How do I remove leading and trailing spaces, and reduce multiple spaces to single spaces in a C string?

Removing Leading and Trailing Spaces from a String in C

This task, commonly known as string trimming, can be accomplished using C 's string class. To address potential extra spaces between words, a separate operation called string reduction is employed.

Trimming Leading and Trailing Spaces

To remove leading and trailing spaces, the trim() function can be defined using the find_first_not_of and find_last_not_of methods:

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);
}

String Reduction

To remove extra spaces between words, the reduce() function performs the following operations:

1. Trims the string using the trim() function.
2. Replaces consecutive spaces with a single space using find_first_of, find_first_not_of, and replace.

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;
}

Usage

The following code demonstrates the usage of the trim() and reduce() functions:

int main(void)
{
    const std::string foo = "    too much\t   \tspace\t\t\t  ";
    const std::string bar = "one\ntwo";

    std::cout << "[" << trim(foo) << "]" << std::endl;
    std::cout << "[" << reduce(foo) << "]" << std::endl;
    std::cout << "[" << reduce(foo, "-") << "]" << std::endl;

    std::cout << "[" << trim(bar) << "]" << std::endl;
}

Output

[too much               space]
[too much space]
[too-much-space]
[one
two]

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