How to Trim Leading and Trailing Spaces from a String in C ?

Removing Leading and Trailing Spaces from a String

Trimming leading and trailing spaces from a string object in C is a common task. The string class lacks native methods to accomplish this, but it can be achieved through a combination of string manipulation techniques.

To remove leading and trailing spaces, the find_first_not_of and find_last_not_of functions can be used to identify the first and last non-whitespace characters in the string. Once these positions are determined, the substr function can be employed to extract the substring without the leading and trailing spaces.

#include <string>

std::string trim(const std::string& str) {
    const auto strBegin = str.find_first_not_of(" ");
    if (strBegin == std::string::npos) {
        return "";
    }
    const auto strEnd = str.find_last_not_of(" ");
    const auto strRange = strEnd - strBegin + 1;
    return str.substr(strBegin, strRange);
}

Extending the Formatting to Reduce Extra Spaces

To remove extra spaces between words in a string, a more comprehensive approach is required. This can be achieved by repeatedly using the find_first_of, find_last_not_of, and substr functions to replace subranges of spaces with a placeholder character or string.

std::string reduce(const std::string& str, const std::string& fill = " ") {
    auto result = trim(str);
    auto beginSpace = result.find_first_of(" ");
    while (beginSpace != std::string::npos) {
        const auto endSpace = result.find_first_not_of(" ", beginSpace);
        const auto range = endSpace - beginSpace;
        result.replace(beginSpace, range, fill);
        const auto newStart = beginSpace + fill.length();
        beginSpace = result.find_first_of(" ", newStart);
    }
    return result;
}

Usage Example

The following code snippet demonstrates how to use these functions:

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;

This code will produce the following output:

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

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