How Can I Efficiently Identify Numeric Values Within a String in C ?

How to Identify Numerals Within a String Using C

Coding a function capable of validating whether a string represents a numeric value in C can pose a significant challenge. This article addresses this issue and presents an efficient solution.

Original Attempt

Initially, a function named isParam was developed with the intention of ascertaining whether a line within a text file constituted a numeric value. The function utilized the isdigit and atoi functions, although it encountered unforeseen errors.

Alternative Approaches

Instead of the original function, a different method is recommended. This approach involves traversing the string until a non-numeric character is discovered. If any such characters are identified, the string is deemed non-numeric. Here's the code:

bool is_number(const std::string& s)
{
    std::string::const_iterator it = s.begin();
    while (it != s.end() && std::isdigit(*it)) ++it;
    return !s.empty() && it == s.end();
}

Alternatively, C 11 syntax can be leveraged to achieve the same result:

bool is_number(const std::string& s)
{
    return !s.empty() && std::find_if(s.begin(), 
        s.end(), [](unsigned char c) { return !std::isdigit(c); }) == s.end();
}

Limitations and Enhancements

It's worth noting that the provided solutions only validate positive integers. For scenarios involving negative integers or decimal values, a more comprehensive library-based method would be advisable. Extending the code to handle negative integers is relatively straightforward, but implementing decimal validation requires a more robust approach.

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