segmentation faults with string.h into queue - c++

Question

Sorry noob question couldn't figure out which functions to use here.
http://www.cplusplus.com/reference/string/string/
Was gonna convert to c-string and write a whole mess of code but I bet there's a good way to do this.
Just trying to append A, B, and C to the end of a string and add it to queue, keep getting segmentation fault tho that terminates in a ??() function after string::assign() (according to debugger)
string a, b, c;
a = s.append("A");
b = s.append("B");
c = s.append("C");
q.add(a);
q.add(b);
q.add(c);
this too ends with segmentation fault.
q.add(s + "A");
q.add(s + "B");
q.add(s + "C");
Also problem with this is it uses the old, so I'll get:
teststringA
teststringAB
teststringABC
instead of expected
teststringA
teststringB
teststringC

Answer 1

What is a segmentation fault?
When your program runs, it has access to certain portions of memory. First, you have local variables in each of your functions; these are stored in the stack. Second, you may have some memory, allocated during runtime (using either malloc, in C, or new, in C++), stored on the heap (you may also hear it called the "free store"). Your program is only allowed to touch memory that belongs to it -- the memory previously mentioned. Any access outside that area will cause a segmentation fault. Segmentation faults are commonly referred to as segfaults.
your second problem is
q.add(s + "A"); // appends A to s hence teststringA
q.add(s + "B"); // teststringA + B hence teststringAB
q.add(s + "C"); //teststringAB + C hence teststringABC
refer document at http://www.cplusplus.com/reference/string/string/append/
Append to string
The current string content is extended by adding an additional appending string at its end.
The arguments passed to the function determine this appending string:
string& append ( const string& str );
Appends a copy of str.
example
// appending to string
#include <iostream>
#include <string>
using namespace std;
int main ()
{
string str;
string str2="Writing ";
string str3="print 10 and then 5 more";
// used in the same order as described above:
str.append(str2); // "Writing "
str.append(str3,6,3); // "10 "
str.append("dots are cool",5); // "dots "
str.append("here: "); // "here: "
str.append(10,'.'); // ".........."
str.append(str3.begin()+8,str3.end()); // " and then 5 more"
str.append<int>(5,0x2E); // "....."
cout << str << endl;
return 0;
}
Output:
Writing 10 dots here: .......... and then 5 more.....