Matrix Elements VB-800 Manuel d'utilisateur télécharger pdf (Page 11)

A1.2 Adding C/C

code: a simple dynamic link library 3

• All functions have the same format:

– OXCALL deﬁnes the calling convention;

– rtn is the return value of the function. It is a pointer to an OxVALUE which

is the container for any Ox variable. On input, it is an integer (OX

INT)of

value 0. If the function returns a value, it should be stored in rtn.

– pv is an array of cArg OxVALUEs, holding the actual arguments to the func-

tion.

– cArg is the number of arguments used in the function call. Unless the func-

tion has a variable number of arguments, there is no need to reference this

value.

• If the function is written in C

instead of C, it must be declared as:

extern "C" void OXCALL FnThrees

(OxVALUE *rtn, OxVALUE *pv, int cArg)

• First, we check whether the arguments are of type OX INT (we know that there are

two arguments, which have index 0 and 1 in pv). The call to OxLibCheckType

tests pv (the function arguments) from index 0 to index 1 for type OX

INT.

Arguments must be checked for type before being accessed. Make

sure there is a call to OxLibCheckType for each argument (unless

you inspect the arguments ‘manually’).

In this case, a double would also be valid, but automatically converted to an

integer by the OxLibCheckType function. Any other argument type would result

in a run-time error (checking for the number of arguments is done at compile

time).

• For convenience, we copy the ﬁrst argument to r, and the second to c. OxInt

accesses the integer in an OxVALUE. The ﬁrst argument is the array of OxVALUEs,

the second argument is the index in the array. This speciﬁes the dimension of the

requested matrix.

• The return type is a matrix, and that matrix has to be allocated in the rtn value,

using the right dimensions. This is done with the OxLibValMatMalloc function.

A run-time error is generated if there is not enough memory to allocate the matrix.

• Finally we have to set all elements of the matrix to the value 3. OxMat accesses

the allocated matrix. The dimensions of that matrix are accessed by OxMatc,

OxMatr, but here we already know the dimensions.

Note that the function arguments, as contained in pv, may only be changed if they

are declared as const. It is best to never change the arguments in the function,ex-

cept from conversion from int to double and vice versa (automatic conversion using

OxLibCheckType is always safe). Another exception is when the argument is a pointer

in which the caller expects a return value. An example will follow shortly.

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Matrix Elements VB-800 Manuel d'utilisateur Page 11

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