c++ - Cannot properly memcpy a char array to struct -

so have construct called packet

struct packet {     unsigned int packet_type;     wchar_t packet_length[128];     wchar_t file_name[256];     wchar_t template_name[256];     wchar_t file_name_list[1024];     wchar_t file_data[1024];      void serialize(char * dat) {         memcpy(dat, this, sizeof(packet));     }      void deserialize(const char * dat) {         memcpy(this, dat, sizeof(packet));     } }; 

i'm trying desieralize data

{byte[2692]} [0]    0       unsigned int packet_type; (4 bytes) [1]    0 [2]    0 [3]    0 [4]    50 '2'  wchar_t packet_length[128]; (128 bytes) [3]    0 [5]    54 '6' [3]    0 [6]    57 '9' [3]    0 [7]    50 '2' [8]    0 [...]  0 [132]  112 'p'  wchar_t file_name[256]; (256 bytes) [133]  0 [134]  104 'h' [...]  0 

but memcpy in deserialze isn't giving me file_name, give me packet_length. what's this? thanks!

edit: it's clear me wchar_t taking more space once thought; however, i'm being told not use memcpy @ all?

i've written deserialize method , grabs data correctly. still cause security leak?

void deserialize(const char * dat) {         memcpy(&(packet_type), dat, 4);         memcpy(&(packet_length[0]), dat + 4, 128);         memcpy(&(file_name[0]), dat + 132, 256);         memcpy(&(template_name[0]), dat + 388, 256);         memcpy(&(file_name_list[0]), dat + 644, 1024);         memcpy(&(file_data[0]), dat + 1668, 1024);     } 

the layout of char array assumes size of wchar_t 2 bytes; not - here example of system size of wchar_t 4, size of packet 10756, not 2692 bytes: (link demo).

that why memcpy trick edit presents problem: assumes layout of data in char[] array matches layout of wchar_t[] arrays, may or may not match. if know data array has two-character elements stored in little endian format (lsb first), can write own function converts data source destination, , call portions of serialized data, this:

void bytes_to_wchar(wchar_t *dest, const unsigned char* src, size_t length) {     (size_t = 0 ; != lengt ; i++) {         dest[i] = src[2*i] | (src[2*i+1] << 8);     } } 

now can use function copy data wchar_t arrays independently of wchar_t size on target system, or endianness of target system:

void deserialize(const char * dat) {     bytes_to_wchar(packet_type,       dat + 0,      4);     bytes_to_wchar(packet_length[0],  dat + 4,    128);     bytes_to_wchar(file_name[0],      dat + 132,  256);     bytes_to_wchar(template_name[0],  dat + 388,  256);     bytes_to_wchar(file_name_list[0], dat + 644,  1024);     bytes_to_wchar(file_data[0],      dat + 1668, 1024); } 

the shortcut of saving data memory , writing may work when on same hardware, using same compiler. remains sensitive small adjustments in headers use , in settings of compiler.

if character array need copy struct has fixed layout, need write function process layout, converting two-byte groups wchar_ts, four-byte groups unsigned ints, , on.