How do I dynamically allocate multiple strings from the command line argv?-CodePudding

For this assignment I'm supposed to grab multiple names from the command line arguments which are prefaced with either ' ' (which inserts the name into my linked list) or '-' (which removes the name from the list), so if I were to enter " bill jim ted -bill", I would add those three names without the ' ' and remove bill. Ive tried to dynamically allocate a string using malloc so I can modify the name string, but my code doesnt insert the string data into my linked list, and I get a free(): invalid pointer error when I pass through some test strings. If I move the free(name) statement to the if/else if statements I get a segmentation fault. How would I go about dynamically allocating these strings from the command line correctly so they can be modified?

int main(int argc, char *argv[]){
    struct node* head;
    for(int x = 0; x < argc; x  ){
            char * name = malloc((strlen(argv[x]) 1));
            name = argv[x];
            if(name[0] == ' '){
                    printf("adding %s \n", name  );
                    insert(&head, name  );
                    printf("List: ");
                    printList(&head);
            }
            else if(name[0] == '-'){
                    printf("removing %s \n", name  );
                    removeNode(&head, name  );
            }
            free(name);
    }

}

CodePudding user response：

Try using strcpy(name, argv[x]); instead of name = argv[x], because when you assign a pointer to a pointer, they will lead to the same memory location where your null-terminated char array is stored. So that you could've done a memory deallocation for the argv[x] when you called free(name);

The pointer opperations are not the same as value assignments.

also see this thread: How do malloc() and free() work?

CodePudding user response：

Many problems

Incorrect copying of string

    //char * name = malloc((strlen(argv[x]) 1));
    //name = argv[x];
    char * name = malloc(strlen(argv[x]) 1);
    if (name == NULL) return EXIT_FAILURE; // Out of memory
    strcpy(name, argv[x]);

Incorrect free()

Code needs to free the same value received from allocation. name messes that up.

Uninitialized head*

// struct node* head;
struct node* head == NULL;

More

Likely only need to allocate when adding and allocated after the /-.

int main(int argc, char *argv[]){
  struct node* head = NULL;
  // for(int x = 0; x < argc; x  ){
  for(int x = 1; x < argc; x  ){  // Skip adding the program name, start at 1
    if(argv[x][0] == ' '){
      char * name = malloc((strlen(argv[x]   1) 1));
      if (name == NULL) return EXIT_FAILURE; // Out of memory
      strcpy(name, argv[x]);
      printf("adding %s \n", name);  // No   
      insert(&head, name); // No   
      printf("List: ");
      printList(&head);
    }
    else if(argv[x][0] == '-'){
      printf("removing %s \n", argv[x]   1);
      // This is a problem, I'd expect removeNode() to return a pointer to the free'd name
      char *name = removeNode(&head, argv[x]   1);
      free(name);
    }
  }