Re: Comparing a Vector with Another Vector or a Single Value

From:

Alberto Ganesh Barbati <AlbertoBarbati@libero.it>

Newsgroups:

comp.lang.c++.moderated

Date:

Fri, 28 Dec 2007 09:46:29 CST

Message-ID:

<nFLcj.207347$U01.1362129@twister1.libero.it>

Charles ha scritto:

Consider a function that compares a vector of doubles, for instance, with
either another vector of equal length or just a single double. The type of
comparison is not known until runtime. The output will be a vector of
bools.

Case 1:
For each element in vectorA, if vectorA[x] is greater than vectorB[x],
output[x] = true. Otherwise output[x] = false.
Case 2:
For each element in vectorA, if vectorA[x] is greater than doubleB,
output[x] = true. Otherwise output[x] = false.

My plan is to use a Boost:Variant to hold either a pointer to vectorB or
doubleB itself. The comparison function will step through vectorA and
either
compare each element with the corresponding element in vectorB or just the
single doubleB value. (I could also just fill a vector with multiple
copies
of doubleB, eliminating Case 2 above.)

Is this the best approach?

That approach looks like it has been borrowed from some scripted
language without strict type checking and overloading. Definitely, it is
*not* the best approach in C++. Just write two functions:

void compare(const std::vector<double>& valuesA,
             const std::vector<double>& valuesB,
             std::vector<bool>& results);

void compare(const std::vector<double>& valuesA,
             double valueB,
             std::vector<bool>& results);

and let the compiler decide statically which is the right function to
call according the type of the arguments. As a rule of thumb, you should
avoid boost.variant for these simple tasks.

HTH,

Ganesh

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