c++ - Overwriting custom string failing when non-default ctor was explicitly called -

for exercise in accelerated c++ i'm implementing custom string class called str. worked fine when underlying storage container custom vector (vec) i've run weird situational problem don't understand.

if create new str object explicitly calling constructor str newstr("some words"); , try overwrite using cin >> newstr; program crashes in end, giving sigabrt in debugger when reaches str destructor (which delete[] data;).

this doesn't happen if create new, empty str use cin fill str newstr; cin >> newstr;, or if use cin overwrite str made using str newstr = "some words";, fails when attempt overwrite str made explicitly calling non-default constructor though type displays correctly before being overwritten.

another weird thing in case works fine if don't create new strs between creating/displaying odd-behavior str , using cin change value.

str = "here a"; str b("and here b");  cout << << endl << b << endl;  str c = "finally have c"; cout << c << endl; cin >> c; cout << c << endl << endl;  cin >> b; cout << b << endl; 

this shows you can overwrite str c successfully, crashes when try overwrite str b. this, however, lets overwrite b , program completes successfully:

str = "here a"; str b("and here b");  cout << << endl << b << endl;  cin >> b; cout << b << endl; 

str contains private members char* data, int length, limit , constructor being used both a , b is:

str::str(const char* cp) {     limit = length = std::strlen(cp);     data = new char[length];     (size_type = 0; != length; ++i)         data[i] = cp[i]; } 

i have >> friended , implementation is:

istream& operator>>(istream& is, str& s) {     delete[] s.data;     s.length = s.limit = 0;      char c;     while (is.get(c) && isspace(c)) ;      if (is) {         s.push_back(c);         while (is.get(c) && !isspace(c));          if (is)             is.unget();     }     return is; } 

i know push_back might odd function have in class works fine when using cin long str takes many push_backs. i've tried tweaking different parts of class/operators hours , stumped o_o

lastly, i'm not sure why copy ctor isn't being called (checked couts) during str initialization uses str newstr = "blah"; syntax, though works.

edit, push_back:

void str::push_back(char c) {     if (length == limit) {         limit = std::max(limit*2, 1);         char* newdata = new char[limit];          (size_type = 0; < length; ++i)             newdata[i] = data[i];          delete[] data;         data = newdata;     }     data[length++] = c; } 

when delete[]ing memory in input operator, need make sure data member set 0. if don't that, you'll delete[] non-null pointer delete[]d in push_back() , program have undefined behavior:

istream& operator>>(istream& is, str& s) {     delete[] s.data;     s.data = 0; // needed keep class invariants correct     s.length = s.limit = 0;     // ... }