C - Trying to build a simple shell in linux and having trouble with strtok, realloc in a loop -

trying build shell implementation in linux assignment , having trouble. following error after running 3/4 times loop

* error in `./1': realloc(): invalid next size: 0x000000000132c150 * aborted (core dumped)

i have left parts of code out it's long , know there's no issues them. if there's other parts need can add them too. in advance :)

note: argc , argv global variables

int argc = 0; char **argv = null;   int main(void) {        while(1)     {         catch_signal();         printdate();         readcommand();          if(strcmp(argv[0], "cd") == 0)         {             changedirectory();         }         else         {             executecommand();         }         //free(argv);     }    }  void readcommand() {     char *buffer = null;     char *token = " ";     char *p;      size_t len = 0;     int = 0;      getline(&buffer, &len, stdin);     p = strtok(buffer, "\n");     p = strtok(buffer, token);      while(p)     {         argv = realloc(argv, sizeof(char *) * ++i);          argv[i - 1] = p;         p = strtok(null, token);     }     argc = i;     argv[argc] = null;     free(p); }  void executecommand() {     int status;     pid_t pid;      if((pid = fork()) < 0)     {         printf("error: forking child process failed.");     }     else if(pid == 0)     {        if(execvp(argv[0], argv) < 0)        {            printf("error");            exit(1);        }     }     else     {        while(wait(&status) != pid);     } } 

you reallocating argv array 1 pointer short. there not enough space final null pointer. consider replacing while(p) loop code:

if (!p) {     /* deal empty command line */ }  while (p) {     argv = realloc(argv, sizeof(char *) * (i + 2));     argv[i++] = p;     p = strtok(null, token); } 

p should start null if user entered actual command. if buffer contains empty string or blank one? strtok return null directly in these cases. should ignore such command lines.