arrays - Memory error - Simple XOR encryption in C -

i having memory issues printing hex in following format: \xaa\xab\xdc using encryption routine.

i did modifications, using snprintf() , strcat() in attempt fix output , worked degree.

this function started out with, better modified version.

char *encrypt(char key, const char *a) {     char *output = malloc(strlen(a)+1);     bzero(output, strlen(a)+1);     strcpy(output, a);     char *tmp = output;     int i;     (i = 0; tmp[i] != 0; i++) {         tmp[i] = key ^ tmp[i];     }     return output; } 

my current progress follows:

char *encrypt(char key, const char *a)  {     char buf[256];     char *tmp = a;     int i;     int *k;      (i = 0; tmp[i] != 0; i++)     {         char temp[10];         k = key ^ tmp[i];         snprintf(temp, sizeof(temp), "\\x%s", k);         strcat(buf, temp);     }     return buf; }  int main(int argc, char **argv) {     if (argv[1] == null){         printf("usage: %s <string>\n", argv[0]);     }     else printf("encrypted string: %s\n", encrypt(0xeb, argv[1]));     return 0; } 

if point me in right direction on how fix memory issue, , if code can improved appreciate lot.

instead of:

int *k; k = key ^ tmp[i]; snprintf(temp, sizeof(temp), "\\x%s", k); 

use this:

unsigned char k; k = key ^ tmp[i]; snprintf(temp, sizeof temp, "\\x%02x", k); 

note have other changes make regarding buf. firstly never initialize it, appending junk. , never check didn't overflow it.

also attempt return function, however, since local variable, ceases exist when function returns.

see this thread suggestions of how freshly-written string out of function. use malloc(256) in same vein first attempt (and remember replace sizeof buf mallocated length, in snprintf call).

---

it'd more robust use unsigned char instead of char both key , message. example of issues on x86 or x64, char has range of -128 127 when supply 0xeb (i.e. 235) out-of-range assignment not well-defined.

but on common systems away using char because tend define out-of-range assignment using 2's complement , truncating excess bits, works in situation.