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MathGroup Archive 2008

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C++ const and mathlink

  • To: mathgroup at smc.vnet.net
  • Subject: [mg85667] C++ const and mathlink
  • From: Art <grenander at gmail.com>
  • Date: Tue, 19 Feb 2008 01:49:19 -0500 (EST)

I am writing mathlink wrappers for a C++ library on 6.0.1, Linux
x86-64. I have a single .tm with no C++ code and a .cpp file. I am
confused about the usage of const in several places:

1. Functions such as MLPutReal64List and MLEvaluate don't have const
arguments. Is there any way to change their declaration through a
define such as MLCONST in mathlink.h so that they are more const
friendly.  It seems like most of mathlink functions have const's in
the declarations. I am wondering why these don't. Do they change their
arguments? Is it safe to const_cast<>? The practical cost is that I
have to instantiate array copies before returning them.

2. Can mprep generate declarations that have const's when using C++?
If I define functions with const variables in my .cpp file, then I get
link errors as the mprep generated declarations don't match. I've
tried variations of mprep -prototypes (default on my system) and
noprototypes, declaring my functions in the .tm file with consts like
in the reverse.tm example, with no luck.

Also, mprep leads to linker errors unless I set CC=g++.

What is the correct way? The documentation and examples are very C
friendly but not so much for C++.

- Art


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