Incomplete copy from struct to array

Question

I have defined:

 #define arrayLengthInStruct 50

 typedef struct {
  struct {
        int _buf[arrayLengthInStruct];           
        int _bufLen;
 } _context;
} _handle;

in main()

_handle handlePtr;
_handle* handle = (_handle*) &handlePtr;   // data is here
int* k_src = NULL; // to be loaded to
int i = 0;

handlePtr._context._bufLen = arrayLengthInStruct;
// initialize the source
for (i = 0; i < handlePtr._context._bufLen; i++) {
    handlePtr._context._buf[i] = i+1;
    printf("%d \t", handlePtr._context._buf[i]);
}
printf("\n");

k_src = malloc(sizeof(int)*(handlePtr._context._bufLen)); 
printf("Amount of data to copy: %d \n", handle->_context._bufLen);   


  memcpy ( k_src,
  &handle->_context._buf[0],
   handle->_context._bufLen
 );

for (i = 0; i < handlePtr._context._bufLen; i++) {
    printf("%d \t", k_src[i]);
}
printf("\n");

However, the copy is incomplete. What am I missing?

output: /* 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

Amount of data to copy: 50

1 2 3 4 5 6 7 8 9 10 11 12 13 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 */

Claudiu · Accepted Answer · 2014-02-07 22:12:30Z

4

The third argument to memcpy is the number of bytes to copy. You provided the number of ints. Do this instead:

memcpy ( k_src,
&handle->_context._buf[0],
 handle->_context._bufLen * sizeof(int)
);

edited Feb 7, 2014 at 22:12

answered Feb 7, 2014 at 22:06

Claudiu

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Comments

paxdiablo · Accepted Answer · 2014-02-07 22:07:01Z

4

You're missing the fact that memcpy copies a number of bytes rather than integers. You need to multiply your array size by sizeof(int) when using it with memcpy.

On a little-endian machine with four-byte int type, copying 50 bytes would give you what you see (50 / 4 = 12.5) though the last element 13 would depend on what was already in the destination memory.

answered Feb 7, 2014 at 22:07

paxdiablo

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