c++ - c_str() custom implementation / "=" in the end of every string -

i'm trying implement c_str() function of custom string class. seems work, reason prints "=" in end of every string:

const char* c_str()     {                char* temp = alloc.allocate(data.size() + 1);         uninitialized_copy(data.begin(), data.end(), temp);         temp[data.size()+1] = '\0';         return temp;     } 

private part of str class:

private:     vec<char> data;     allocator<char> alloc; 

*vec vector.

int main() {     str s1 = "hello, beee";     cout << s1.c_str();     return 0; } 

where wrong?

the problem here:

temp[data.size() + 1] = '\0'; 

the char array allocated data.size() + 1 bytes, indices should 0 data.size(). temp[data.size() + 1] out of array boundary. code may lead undefined behaviors.

it should be

temp[data.size()] = '\0';