使用Char C＃分割字串

Question

How can I efficiently split a string with a character?

An example would be:

inputString = "ABCDEFGHIJ", sectionLength = 4, splitChar = '-', and output = "ABCD-EFGH-IJ"

Here is my first attempt: I wanted to split an input string with certain chars after every nth interval. I am wondering if there is a more efficient way to do this, or if I am missing something that could fail. I believe the If statement at the beginning should catch any invalid input, save null input.

public String SplitString(string inputString, int sectionLength, 
    char splitChar)
{
    if (inputString.Length <= sectionLength || sectionLength < 1)
        return inputString;

    string returnString = "";
    int subStart;
    int end = inputString.Length;

    for (subStart = 0 ; (subStart + sectionLength) < end; 
        subStart += sectionLength)
    {
        returnString = returnString +
            inputString.Substring(subStart,
            sectionLength) + splitChar;
    }

    return returnString + inputString.Substring(subStart, 
        end - subStart);
}

Answer 1

Strings in .NET are immutable . That means operations that combine strings end up creating a brand-new string.

This section of code

for (subStart = 0 ; (subStart + sectionLength) < end; subStart += sectionLength)
    {
        returnString = returnString + inputString.Substring(subStart, sectionLength) + splitChar;
    }

keeps creating new strings.

Instead, explore the use of StringBuilder.

int estimatedFinalStringLength = 100; // <-- Your estimate here
StringBuilder returnString = new StringBuilder(estimatedFinalStringLength);
for (subStart = 0 ; (subStart + sectionLength) < end; subStart += sectionLength)
{
    returnString.Append(inputString.Substring(subStart, sectionLength) + splitChar);
}

return returnString.ToString() + inputString.Substring(subStart, end - subStart);

Doing your best to estimate the total length of the final string will reduce the number of buffer reallocations that StringBuilder does internally.