Re: Macro question

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Wed, 30 May 2007 15:30:22 -0400

Message-ID:

<f3kjch$7sj$1@news.datemas.de>

Peithon wrote:

[..]
I'm creating an array of unit test structures to input into a search
function.

It searches for 'key' amongst the strings contained in 'arr'. Now the
number of strings contained in arr needs to vary from test to test.

So I might have 5 strings in my first ut struct but 26 in the next.

So I thought I'd create 20 tests with a huge upper limit, say 100, as
in

Code:

typedef struct
{
char * key;
char * arr[100];
}unit_test[20];

Anonymous structs are really to be avoided in C++. Give it a name,
you'll find that it's better that way...

    struct UnitTest {
        char const* key;
        char const* arr[100];
    };

    UnitTest unit_test[20];

But any initialisation arrays of less than a 100 strings will leave
uninitialised ptrs, e.g.

Code:

typedef struct
{
char * key;
char * arr[100];
}unit_test[20] = {
{ "three", { "five", "four", "one", "three", "two" } }, //test1
leaves 95 bad ptrs

Actually, not "bad ptrs". _Null_ ptrs.

.....,
....,
{ "two", { "five", "four", "one"} } //test20 leaves 97 bad ptrs

Again, not "bad ptrs".

};

So I thought I'd declare

Code:

typedef struct
{
char * key;
char * arr[100];
}unit_test[20];

globally to get all the ptrs nulled for free and then initialise
within a for loop.

You should get them "for free" if you have fewer initialisers than
elements of the array.

Using the structures

Code:

unit_test UT1 = { "three", { "five", "four", "one", "three",
"two" } };
...
unit_test UT20 = { "two", { "five", "four", "one" } };
Then, the question became how do you reference names UT1, UT2,...,UT20
within a for loop. Answer, macro! Or apparently not because it's
compile-time and I need things init'd at run-time.

How would you achieve the desired result?

Don't do anything special. If your compiler doesn't create null
pointers for the omitted elements of the array, complain to the
compiler vendor/manufacturer.

    struct UnitTest {
        char const* key;
        char const* arr[100];
    };
    #include <cassert>
    int main() {
        UnitTest unit_test[20] = { { "one", { "one", "two", "three" } },
                         { "zwei", { "eins", "zwei", "drei", "vier" } },
                   { "pet", { "jedna", "dve", "tri", "ctyri", "pet" } } };
        assert(unit_test[0].arr[3] == 0);
        assert(unit_test[0].arr[99] == 0);
        assert(unit_test[3].key == 0);
    }

V
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