Make an array of arrays of strings

Question

I have arrays of strings. I want to put these arrays into an array. How can I do so? I have tried this:

char const * const fruits[3] = {
    "apple",
    "banana",
    "orange",
};

char const * const colors[3] = {
    "red",
    "green",
    "blue",
};

char * preset_configurations[3] =
{
    NULL, /* leave the first one blank so that this list is 1-based */
    &fruits,
    &colors,
};

but I get warning: initialization from incompatible pointer type. Any idea?

Don't put the ampersand in front of fruits and colors. Since they are arrays, they will be interpreted as pointers to their first elements in that situation. — ooga, Jan 31 '14 at 23:27

ooga · Accepted Answer · 2014-02-01T00:06:45.453

3

You need a double pointer and some consts (as well as getting rid of the ampersands) :

char const * const * preset_configurations[3] =
{
    NULL, /* leave the first one blank so that this list is 1-based */
    fruits,
    colors
};

EDIT: I suppose, given the extra information after I posted the above, that the best solution to your problem is:

// This will copy the characters of the words into the 3 16-byte arrays.
char fruits[3][16] = {
    "apple",
    "banana",
    "orange"
};
// Ditto.
char colors[3][16] = {
    "red",
    "green",
    "blue"
};
// This is how to point to the above.
char (*preset_configurations[3])[16] = {
    NULL, // this list is 1-based
    fruits,
    colors,
};

That way the strings are no longer constant strings (which, as you said, the exec functions don't want).

edited Feb 01 '14 at 00:06

answered Jan 31 '14 at 23:30

ooga

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const preservation FTW! – ooga Jan 31 '14 at 23:31
Is it possible for me to have `preset_configurations` be a `char * const*`? I am trying to pass it to the linux `execv` function which requires `char * const*`. – boltup_im_coding Jan 31 '14 at 23:33
Just remove the first const from all of them. Although, technically, you should have `char const` since you're pointing to string constants. – ooga Jan 31 '14 at 23:34
@ooga note, that will flag at least a compiler warning for deprecation since the literal is const by nature. Most C-compilers will allow it regardless unless some pretty pedantic warnings are being used. Ex: clang will report: "Initializing `'char *const *'` with an expression of type `'const char *const [3]'` discards qualifiers in nested pointer types." – WhozCraig Jan 31 '14 at 23:37
Right, I should have said "use actual char arrays and initialize them with your strings". – ooga Jan 31 '14 at 23:40
Hmmm.. I think I got it. I had the const's that way because of my question here: http://stackoverflow.com/questions/21491713/array-element-is-a-variable-in-array-of-strings-in-c/21491928 – boltup_im_coding Jan 31 '14 at 23:40
Can you explain a little about what's going on? I am new to C and hate asking these dumb questions. I would like to understand better `const * const *` and arrays, etc... – boltup_im_coding Jan 31 '14 at 23:41
1

@unexpected62 ensconced within [this answer to a somewhat related question](http://stackoverflow.com/questions/14562845/why-does-passing-char-as-const-char-generate-a-warning/14566215#14566215) is a diatribe on every conceivable meaning of `const` and `*` through double-indirection (i.e. pointers to pointers). It may help you understand better. – WhozCraig Jan 31 '14 at 23:43

score 0 · Answer 2 · answered Feb 01 '14 at 00:22

0

typedef const char const *(*cp3)[3];
cp3 preset_configurations[3] = {
    NULL,
    &fruits,
    &colors,
};
//printf("%s\n", (*preset_configurations[1])[2]);//orange

answered Feb 01 '14 at 00:22

BLUEPIXY

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Make an array of arrays of strings

2 Answers2