CODEWITHSUNDEEP
c
Avinash
Avinash

Reputation: 13257

how do I initialize structure containing pointer to pointer

following is the structure and I want to create array of this structure in C and initialize, but confuse with how to initialize char **input and char **output.

typedef struct _test_data_vector {
    char *api;
    char **input;
    char **output;
}vector_test_data;

following is what I tried.

typedef struct _test_data_vector {
    char *api;
    char **input;
    char **output;
}vector_test_data;

vector_test_data data[] = {
    {
        "vector_push_back",
        {"1","2","3","4","5","6","7","8","9","10"},
        {"1","2","3","4","5","6","7","8","9","10"}
    }
};

Upvotes: 1

Views: 2521

Answers (4)

Martin Babacaev
Martin Babacaev

Reputation: 6280

You're very close, just specify type through compound literals (starting from C99)

This what I've tested with no warnings:

typedef struct _test_data_vector {
    char *api;
    char **input;
    char **output;
}vector_test_data;

vector_test_data data[] = {
    {
        "vector_push_back",
        (char*[]){"1","2","3","4","5","6","7","8","9","10"},
        (char*[]){"1","2","3","4","5","6","7","8","9","10"}
    }
};

printf("TEST: %s", data[0].input[2]);

Otput: TEST: 3

Upvotes: 1

William Pursell
William Pursell

Reputation: 212178

char text[] = "Input text";
char *output;
struct _test_data_vector {
    char *api;
    char **input;
    char **output;
};

struct _test_data_vector A = { NULL, &text, &output };

If you want to allocate space for them, you can also do:

struct _test_data_vector B = {
  "api",
  malloc( 5 * sizeof *B.input ),
  malloc( 10 * sizeof *B.output )
};

just make sure you check that the allocation was succesful. (I strongly advised against doing this, as it is much clearer to call malloc in non-initializer code.)

Upvotes: 0

Jim Balter
Jim Balter

Reputation: 16406

api, input, and output will, by default, be initialized to NULL. You can initialize api directly, but input and output must be allocated, either at compile time by defining arrays, or at runtime, perhaps via malloc. You really should provide more information about what you are trying to do in order to get a more helpful answer.

Upvotes: 0

Radu
Radu

Reputation: 3494

be a little more specific , usually when you have to initialize a pointer to a pointer you do it like this:

char * charPointer;//this is the char you want the input to point at;
*input = charPointer;

I had to use pointer to pointer on a project to but if ther is any way you can avoid this it would be easyer

Upvotes: 0

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