How to return this array as string?

Question

    static char* test_encrypt_ecb_verbose(char* plain_text_char, char* key_char)
{
uint8_t i,j, buf[64];
uint8_t plain_text[64];
uint8_t* outstr;
outstr = '\0';
memcpy(key,key_char,16) ;
memcpy(plain_text, plain_text_char, 64);
memset(buf, 0, 64);

printf("ECB encrypt verbose:\n\n");
printf("plain text:\n");
for(i = (uint8_t) 0; i < (uint8_t) 4; ++i)
{
    phex(plain_text + i * (uint8_t) 16);
}
printf("\n");

printf("key:\n");
phex(key);
printf("\n");

// print the resulting cipher as 4 x 16 byte strings
printf("ciphertext:\n");
for(i = 0; i < 4; ++i)
{
    AES128_ECB_encrypt(plain_text + (i*16), key, buf+(i*16));
    phex(buf + (i*16));
//function to encrypt
}
printf("decryptedtext:\n");
for (i = 0; i < 4; ++i)
{
    AES128_ECB_decrypt(buf + (i * 16), key, plain_text + (i * 16));
    phex(plain_text + (i * 16));
//function to decrypt
}
//memcpy(outstr, buf, 64);

for (i = 0; i < 4; i++)
{
    for (j = 0; j < 16; j++)
    {
        outstr[j] = buf + (i * 16);
    }
}

In the above code snippet I want to return the output array after encryption as string . Two of my attempts are there at the end. But those aren't correct. Can anyone suggest the correct way?

Answer 1

a char array and a char pointer is not the same thing.

If you need more details you should refer to this post

and it will gives you a solution to get a char * from a char array

char* p = &a[0];

a is your char array and p your destination pointer then return your pointer. Using your code you can also directly use the char * you get as function parameters

Answer 2

To get it back you should add an additional argument:

static void test_encrypt_ecb_verbose(char* plain_text_char, char* key_char, char** cipher_text_char)
{
    ... your function ...

    *cipher_text_char = malloc(64);
    memcpy(*cipher_text_char, buf, 64);
}

From the caller you just do

char* cipher_text_char = NULL;

test_encrypt_ecb_verbose(plain_text_char, key_char, &cipher_text_char);

After test_encrypt_ecb_verbose has been executed, cipher_text_char will point to the memory allocated inside the function.

As an example consider this:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char* myfunc(char* src, char** dst, int len)
{
    *dst = (char*)malloc(len);

    memcpy(*dst, src, len);

    return *dst;
}

int main(int argc, char* argv[])
{
    char* src = "MyFuncTest";
    char* dst = NULL;
    char* p = NULL;

    p = myfunc(src, &dst, strlen(src) + 1);

    printf("dst = %s\n", dst);
    printf("p = %s\n", p);

    return 0;
}

The output is:
dst = MyFuncTest
p = MyFuncTest