy when you want to copy a fielded buffer to a non-fielded buffer. Fmove does not, however, check to make sure there is enough room in the destination buffer to receive the source buffer.

For values of type FLD_PTR, Fmove32 transfers the buffer pointer. The application programmer must manage the reallocation and freeing of buffers when the associated pointer is moved. The buffer pointed to by a FLD_PTR field must be allocated using the tpalloc(3c) call.

For more information, refer to Fmove, Fmove32(3fml) in the BEA Tuxedo FML Function Reference.

Fcpy is used to overwrite one fielded buffer with another.

int
Fcpy(FBFR *dest, FBFR *src)

Here:

• dest is a pointer to the destination fielded buffer.

• src is a pointer to the source fielded buffer.

Fcpy preserves the overall buffer length of the overwritten fielded buffer and therefore is useful for expanding or reducing the size of a fielded buffer. Consider the following example.

Unlike Fmove, where dest could point to an uninitialized area, Fcpy expects dest to point to an initialized fielded buffer (allocated using Falloc). Fcpy also verifies that dest is big enough to accommodate the data from the source buffer.

Note: You cannot reduce the size of a fielded buffer below the amount of space needed for currently held data.

As with Fmove, the source buffer is not modified by Fcpy.

For values of type FLD_PTR, Fcpy32 copies the buffer pointer. The application programmer must manage the reallocation and freeing of buffers when the associated pointer is copied. The buffer pointed to by a FLD_PTR field must be allocated using the tpalloc(3c) call.

For more information, refer to Fcpy, Fcpy32(3fml) in the BEA Tuxedo FML Function Reference.