Question

 struct TokenizerT_ {
    char* separators;
    char* tks;
    char* cur_pos;
    char* next;
  };

  typedef struct TokenizerT_ TokenizerT;

  TokenizerT *TKCreate(char *separators, char *ts) 
  { 
    TokenizerT *tokenizer;
    tokenizer = (TokenizerT*)malloc(sizeof(TokenizerT));

    //some manipulation here

    tokenizer->tks = (char*) malloc (strlen(str)* sizeof(char));
    tokenizer->tks=str;
    printf("size of tokenizer->tks is %zu\n", strlen(tokenizer->tks)); //this prints out the correct number (e.g. 7)
    return tokenizer;
  }

  int main(int argc, char **argv)
  {
    TokenizerT *tk = TKCreate(argv[1], argv[2]);
    printf("tk->tks: %zu\n", strlen(tk->tks)); //HOWEVER, this prints out the wrong number (e.g. 1)
  }

As seen from the above code, I’m working with pointers to structs. For some reason I am not receiving back the correct length for tk->tks. I cannot understand this because it should be the same size as tks in my TKCreate function. Can someone explain this please?

Answer 1

I suspect str, the definition of which is not shown in your code snippet, is a local variable defined in TKCreate(). If so, you’re assigning tokenizer->tks to have the value of str, which points to a proper string inside the scope of TKCreate() but upon exiting TKCreate(), the stack contents (including parameters and local variables) are freed and wiped out so when you try to reference that pointer outside the scope of TKCreate() all bets are off.

One plausible fix is to allocate the storage for tokenizer->tks dynamically, so it persists after you exit TKCreate(). I see you do that with a call to malloc but then you overwrite that with an explicit assignment from str. Instead you should copy the contents of str (using strcpy) into the dynamically allocated memory via: strcpy(tokenizer->tks, str);