Error: Abort trap 6 - String obfuscation

Question

I am trying to write code for String Obfuscation but it gives me Abort trap: 6 error while running. Any ideas are much appreciated:

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

char* readLine_str_test_encrypt();
char* readLine_str_test_decrypt();

int main () { //body 

printf("%s\n", readLine_str_test_encrypt());

printf("%s\n", readLine_str_test_decrypt());


}

char* readLine_str_test_decrypt() {
static unsigned char string[9] = {100, 115, 119, 114, 90, 127, 120, 115, 22};

static int i = 0;

for (; i < 9; ++i) {
    string[i] ^= 22;
}

return (char*)string;
}

char* readLine_str_test_encrypt()
{
static unsigned char string[9] = "readLine";
char output[9];
char* output_start=output;
static int i =0;
for(; i < 9; ++i)
{
    //string[i] = string[i]^22;
    output_start += sprintf(output_start,"%d",string[i]^22);

}

return output_start;
}

My decrypt function is running successfully.

Answer 1

In the readLine_str_test_encrypt you are returning a pointer to variable output. This variable is a local variable and goes out of scope when the function exits.

Change it to

static char output[9];  

and the error goes away.

Read more as to why you should not return a local variable here.