How Can I Efficiently Check if a C String Represents a Number?

How to Determine if a String Represents a Number in C

Deciphering whether a string constitutes a number is often encountered in programming, particularly in scenarios involving file parsing or data validation. This question explores approaches to identify numeric strings in C .

The original function, isParam, attempted to utilize atoi and isdigit to determine if a string is numeric. While atoi attempts to convert a string to an integer, it is unreliable in detecting non-numeric characters within the string.

Efficient Iteration Approach

A more efficient method involves traversing the string character by character until a non-numeric character is encountered. If the iteration concludes without finding a non-numeric character, the string is considered numeric. Here's the updated function:

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();
}

C 11 Lambda Approach

In C 11 and later, lambdas can simplify this process:

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();
}

Note: These solutions only handle positive integers. For negative integers and fractions, consider using a more comprehensive library-based approach.

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