For a personal project I have been implementing my own libstdc++. Bit by bit, I've been making some nice progress. Usually, I will use examples from http://www.cplusplus.com/reference/ for some basic test cases to make sure that I have the obvious functionality working as expected.
Today I ran into an issue with std::basic_string::replace, specifically with the iterator based versions using the example copied verbatim from the site (http://www.cplusplus.com/reference/string/string/replace/) (I've added a comment to point out the lines in question):
// replacing in a string
#include <iostream>
#include <string>
using namespace std;
int main ()
{
string base="this is a test string.";
string str2="n example";
string str3="sample phrase";
string str4="useful.";
// function versions used in the same order as described above:
// Using positions: 0123456789*123456789*12345
string str=base; // "this is a test string."
str.replace(9,5,str2); // "this is an example string."
str.replace(19,6,str3,7,6); // "this is an example phrase."
str.replace(8,10,"just all",6); // "this is just a phrase."
str.replace(8,6,"a short"); // "this is a short phrase."
str.replace(22,1,3,'!'); // "this is a short phrase!!!"
// Using iterators: 0123456789*123456789*
string::iterator it = str.begin(); // ^
str.replace(it,str.end()-3,str3); // "sample phrase!!!"
// *** this next line and most that follow are illegal right? ***
str.replace(it,it+6,"replace it",7); // "replace phrase!!!"
it+=8; // ^
str.replace(it,it+6,"is cool"); // "replace is cool!!!"
str.replace(it+4,str.end()-4,4,'o'); // "replace is cooool!!!"
it+=3; // ^
str.replace(it,str.end(),str4.begin(),str4.end());
// "replace is useful."
cout << str << endl;
return 0;
}
In my version of replace is implemented in terms of a temporary string which I create then swap with *this. This clearly invalidates any iterators. So am I correct that the example is invalid? because it stores iterators, does a replace and then uses the iterators again?
My copy of the standard (ISO 14882:2003 - 21.3p5) says:
References, pointers, and iterators referring to the elements of a basic_string sequence may be invalidated by the following uses of that basic_string object:
- As an argument to non-member functions swap() (21.3.7.8), operator>>() (21.3.7.9), and getline() (21.3.7.9). - As an argument to basic_string::swap(). - Calling data() and c_str() member functions. - Calling non-const member functions, except operator[](), at(), begin(), rbegin(), end(), and rend(). - Subsequent to any of the above uses except the forms of insert() and erase() which return iterators, the first call to non-const member functions operator[](), at(), begin(), rbegin(), end(), or rend().
The entry about non-const member functions seems to cover this. So unless I am missing something, then this code is using invalidated iterators right? Of course this code works just fine with gcc's libstdc++, but we all know that proves nothing as far as standards compliance.