How to Efficiently Remove Leading, Trailing, and Extra Spaces from a C String?

Removing Leading and Trailing Spaces from a String in C

Problem:

How do we efficiently remove leading and trailing spaces from a C string? Additionally, how can we extend this operation to remove extra spaces between words in the string?

Solution:

Removing Leading and Trailing Spaces:

• find_first_not_of(char): Use this function to find the first character in the string that is not a whitespace character.
• find_last_not_of(char): Use this function to find the last character in the string that is not a whitespace character.
• substr(start, length): Use this function to extract the substring between the start index and the specified length.

std::string trim(const std::string& str, const std::string& whitespace = " \t") {
    const auto strBegin = str.find_first_not_of(whitespace);
    if (strBegin == std::string::npos)
        return ""; // No content

    const auto strEnd = str.find_last_not_of(whitespace);
    const auto strRange = strEnd - strBegin + 1;

    return str.substr(strBegin, strRange);
}

Reducing Extra Spaces:

• find_first_of(char): Use this function to find the first whitespace character in the string.
• find_first_not_of(char): Use this function to find the first non-whitespace character after the whitespace character.
• replace(start, length, new_str): Use this function to replace the specified range of characters with a new string.

std::string reduce(const std::string& str, const std::string& fill = " ", const std::string& whitespace = " \t") {
    // Trim first
    auto result = trim(str, whitespace);

    // Replace sub ranges
    auto beginSpace = result.find_first_of(whitespace);
    while (beginSpace != std::string::npos) {
        const auto endSpace = result.find_first_not_of(whitespace, beginSpace);
        const auto range = endSpace - beginSpace;

        result.replace(beginSpace, range, fill);

        const auto newStart = beginSpace + fill.length();
        beginSpace = result.find_first_of(whitespace, newStart);
    }

    return result;
}

Example:

const std::string foo = "    too much\t   \tspace\t\t\t  ";
const std::string trimmedFoo = trim(foo);
const std::string reducedFoo = reduce(foo);

std::cout << "Original: " << foo << std::endl;
std::cout << "Trimmed: " << trimmedFoo << std::endl;
std::cout << "Reduced: " << reducedFoo << std::endl;

Output:

Original:     too much        space              
Trimmed: too much space
Reduced: too-much-space

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