Not able to copy int array into struct address of given struct

Question

struct media{
     uint32_t addressOfPtr; 
 };

Some error somewhere, but I am not able to see it.

printf(" > %x",  ((uint8_t*) mediaObject2->addressOfPtr)[i]);

is not print

uint8_t message[SIZE_MAX];

for (i=0;i<SIZE_MAX;i++) {
    message[i] = i+1;
    printf(" > %x",  message[i]);
}

uint8_t *msg_Ptr;
msg_Ptr = malloc(SIZE_MAX*sizeof(uint8_t));
memcpy(msg_Ptr, &message, SIZE_MAX);

printf("\n####################\n");

for (i=0; i < SIZE_MAX; i++)  // message fixed at length 10
    printf(" > %x",  msg_Ptr[i]);

printf("\n");

struct media *mediaObject2;
(mediaObject2->addressOfPtr) = malloc(SIZE_MAX*sizeof(uint8_t));
(mediaObject2->addressOfPtr) = (uint32_t) msg_Ptr;
printf("\n####################\n"); // Last stop
//printf(">>>> %x ", mediaObject2->addressOfPtr);

printf("\n");
for (i=0; i < SIZE_MAX; i++)  // message fixed at length 10
    printf(" > %x",  ((uint8_t*) mediaObject2->addressOfPtr)[i]);

printf("\n");

And should use a different name SIZE_MAX from being used in <stdint.h>. — BLUEPIXY
– BLUEPIXY, Commented Jan 27, 2014 at 1:28

LihO · Accepted Answer · 2014-01-27 01:22:26Z

1

In this part:

struct media *mediaObject2;
(mediaObject2->addressOfPtr) = malloc(SIZE_MAX*sizeof(uint8_t));

you are using uninitialized pointer mediaObject2, which invokes an undefined behavior.

You need to either dynamically allocate memory for struct media or yet even better: use a variable with automatic storage duration here:

struct media mediaObject2;
mediaObject2.addressOfPtr = malloc(SIZE_MAX*sizeof(uint8_t));

Side note: If struct media was supposed to hold a pointer to an array of uint8_t, you should have declare this member as uint8_t *data or if the type is going to vary but it will be a pointer still, then void* dataPtr at least... anything is better than uint32_t addressOfPtr;.

answered Jan 27, 2014 at 1:22

LihO

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3 Comments

Ursa Major Over a year ago

excellent. @LihO. On a further question. how do I pass it to a function, say: void functionB (void* mediaObject) and pass the struct back to uint8_t message[SIZE_MAX]?

LihO Over a year ago

@UrsaMajor: functionB(&mediaObject2)... you might consider spending more time reading some books or other relevant materials.

Ursa Major Over a year ago

I did that, but it is not able to reload within the function to the uint8_t message[].

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