How Can C Streams Be Used to Reliably Handle Invalid Numeric Input?

Resolving Invalid Input with C Streams

Problem:

The provided code aims to prevent non-numeric characters from being accepted as input. However, it fails to handle situations where the input includes a character after a valid number.

Proposed Solution:

To address this issue, we suggest employing a different approach using std::getline and std::string.

Code Snippet:

#include <string>
#include <sstream>

int main() {
    std::string line;
    double d;
    while (std::getline(std::cin, line)) {
        std::stringstream ss(line);
        if (ss >> d) {
            if (ss.eof()) {   // Success
                break;
            }
        }
        std::cout << "Error!" << std::endl;
    }
    std::cout << "Finally: " << d << std::endl;
}

Explanation:

This revised solution follows these steps:

1. Read the entire line: Using std::getline, the entire line of input, including spaces and special characters, is taken into a string variable line.
2. Convert the string to double: A std::stringstream object ss is created to hold the string line. The stream is then used to extract the numeric value using the >> operator.
3. Check for successful conversion: If the ss stream successfully extracts the number and reaches the end of the string, it indicates a valid numeric input.
4. Handle errors: If the conversion fails, an error message is displayed.

This approach ensures that only valid real numbers are accepted as input, regardless of any trailing characters or spaces in the input.

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