Parsing a string into double and string in C++

Question

I have a string like this

string myStr("123ab")

I'd like to parse it into

double d;
string str;

with d=123 and str=ab

I tried using string stream like this

istringstream ss(myStr);
ss >> d >> str;

But it didn't work. What's wrong?

Answer 1

The code in the OP worked as expected for me:

#include <iostream>
#include <sstream>
#include <string>

int main(int argc, char** argv) {
    for (int i = 1; i < argc; ++i) {
        std::istringstream ss(argv[i]);
        double d;
        std::string s;
        if (ss >> d >> s)
            std::cout << "In '" << argv[i]
                      << "', double is " << d
                      << " and string is '" << s << "'\n";
        else
            std::cout << "In '" << argv[i]
                      << "', conversion failed.\n";
    }
    return 0;
}

---

$ ./a.out 123ab
In '123ab', double is 123 and string is 'ab'

(Live on coliru.)

---

However, it fails on input 123eb because the e is interpreted as an exponent indicator and there is no following exponent. There is no simple way around this issue with std::istringstream, which works somewhat like sscanf; fallback is not possible. However, std::strtod should find the longest valid floating point number, and therefore will be able to deal with 123eb. For example:

#include <iostream>
#include <sstream>
#include <string>
#include <cstring>

int main(int argc, char** argv) {
    for (int i = 1; i < argc; ++i) {
        char* nptr;
        double d = strtod(argv[i], &nptr);
        if (nptr != argv[i]) {
            std::string s;
            if (std::istringstream(nptr) >> s) {
                std::cout << "In '" << argv[i]
                          << "', double is " << d
                          << " and string is '" << s << "'\n";
                continue;
            }
        }
        std::cout << "In '" << argv[i]
                  << "', conversion failed.\n";
    }
    return 0;
}

(Live on coliru.)