Read float from input stream without trailing "E"

Question

I do the following:

float f;
cin >> f;

On the string:

0.123W

Number 0.123 will be properly read to f, and stream reading will be stopped on 'W'. But if we enter:

0.123E

operation will fail and cin.fail() will return true. Probably the trailing 'E' will be treated as part of scientific notation.

I've tried cin.unsetf(std::ios::scientific); with no success.

Is there any possibility to disable treating character 'E' specially?

Answer 1

Yes, you have to parse it your self. Here is some code:

// Note: Requires C++11
#include <string>
#include <algorithm>
#include <stdexcept>
#include <cctype>
using namespace std;

float string_to_float (const string& str)
{
    size_t pos;
    float value = stof (str, &pos);
    // Check if whole string is used. Only allow extra chars if isblank()
    if (pos != str.length()) {
        if (not all_of (str.cbegin()+pos, str.cend(), isblank))
            throw invalid_argument ("string_to_float: extra characters");
    }
    return value;
}

Usage:

#include <iostream>
string str;
if (cin >> str) {
    float val = string_to_float (str);
    cout << "Got " << val << "\n";
} else cerr << "cin error!\n"; // or eof?

Answer 2

You'll need to read the value as a string, and parse it yourself.