Matrix Elements VB-800 Manuel d'utilisateur télécharger pdf (Page 14)

6 Appendix A1 Extending Ox

A1.2.3 Dynamic link library and search paths

Note that the operating system has to be able to ﬁnd the DLL ﬁle. In the example above

we gave the partial path, assuming the Ox ﬁle is run from its current location.

When making a package for distribution, the proper location is the ox/packages

folder. By default, Ox will search relative to ox/include and then to ox. More for-

mally, if the speciﬁed DLL name in the extern statement contains a relative path, Ox

will search in

(1) in the folder of the source ﬁle;

(2) along the OX3PATH environment variable;

If this is not deﬁned under Windows a default path will be derived from the loca-

tion of oxwin.dll.

(3) along folders speciﬁed in the import statement;

(4) if the library name does not contain a path at all, say it is xlib, then it will try

packages/xlib/xlib using the appropriate extension.

Alternatively you could add your own directory to the OX3PATH environment vari-

able, or use the #import statement.

A1.3 Adding C/C

code: returning values in arguments

Returning a value in an argument only adds a minor complication. Remember that by

default all arguments in Ox and C are passed by value, and assignments to arguments

will be lost after the function returns. To return values in arguments, pass a pointer to a

variable, so that the called function may change what the variable points to.

To refresh our memory, here is some simple Ox code:

#include <oxstd.h>

func1(a)

{a=1;

}

func2(const a)

{ a[0] = 1;

}

main()

{

decl b;

b = 0; func1(b); print(b);

b = 0; func2(&b); print(b);

}

This will print 01.Infunc1 we cannot use the const qualiﬁer because we are changing

the argument. In func2 the argument is not changed, only what it points to.

The ﬁrst serious example is the invert function from the standard library, which

also illustrates the use of a variable argument list.

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Matrix Elements VB-800 Manuel d'utilisateur Page 14