Question

I am new to C and have a question about initializing a structure. I am using a structure that I have not created and so I don’t know what is inside of it. Therefore, I did not initialize it but the compiler complained. So I set it equal to NULL but I got a segmentation fault. Then I looked up how to set everything to 0 and it said to set it equal to {0}. That too gave me a segmentation fault. Since I know the function I am calling is correct, and that the array I pass it is of the correct size, I am almost certain it has something to do with the way I initialize the structure. The initialization is

struct aes_ctx *aes_struct = {0}

The header for the function is

void aes_setkey(aes_ctx *aes, const void *key, u_int len);

The way that I am calling it is

aes_setkey(aes_struct, aes, CCA_STRENGTH);

where aes is a buffer of size 16, CCA_STRENGTH is a constant int of 16.

To sum up the problem, I think that the way that I initialize the structure causes it to be unusable later on. Any help that can be given to me on this would be so appreciated!
Thanks!

Answer 1

You cannot initialize a pointer that way (well, you can, it just doesn’t point to anythign valid). Something like this is what you are after:

struct aes_ctx aes_struct = {0};

You can then pass the address of aes_struct to the function, but that depends on whether or not you need to dynamically allocate this thing (required scope and the size of the type will dictate this).

So…

struct aes_ctx aes_struct = {0};
aes_setkey(&aes_struct, aes, CCA_STRENGTH);

Or

struct aes_ctx *aes_struct = malloc(sizeof(struct aes_ctx));
/* you may want to initialize the structure via memset or some init function */
aes_setkey(aes_struct, aes, CCA_STRENGTH);