Question

Can I persuade operator>> in C++ to read both a hex value AND and a decimal value? The following program demonstrates how reading hex goes wrong. I’d like the same istringstream to be able to read both hex and decimal.

#include <iostream> #include <sstream>  int main(int argc, char** argv) {     int result = 0;     // std::istringstream is("5"); // this works     std::istringstream is("0x5"); // this fails      while ( is.good() ) {         if ( is.peek() != EOF )             is >> result;         else             break;     }      if ( is.fail() )         std::cout << "failed to read string" << std::endl;     else         std::cout << "successfully read string" << std::endl;      std::cout << "result: " << result << std::endl; } 

Answer 1

Use std::setbase(0) which enables prefix dependent parsing. It will be able to parse 10 (dec) as 10 decimal, 0x10 (hex) as 16 decimal and 010 (octal) as 8 decimal.

#include <iomanip> is >> std::setbase(0) >> result;