Invalid read of size 1 at address

Question

So, I am writing a simple shell program and in my function main, I called “strcmp” to check if the command entered is “env” and “exit”. My code compiles fine but when I run valgrind to check error and memory leak, it brought up segmentation fault as well as “invalid read of size 1 at address”

I expected that when I run “valgrind”, I would get all memory freed

This is the error message:

Invalid read of size 1
==1877==    at 0x483FED4: strcmp (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==1877==    by 0x109806: main (in /root/simple_shell/hsh)
==1877==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==1877== 
==1877== 
==1877== Process terminating with default action of signal 11 (SIGSEGV): dumping core
==1877==  Access not within mapped region at address 0x0
==1877==    at 0x483FED4: strcmp (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==1877==    by 0x109806: main (in /root/simple_shell/hsh)

This is my function main:

                if (tokens == NULL)
                {
                        /* free env before exiting shell */
                        free_env(env_cp);
                        return (-1);
                }
                /* check if the entered command is exit */
                if (strcmp(tokens[0], "exit") == 0)
                {
                        free_env(env_cp);
                        /* Free the allocated memory for tokens */
                        for (i = 0; tokens[i] != NULL; i++)
                        {
                                free(tokens[i]);
                        }
                        free(tokens);
                        exit(EXIT_SUCCESS);
                }
                /* check if the entered command is env */
                if (strcmp(tokens[0], "env") == 0)
                {
                        print_env(env_cp);
                        /* Free the allocated memory for tokens */
                        for (i = 0; tokens[i] != NULL; i++)
                        {
                                free(tokens[i]);
                        }
                        free(tokens);
                        continue;
                }

                execmd(tokens);

                /* Free the allocated memory for tokens */
                for (i = 0; tokens[i] != NULL; i++)
                {
                        free(tokens[i]);
                }
                free(tokens);

        }
        free_env(env_cp);
        return (0);
}