istringstream not changing c++

Question

I have written some code to show a problem I am having within another program to convert some input strings .

#include <iostream>
#include <sstream>
#include <bitset>

using namespace std;

int main()
{
    string        tempStr;
    unsigned long tempVal;
    istringstream tempIss;
    bitset<32>    tempBitset;

    // Input the first word in hex and convert to a bitset

    cout << "enter first word in hex : ";
    cin >> tempStr;
    tempIss.str(tempStr);
    cout << "word2 tempIss : " << tempIss.str() << endl;
    tempIss >> hex >> tempVal;
    cout << "word2 tempVal : " << (int)tempVal << endl;
    tempBitset = tempVal;
    cout << "word1 tempBitset: " << tempBitset.to_string() << endl;

    // Input the second word in hex and convert to a bitset

    cout << "enter second word in hex : ";
    cin >> tempStr;
    tempIss.str(tempStr);
    cout << "word2 tempIss : " << tempIss.str() << endl;
    tempIss >> hex >> tempVal;
    cout << "word2 tempVal : " << (int)tempVal << endl;
    tempBitset = tempVal;
    cout << "word2 tempBitset: " << tempBitset.to_string() << endl;

    return 0;
}

My problem is that whilst the value of tempIss appears to change with the tempIss.str(tempStr); function, the following tempIss >> hex >> tempVal; appears to use the old value of tempIss!?

Thanks.

Answer 1

tempIss.str(tempStr);

This merely sets the content of the intenal buffer. It does not, however, reset the error flags that could be set on the stream from previous operations.

Saying tempIss.clear(); before you extract the second time should do the job.